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Garage => Mechanicals => Topic started by: Jan S on 10 June 2021, 03:36 PM

Title: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 June 2021, 03:36 PM
I have a 1978 6.9 engine with K-jetronic (and a manually controlled cold-start valve, i.e. I activate the cold start valve by pushing the button for 2-3 sec before I start cold)

- The car starts immediately, cold and warm.
- However, cold start is a bit rough, idle is 1500-1600 rpm
- After 10-15 min engine runs smooth, idle is 900-950
- The ambient temp is 68-77 deg F/ 20-25 deg C.
- In April I checked the fuel pressures (system pressure, control pressure), they were ok (my entire fuel assembly at the rear is new)

Sounds familiar?

Could it be aux air valve, spray pattern injectors, vacuum leaks, ......?

A few tips would be great.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 10 June 2021, 05:24 PM
You might have to define what you mean by "rough running".  Sounds like overly rich?  In my experience they tend to run a bit rich at warm up but 1500-1600 does sound a bit high at those ambient temperatures.
Sounds like you might have to take a look at the warm up regulator action.
With engine fully warmed up your idle should be lower @ 600 - 700 rpm.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: revilla on 10 June 2021, 09:08 PM
Very likely it's your AVV that's a bit stuck and not fully open when cold. Yes, the system is designed to run rich when cold for about 3-5 minutes. But if the AVV is working the engine will run at around 2500 rpm "hiding" the roughness of the engine running rich. There are some accounts that the AVV is reparable. I have simply removed them, cleaned  them and lubricated the visible part of the internal piston. It should slide freely when you submerge the bulb is a bucket with water and ice and immediately put it in a bucket with hot (90C) water. You'll see the piston moving to both extreme positions then you can lubricate the assembly. If your piston doesn't move with the practical test above or its displacement is limited to 2-4 mm then the hypothesis of a misbehaving AVV is confirmed. I have seen that a few times.
Your engine starts as it should cold and hot, so I would not mess with the WUR as it's doing its job just fine. However, you can play with your 3mm allen screw on top of the FD to fine tune the mixture cold/hot. That should help, but if the AVV is stuck that won't change matters significantly.
I hope all that makes sense.
Good luck
Robert
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: s class on 10 June 2021, 10:59 PM
The fact that you have a differential in idle speed from 1500 cold to 900 warm tells me the AAV is most likely OK.  I would regard a differential of 600rpm to be close to ideal. 

I would start with the basics - check and set ignition timing, make sure the vac advance is working.  Then reduce the warm idle speed to 650 and set the warm running fuel mixture properly using a decent exhaust gas analyser.  This will affect both cold and hot running.  It sounds to me like you have it set to rich.

Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Randys01 on 12 June 2021, 02:21 AM
I get the impression this erratic running has come on quickly rather than an observation over many weeks or months?
If indeed it's come on quick I would target air leaks in the inlet tract. Costs nothing..split hose..something's dropped off.??
The engine seems to be running 200 rpm more than it should at both cold n hot. Reduce hot idle to 700 and see next day what effect it has on the cold start idle. if it is still hi at 1500 double check your cold control pressure at the WUR. You said they were fine a few mths ago..is that still the case?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 13 June 2021, 03:47 PM
Thanks to all of you for your assessments and tips - much appreciated.

To daantjie: the rough running is slight engine vibration at 1500-1600 rpm (noticeable more than when warm, warm is smooth). Yes, my assessment is that it's running a bit rich. Regarding the warm-up regulator: In April the engine showed the same running pattern as today. In April I measured the system pressure 5.2 bar (5.2-5.8 bar is the design spec), control pressure cold at around 10 deg C 1,0 bar (spec says 0.7-1.1 bar) and control pressure fairly warm 3.2 bar (spec says 2.8-3.2 bar NO vacum and 3.4-3.8 bar WITH vacum). That tells me the WUR was fairly ok in April. I haven't measured it recently. Yes, I would love to reduce it to 700 rpm, but I need to be making the right adjustments.

To Robert: good tip about the AAV. Is the cleaning and testing of the AAV a fairly straight forward DIY job, or can other issues emerge? I'm planning a longer road trip in 4-weeks time and I will not risk being stranded in my own garage waiting for parts etc. This might be a job for later this fall.

To s-class: yes, I probably has to get some professional help with the ignition, idle speed and warm running fuel mixture.

To Randys01: the rough running and high idle has been there from the start (two years ago when I bought the car). I started at the rear and replaced the entire fuel assembly. That fixed a lot, e.g. easy to start both cold and warm. Now I have to fix the correct idle speed and fuel mix when warm. I haven't measured the fuel pressures since April.

Next step: I believe I will start by checking the ignition, set the correct idle speed and fuel mix when warm. And see what happens with cold start.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: raueda1 on 13 June 2021, 06:03 PM
You're certainly on the right track.  A couple thoughts:

1.  I'm no expert, but my experience has been that everything on these engines is interrelated.  Unless it's all right, nothing is right and it's very easy to go down the wrong path and make yourself nuts.  You already did the rear end of the fuele system.  So keep going:

2. Get this manual if you possibly can:  "1976 1979 Mercedes Continuous Injection System Diagnosis & Adjustment Manual."  I have it as a set of pdf files, can't remember where I got it.  Unfortunately files are too big to download.  It should be in the technical section but is not.  Anyway, it runs through the whole k-jetroninc testing sequence in an ordered way.  It changed my life, it's that good.  PM me with your email and I'll send it to you in bits.

3.  As suggested above, also check timing.  But I'd take it one step further.  Your distributor is very old and almost certainly filthy inside.  This can cause timing to be unstable, so clean it up.  Do a search, there's a detailed thread on the process.  It isn't very hard and afterwards you'll know it's working right.  The difference it made on my car was NOT small!

If I had done the above all at once instead of messing around bit-by-bit it would have saved me a lot of grief.  Stick with it and Good Luck!
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: revilla on 13 June 2021, 09:43 PM
Hi Jan,
To answer your question. Removing/testing/cleaning/lubricating the AAV implies no risk for your trip. It's all quite simple and it doesn't involve buying other parts. There's a small gasket that goes with it that might be deteriorated, if that's the case you can easily make one (we're talking air at not very high pressure (vacuum actually) so no big deal) to ensure no uncontrolled air leaking in.
I insist, leave your WUR alone for now, your engine starts as it should and your fuel pressures (all 3) are where they suppose to be by spec. Timing, if not done already, is your next step after AAV to improve your low idle/cold issue. There's a procedure for that (attached) which involves not only idle check but 1500 and 3000 rpm too. That's important because it will tell you whether other components (i.e. vacuum advance, membranes, distributor springs/weights, etc) are doing it's job. However, warning, I won't open the inside of the distributor before your trip, it can be a pandora box if it's your first time! It's worth doing it but without pressure after your trip. The condition of the cap/rotor you can check, but I wouldn't venture to get to the guts. Your low idle speed when cold issue is not coming from there anyway.
There are two styles of approaching these type of improvements: changing parts left and right and crossing your fingers is one. Some call that changing parts "by principle".  If you feel like "praying" each time you change a part, there's your confirmation you're on style 1.
The second one is to understand the mechanics of a system and its components to be able to diagnose, test, root cause and change the right part(s) with certitude and without crossing the fingers. The advantage of the latter is the gaining in knowledge, the learning experience and the possibility to solve many issues in the future thanks to that know-how base. You'll save hours of time actually. Both schools are valid, you need to understand which is yours.
Please keep us posted on the results.
Cheers.
Robert
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Randys01 on 13 June 2021, 11:46 PM
.".but my experience has been that everything on these engines is interrelated.  Unless it's all right, nothing is right and it's very easy to go down the wrong path and make yourself nuts. "

Never a wiser passage has graced this Board................!! ::)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 15 June 2021, 03:33 PM
Great advice from all of you - thanks a lot!

Conclusion is I will start tackling this issue after my 5000 km road trip, i.e. it will be my fall job. Fingers crossed.

To Robert: I'm trying to be a style 2 guy, I like the learning experience  :) It worked well with the replacement of the fuel assembly - not enough fuel pressure (i.e. the pump was toast) and the system couldn't hold the pressure (i.e. the accumulator was toast). Fairly easy to diagnose after measuring the 3 pressures. Let's see how it goes this time  :-\

I will keep you posted, be patient.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 15 September 2021, 08:53 AM
I'm starting to direct my attention to "the rough and high idle cold start" problem I mentioned before the summer. I will investigate step-by-step according to the manual "1976 1979 Mercedes Continuous Injection System Diagnosis & Adjustment Manual". I'm suspecting a few things at the front .... time will tell (the entire fuel assembly at the rear is new, replaced spring 2021). Will be exciting to follow the guide and learn.

Recently, a new annoying "problem" has surfaced:

- there seems to be fine pulsations/vibrations coming from the combustion, especially when the engine is cold and for the first hour driving the car.
- the pulsations seems to diminish after 1-2 hours (at least it feels that way).
- the pulsations can be felt through the seats when driving
- difficult to estimate the frequency .... I would guess 10-20 per seconds

I might stumble over the problem and the fix when following the k-jet testing manual, but I first wanted to check with you guys if this is a familiar problem.

If I were to guess .... maybe the fuel distributor (FD) is reaching its life ..... or the injection nozzles .... ?

Any tips to direct my assessments are much appreciated.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 15 September 2021, 01:06 PM
Well I would say 1 - 2 hours is a very long time to have warm - up related issues.  Usually your engine should come up to operating temp of 87C fairly quickly with sedate type driving within 5 minutes or so, depending of course on ambient temps.  It may still or course be a WUR or FD (or both) issue however you may need to describe more exactly what type of vibrations you mean.  Are you meaning like a misfire when idling, under load, or both?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 15 September 2021, 02:19 PM
I agree this is not a "normal" warm-up issue. The subjective feel is that the vibrations diminish after 1-2 hours, but maybe not ..... maybe I get used to it?

I did a new 30 min test drive this evening. The pulsations are apparently at their strongest around 50-60 miles/hour with a certain load on the engine (e.g. uphill).

The pulsations are fine, not dominant, and yes - it reminds me of slight misfire .... or constraints/variations in the fuel supply to the combustion chamber.

I didn't noticed this before the summer (again subjective feeling), and since then I haven't worked on engine related things, fuel supply etc. -- only suspension, steering, brakes, etc.

-- could it be the pressure damper sitting between FD and WUR ..... maybe the membrane is shot, which means the fuel pressure to WUR is not that stable, and the leak from the pressure damper leads fuel back to the air inlet, which makes the car run much richer I guess, which means revs should go down I guess?
-- the electronic ignition?

A lot of guessing at the moment :-)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: TNNBENZ on 23 September 2021, 05:58 PM
 "1976 1979 Mercedes Continuous Injection System Diagnosis & Adjustment Manual" is in the technical library !!!  ;)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: raueda1 on 24 September 2021, 08:02 AM
Quote from: TNNBENZ on 23 September 2021, 05:58 PM
"1976 1979 Mercedes Continuous Injection System Diagnosis & Adjustment Manual" is in the technical library !!!  ;)
Yes, this. ^^^     I think this is, by far, the single most useful guide on the site as it applies to an enormous fraction of the issues discussed here.  Start at the beginning and work your way through in sequence.  Chasing specific problems such as this or jumping around will just make you nuts.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 24 September 2021, 01:27 PM
Yes, I have opened the file and started reading  :D

I will go step by step. The story will continue ......
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 03 October 2021, 09:52 AM
Yesterday I visited a local K-/KE-jet specialist, as part of a local MB enthusiast club event.

He did some quick tests of the CO-level on several cars, including mine (US 1977 6.9). No time nor the event for more extensive tests.

The idle screw was at its end point. Still the idle was approx 900 rpm warm. This is too high -- 700-750 rpm is probably more correct. I suspect the cooling water thermostat is shot, and I need to check/clean the aux air valve.

The engine was running way too rich (CO = 4.14 and Lambda = 0.89). He adjusted the CO and we stopped at CO = 2.17 which is probably still a bit too rich. Anyhow, I will leave it there for now and do a new reading after I have replaced the thermostat and checked the aux air valve (and done the other K-jet tests).

Any comments on the BEFORE and AFTER test results?

Before / After:
CO 4.14 / 2.17 %vol
CO2 11.99 / 12.91 %vol
HC 429 / 359 ppmvol
O2 0.62 / 1.43 %vol
Lambda 0.89 / 0.98

Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: UTn_boy on 03 October 2021, 01:07 PM
Did the expert think to ask of your intake upper to lower intake manifold plenums had been resealed or not?  This will also cause a high idle and possible a run rich condition if the system tries to compensate for a lean (too much air) condition. 
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 04 October 2021, 02:45 PM
A crowded event, hence not much time for one-to-one discussions. He mentioned vacuum leaks in general.

I will start with the AAV and the termostat, and take it from there.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 24 October 2021, 11:19 AM
Yesterday I replaced all 8 injectors inclusive the rubber seatings.

They had to go - old and rubber seatings were stone hard.

I tested them with a borrowed tester - both new and old. Spray patterns were fairly ok, but half of them leaked and had a tendency to squirt instead of a "fine shower". New injectors were fine.

Unfortunately the tester had a diesel gauge 0-3000 psi - impossible to check release pressure in the range 3.5-4.5 bar. Good enough for now.

Car started immediately. But rough idle cold is still there. Cleaning cooling system and replacing thermostat this week. Then the newly inspected, tested and cleaned AVV will work as it's supposed to.

Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: TNNBENZ on 26 October 2021, 08:36 AM
   Is the idle lean or rich. Do you smell gas, any smoke or gas smell from exhaust pipe ?  At this very moment I am watching a video on the k-jet system.   Pierre Hedary on youtube.
He is not as good as uncle Kenny but he tries... :P ha
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: ptashek on 26 October 2021, 10:01 AM
Quote from: TNNBENZ on 26 October 2021, 08:36 AM
He is not as good as uncle Kenny but he tries... :P ha

His presentation skills are mediocre, but I'd rather watch Pierre making sense in a weird way, than Kent waffling about to sell more of his stuff.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: TNNBENZ on 26 October 2021, 10:10 AM
Quote from: Jan S on 24 October 2021, 11:19 AM
Yesterday I replaced all 8 injectors inclusive the rubber seatings.

They had to go - old and rubber seatings were stone hard.

I tested them with a borrowed tester - both new and old. Spray patterns were fairly ok, but half of them leaked and had a tendency to squirt instead of a "fine shower". New injectors were fine.

Unfortunately the tester had a diesel gauge 0-3000 psi - impossible to check release pressure in the range 3.5-4.5 bar. Good enough for now.

Car started immediately. But rough idle cold is still there. Cleaning cooling system and replacing thermostat this week. Then the newly inspected, tested and cleaned AVV will work as it's supposed to.
Fuel return line maybe blocked ???
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 28 October 2021, 03:53 PM
I measured the CO before I replaced the injectors. Idle varm 2.18%vol. So I would say a bit rich?

Next on my list:
-- to clean the cooling system and replace the thermostat. That will result in a fully closed aux air valve when warm (the valve has been cleaned and tested. Fully closed at 80 deg C). That job will be done 1-2 weeks from now.

-- adjust idle to 700-750 1/min (warm), if possible

-- a new CO test and adjustment

-- do the tests described in the k-jet manual, including searching for vacuum leaks.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 09 January 2022, 09:34 AM
NEW PROBLEM  >:(

All new/renovated parts have been assembled (radiator, hoses, thermostat, thermostat housing, etc.) and new coolant has been added (50-50 Comma antifreeze and demineralized water)

Engine started immediately (hasn't run since oct/nov 2021). Always a good sign ;D.

I let the car idle for 15 min. It seems the coolant doesn't reach the correct temperature. That means the aux air valve (AAV) doesn't fully close, which means idle is still too high (900 rpm).

The thermostat is new. What can be at play here?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: UTn_boy on 09 January 2022, 09:42 AM
Did you install an aftermarket thermostat or a genuine Mercedes thermostat?  Aftermarket thermostats are often bad out of the box.  Also, have you confirmed the engine temperature with an infrared thermometer to make sure your gauge and/or temperature sending unit isn't reading incorrectly? 
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 09 January 2022, 09:43 AM
Maybe you have some air bubbles stuck in the coolant path  however in my experience this usually leads to rapidly rising temp on gauge. 
Let it cool down then "burp" the coolant tank by opening the cap.  Also you can run the heater when you start it again to make sure the coolant is circulating through the heater core.  Might have to burp it a few times to get all the air out.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 09 January 2022, 12:05 PM
Quote from: UTn_boy on 09 January 2022, 09:42 AM
Did you install an aftermarket thermostat or a genuine Mercedes thermostat?  Aftermarket thermostats are often bad out of the box.  Also, have you confirmed the engine temperature with an infrared thermometer to make sure your gauge and/or temperature sending unit isn't reading incorrectly?

Yes, I bought an aftermarket thermostat (Mahle). I will buy a Mercedes part next week to eliminate that uncertainty.

No, I haven't measured the temperature with a thermometer. I can touch the big radiator hose (from thermostat to radiator inlet), and it doesn't feel warm .... I would guess 60 deg C. This is very subjective.

Where should I measure? Thermostat housing cover, or the big hose?

I will also force-close the AAV by putting a plug in it (after the engine is warm), just to see what happens when the AAV is definitely closed.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 09 January 2022, 12:11 PM
Quote from: daantjie on 09 January 2022, 09:43 AM
Maybe you have some air bubbles stuck in the coolant path  however in my experience this usually leads to rapidly rising temp on gauge. 
Let it cool down then "burp" the coolant tank by opening the cap.  Also you can run the heater when you start it again to make sure the coolant is circulating through the heater core.  Might have to burp it a few times to get all the air out.

Yes, I had bubbles in the system before this job (the heater made gurgling-noises, very irritating). And yes, I forgot to turn on the heater today.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: goldacre on 10 January 2022, 01:10 AM
Hi JanS, was reading how the gubbins under the plenum which is in 2 parts can cause high idle if the rubber connectors are perished, they are out of sight out of mind so can cause vacuum leaks to affect idle but in my situation was isolated to cylinders 7 and 8 have a leak somewhere and idle was very rough, we worked this out by getting gas cylinder and unscrewing the connection to bbq so keeping the hose and regulator on cylinder then turning on the gas and gently poking the hose down into the plenum area, idle smoothed out in and around cylinders 7 and 8 so this caused the suspicion a vacuum leak (Propane is high octane around 110 I think ). Parts arrived from classic centre and included everything rubber for the Inlet system, and TJ450 donated new inlet manifold gadgets a while back, these parts presently on car are 43 years old...  :-\

while your at it check for vacuum at the hose on the right hand side of the engine as you face it, this is connected to the inlet and provides the vacuum for the positive crankcase ventilation, the 2mm venturi was blocked and when cleaned and refitted my idle screw had to be wound down quite a fair way. Will start this repair process soon and if can get pics on Org will do a thread on it  8)

Good luck!

G
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 January 2022, 09:20 AM
Thanks for your tips, goldacre!

The hose you mentions is on my to-do list. But first I need to fix the cooling system and make sure I get the right coolant temperature. Then the Aux Air Valve will fully close.

The rubber connectors under the plenum are indeed out of sight but not out of my mind :) Is also on my to-do list, but later. I haven't been working in those areas before, hence I'm not able to visualize in my head how you tested around cyl. 7 and 8 with gas and that hose. But I believe I understand your aim. I might come back to you on this test, later.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 January 2022, 11:57 AM
Both new and old thermostats work according to spec -- new opens at 87 deg C and old opens at 79 deg C (California car, a previous owner put in a "colder" Thermostat, spec says 87 deg C)

Where do I find the coolant temp sensor? Need to do a bit research  :)

I also want to force-close air through the aux air valve (AAV) to see if rpms remain at 900. No change in rpm I guess the AAV works as it should ......

I suspect the engine has a serious vacuum leak, somewhere. >:(

Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 January 2022, 01:56 PM
Re-installed the new thermostat tonight and idled the engine for about 30 min.

Idle cold 1100 rpms, then increases to 1400 rpms, followed by a descent to approx 900 rpms warm, all in about 15-20 min.

The temperature gauge shows approx 130 deg F (55 deg C) when warm, see pic (I assume the mark between 100 and 175 deg F is 137,5 deg F?)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: revilla on 10 January 2022, 02:27 PM
Hi Jan,
As suggested before, your temperature sensor is most likely at fault. They are available at MB or ebay or auto-doc in Europe, not expensive and easy to replace. By experience, cleaning them doesn't solve the problem. They loose their calibration with time/cycles.  A new one will solve your "low" temp issue. Your old thermostat was probably working just fine, but the sensor was sending a wrong value to the gage. I had this happened to me 2 times in W116s.
If you want to test sensor, you can remove it from engine, then re-connect its cable, then ground it through its body to the chassis, then put a heat source to the bulb, see what the gage does.  Ignition in position 1, do not start the engine, coolant will spill all over your garage, unless you plug the empty slot.   Probably a 2 people task.
Good luck
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 10 January 2022, 02:38 PM
Indeed if we assume your gauge is reading low, then a 900 rpm idle is for sure too high for a fully warmed up engine.  You can also use an IR temp gun to read the temp at the thermostat housing.  Granted it will be lower than the actual water temp but it should give you an idea of what's going on.  87C at the hose is almost too hot to touch, depending on how tough you are of course  ;D
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 January 2022, 04:11 PM
Quote from: revilla on 10 January 2022, 02:27 PM
Hi Jan,
As suggested before, your temperature sensor is most likely at fault. They are available at MB or ebay or auto-doc in Europe, not expensive and easy to replace. By experience, cleaning them doesn't solve the problem. They loose their calibration with time/cycles.  A new one will solve your "low" temp issue. Your old thermostat was probably working just fine, but the sensor was sending a wrong value to the gage. I had this happened to me 2 times in W116s.
If you want to test sensor, you can remove it from engine, then re-connect its cable, then ground it through its body to the chassis, then put a heat source to the bulb, see what the gage does.  Ignition in position 1, do not start the engine, coolant will spill all over your garage, unless you plug the empty slot.   Probably a 2 people task.
Good luck

Thanks, revilla! I will buy a new one. But, can you help me with the location of the sensor? Alternative is to go searching tomorrow  :)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 January 2022, 04:17 PM
Quote from: daantjie on 10 January 2022, 02:38 PM
Indeed if we assume your gauge is reading low, then a 900 rpm idle is for sure too high for a fully warmed up engine.  You can also use an IR temp gun to read the temp at the thermostat housing.  Granted it will be lower than the actual water temp but it should give you an idea of what's going on.  87C at the hose is almost too hot to touch, depending on how tough you are of course  ;D

Thanks, daantjie ..... yes, UTn_boy also suggested IR temp gun. I guess I will buy a new sensor before acquiring a temp gun, to see if that solves the thing.

Can you help me with the location of the sensor?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 10 January 2022, 04:35 PM

[/quote]


Can you help me with the location of the sensor?
[/quote]

OK I assume you mean the sending unit for the gauge?  You will see it kind of hidden at the left far back against the firewall side (as you are standing in front of the car looking at the engine bay).  So it would be at the passenger side (for left hand drive), on the inboard side of the valve cover.  You will see 2x sensors/senders here next to one another.  One is for the cold start injector, and the other one is for the temp gauge.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 11 January 2022, 03:28 AM
Perfect, thanks a lot!
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: goldacre on 11 January 2022, 03:46 AM
Hi Jan S, speaking from experience on IR devices I would have a close look at the Raytek brand  8)

In food compliance we need +/- 1oC but for auto use +/-2oC is fine.

Has many uses, one is as suggested to determine naff thermostat OR if pulling a trailer (as I do from time to time) over long distances I use my Raytek to monitor wheel hub temperatures to ensure no bearing failures underway (I have a boat in regional Western Australia so distance is in multiples of 100kl) from experience with wheel bearings is 40 to 48 oC is AOK but higher than that you have a problem  :(

But wait theres more.... can use to monitor your fridge temp as those digital monitors in fridges/freezers have sensors positioned in optimal reading positions so i often find fridges at 7 to 8 oC  >:(

But your in Norway, freezing! had the privilege of visiting there in 2019 and OMG a great country, when this covid bollocks is done and dusted I'm going back there, found an awesome wine bar in Tromso  :-*

G
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 11 January 2022, 07:55 AM
I think I have you guys beat on low temps here in the Great White North.  Though I live in "balmy" Vancouver, places like Edmonton and Winnipeg can easily hit -50C with wind chill :o :o :o
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 11 January 2022, 10:31 AM
Although far north, Norway is blessed with the positive effects of the Gulf Stream -- a strong ocean current that brings warm water from the Gulf of Mexico into the Atlantic Ocean and later to the coast of Norway. Enables people to live here  :)

daantjie - Winnipeg and -50 deg C is hard to beat .... requires a coolant mix 100-0 I guess (water being the one digit number)  ;)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: goldacre on 11 January 2022, 03:20 PM
LOL  ;D

Today where I am it's +45oC  :-\ and we don't get ocean currents in my area, very hot Easterly winds swapping very hot westerly winds in the arvo  :'(

I did record -6oC on my windscreen ice sheet one winter, using my Raytek  :-*

Google Marble Bar, its in the North of Western  Australia,  that's hot.

All AU delivered W116 had the African rated Radiator, huge, I see the Euro W116 have the smaller one with oil cooler, think oil cooler was needed to allow the thinner oils back then to cope, but oil tech now is awesome.

G
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 13 January 2022, 12:56 PM
The coolant temp sensor was shot!

Installed a new today and let the car idle for 30 min. Temp rose to approx. 200 deg F (approx 90-95 deg C). Perfect!

A while back I cleaned, polished and tested the aux air valve (AAV). Worked 100%, hence I assume the AAV is fully closed (during test fully closed at 80 deg C).

Next step is to chase vacuum leaks .... with smoke? Any tips/experiences?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 12 February 2022, 09:05 AM
Vacuum leaks are on the agenda.

Tested the self-made "smoke machine" today. Got the tip from a guy on youtube.

It worked great until the soldering iron gave up on me, probably due to overheating.

I found a few leaks, see next post.

I need to find a "smoke machine" or buy a better soldering iron. Maybe dry ice .......
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 12 February 2022, 09:23 AM
Found a few leaks with the smoke machine, relatively easy. I guess it's among the usual suspects.

Leak 1-4 will be easy to fix. The two larger rubber parts - in and out aux air valve - I already have. Need to buy the 4mm and 5mm leak lines. And maybe the two small rubber parts on WUR.

Leak 5 will be a bit more challenging. The rubber hose with part number 100 090 01 82 is not easy to find? Any tips?

The injectors incl. seals are new and they looked fine. But I expect more leaks under the air intake.

The hunt continues as soon as the new "smoke machine" is in place.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 12 February 2022, 09:32 AM
Yup I would say that "100" hose will be a challenge for sure.  Likely NLA from Benz.  If the hose is still pliable you can try and put a hose clamp on that connection but likely it's rock hard from getting baked by engine heat.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: rumb on 12 February 2022, 10:19 AM
Might be real, might not:

https://www.eggmalltech.com/en/products/details/1389234.html

Somewhere in Thailand.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: ptashek on 12 February 2022, 11:33 AM
It's listed as available, and costs around 65EUR at Mercedes.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 12 February 2022, 11:45 AM
Fantastic, thanks to all of you!

I will check with MB on Monday.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 14 February 2022, 11:44 AM
Called MB today. The part is NLA.

Tomorrow I will call Mercedes Classics Center, last resort, before I start assembling a solution based on several individual hoses (elbows, reducing elbows, straight, etc.), will be a puzzle.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: rumb on 14 February 2022, 01:07 PM
Quote from: ptashek on 12 February 2022, 11:33 AMIt's listed as available, and costs around 65EUR at Mercedes.

https://partssearch.mercedes-benz-classic.com/parts/A1000900182?tt=automatic

Says no longer available.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: ptashek on 14 February 2022, 01:15 PM
That's a pity then. Hopefully you can get around it.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 26 February 2022, 10:22 AM
Disassembled the "100 090 01 82" hose today.

47 years old, hard as stone. No wonder there's a vacuum leak at that hose.

The hose is NLA, need to find a solution. I guess I will use several hoses with clamps. We'll see....
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 26 February 2022, 10:39 AM
I'll be following your progress with this hose for sure.  Can you do this with the fuel distributor and other crap in the way?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: rumb on 26 February 2022, 11:10 AM
If the hose is still solid you could try using plumping teflon tape on the fittings.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 26 February 2022, 01:25 PM
Quote from: daantjie on 26 February 2022, 10:39 AMI'll be following your progress with this hose for sure.  Can you do this with the fuel distributor and other crap in the way?

I had to remove 2 hard fuel lines on the right side, to get access. Relatively easy to remove, with all the rest in place.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 26 February 2022, 01:29 PM
Quote from: rumb on 26 February 2022, 11:10 AMIf the hose is still solid you could try using plumping teflon tape on the fittings.

Thanks for the tip, rumb. The hose is beyond repair - I need to find new hoses. A fix for the long-run.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 26 February 2022, 01:31 PM
Quote from: Jan S on 26 February 2022, 01:25 PM
Quote from: daantjie on 26 February 2022, 10:39 AMI'll be following your progress with this hose for sure.  Can you do this with the fuel distributor and other crap in the way?

I had to remove 2 hard fuel lines on the right side, to get access. Relatively easy to remove, with all the rest in place.

... and remove the fuel supply line to FD.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 28 February 2022, 03:45 PM
Still working on the vacuum leak. 5 leaks found.

New rubber boots, new vacuum lines, etc. ready to be installed. And gave the aux air valve. the idling house and bolts a thorough clean.

Waiting for 1 hose to arrive, and working on the solution for the "100"-hose.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 07 March 2022, 09:51 PM
I did some digging and looked at the hose on the 126.  Part number is 1160900882.  Looks a bit different and maybe length will not work but might be worth a gamble?
Google the part number and then pics come up.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 08 March 2022, 08:23 AM
Pic:

Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 08 March 2022, 03:39 PM
Thanks a lot, daantjie - fantastic effort!

I've spend a few hours googling tonight. There's a ton of breather hoses out there in all shapes and forms ... but not the "100".

The challenge is none of them have the inner diameter listed online. And I have some space constraints due to fuel lines.

I have looked at the 126-hose. If the inner diameters are ok I might be able to use parts of it inclusive hose connectors. But hose has to be cut. See pics and illustration.

I will call MB tomorrow and check if they can give me the specs of the 126-hose.

I also need a 3-way hose splitter. Found a brass splitter that should work. An alternative might be the hose splitter from the 126-hose.

To be continued ...
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 09 March 2022, 05:39 AM
... no information from MB regarding the hose specs (e.g. inner diameter).

Working on several options ...
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 09 March 2022, 09:13 AM
I wonder why the 126 hose has these ribs on it, maybe as insulation from touching the hot engine?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: goldacre on 09 March 2022, 12:17 PM
Ummm, thinking reinforcement ribs to stop it being sucked inwards restricting vacuum? And as a contact reinforcement?

G
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: raueda1 on 09 March 2022, 01:42 PM
The conditions under the hood are bad enough as it is, that's why all these parts eventually turn hard and brittle.  I'd therefore stay away from brass fittings to the extent possible.  Brass contains copper which promotes thermooxidative degradation of most plastics and elastomers unless specially formulated (which this stuff most certainly is not).  Cheers,
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 09 March 2022, 02:48 PM
Thanks, raueda1 - I didn't think of that.

One solution I'm following right now is to use a hose splitter made of nylon plastic. The temp range is up to 135 deg C (275 deg F).

Is that sufficient, what do you think?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 09 March 2022, 03:32 PM
Quote from: raueda1 on 09 March 2022, 01:42 PMThe conditions under the hood are bad enough as it is, that's why all these parts eventually turn hard and brittle.  I'd therefore stay away from brass fittings to the extent possible.  Brass contains copper which promotes thermooxidative degradation of most plastics and elastomers unless specially formulated (which this stuff most certainly is not).  Cheers,

I found a 3-way hose splitter made of stainless steel. Should be fine?
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 09 March 2022, 06:39 PM
Does anybody know exactly the function of this assembly?  To me it looks like it is a vent of sorts?  On the 126 it connects to a vent tube for the injectors. Hmm...
We need Aaron to school us here methinks 8)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 March 2022, 05:29 AM
daantjie,

yes that is also my understanding - a venting system. A small amount of gas from the combustion process "leaks" through the piston rings (more if the engine is worn out). It's also called "blow-by".

Many many years ago I had a Ford Zephyr 6 1964. On this engine these gases were released directly to atmosphere, through a cap on the valve cover (if I remember correctly).

A more environmentally friendly solution is to lead these gases back to the combustion chamber through the air intake.   
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: ptashek on 10 March 2022, 07:16 AM
Would an off-shelf fuel hose with a brass 3-way splitter not do the job? It looks like the hose is over-engineered for no good reason at all.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 10 March 2022, 07:48 AM
Yes, the current solution is an off-shelf straight silicone hose that can be bend (to some degree) under the FD + a stainless steel 3-way splitter + 2 x 90 deg hose bend + 2 x aluminum hose connectors.

The silicone hose can stand 185 deg C (365 deg F)

The one challenge I have is the reduction at idling house from 22mm to 5/8"mm with approx 22 deg bend (the inlet part of the hose). But I'm getting there .....
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: johnnyw116 on 11 March 2022, 02:41 AM
would an hose adaptor solve the reduction of the hose ?
something like this :  https://www.ebay.co.uk/itm/122049247077
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: raueda1 on 11 March 2022, 05:54 AM
Quote from: Jan S on 09 March 2022, 02:48 PMThanks, raueda1 - I didn't think of that.

One solution I'm following right now is to use a hose splitter made of nylon plastic. The temp range is up to 135 deg C (275 deg F).

Is that sufficient, what do you think?

Stainless and nylon are fine.  Just nothing with copper.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: hamidagha on 11 March 2022, 01:29 PM
Deleted as I posted to wrong thread! Sorry
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 13 March 2022, 12:49 PM
Quote from: johnnyw116 on 11 March 2022, 02:41 AMwould an hose adaptor solve the reduction of the hose ?
something like this :  https://www.ebay.co.uk/itm/122049247077


Perfect - thanks a lot!!!

Order already placed.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 13 March 2022, 02:14 PM
Thanks for your advice, raueda1  :)
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: johnnyw116 on 14 March 2022, 05:44 AM
Quote from: Jan S on 13 March 2022, 12:49 PM
Quote from: johnnyw116 on 11 March 2022, 02:41 AMwould an hose adaptor solve the reduction of the hose ?
something like this :  https://www.ebay.co.uk/itm/122049247077


Perfect - thanks a lot!!!

Order already placed.
i hope it solves the problem , it's hard to get stuck at such an simpel part like a hose 
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 14 March 2022, 08:03 AM
All required parts for the "self-designed" "100-hose" are on their way. Fingers crossed it will all fit  :-\  We'll know in 2-3 weeks (shipping takes so long  :'(  )

First part has arrived - the 3-way hose splitter! One down - many to go !
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 14 March 2022, 08:08 AM
Quote from: johnnyw116 on 14 March 2022, 05:44 AM
Quote from: Jan S on 13 March 2022, 12:49 PM
Quote from: johnnyw116 on 11 March 2022, 02:41 AMwould an hose adaptor solve the reduction of the hose ?
something like this :  https://www.ebay.co.uk/itm/122049247077


Perfect - thanks a lot!!!

Order already placed.
i hope it solves the problem , it's hard to get stuck at such an simpel part like a hose 

That hose almost drove me crazy! We'll see, I'm not at the goal line yet.
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: daantjie on 14 March 2022, 08:25 AM
Well if all goes well you can make a very limited side business to 6.9 owners ;D
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 14 March 2022, 01:28 PM
Quote from: daantjie on 14 March 2022, 08:25 AMWell if all goes well you can make a very limited side business to 6.9 owners ;D

 :)  LOL

I will post a pic with specs when the hose is complete.

Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 25 April 2022, 03:33 PM
I have been working on a "custom design" for the "100-hose". It took me 5 weeks and a few attempts.

The challenge is space constraints on top of the air intake and parts delivery time.

I believe this solution will work (see pic). Final assembly tomorrow. Knock on wood.

I need the car for a road trip in a week from now, hence the design of the lower left part of the hose is preliminary (marked with the red rectangle). I will replace that section with one piece oil-resistant silicone hose, custom made (see drawing), in a few weeks time. That means $$$, but it was very hard to find a suitable solution given the space constraints and required reduction. In the end I decided to pay $$$ to get the car on the road.

Tomorrow is the day ....
Title: Re: 6.9 K-jetronic rough and high idle cold start
Post by: Jan S on 27 April 2022, 03:30 PM
It worked - the self-made "100-hose" was installed yesterday, finally. Fired up the engine today. All fairly good, but idle is still high (900 rpm when warm). I guess it's a vacuum leak, somewhere.

Summary of what I have done last 6 months:
- replaced thermostat
- replaced engine coolant temp sensor
- cleaned idling house
- replaced all rubber boots and vacuum hoses around idling house and WUR
- replaced "100-hose"
- cleaned and tested aux air valve
- new injectors incl. rubber seals

The plan is to do a smoke test .... I assume there are some leaks under the air intake.

The chase for leaks continues, but first a road-trip in a weeks time.