Alright guys.
After weeks of delays, I got a fuel pressure test kit from Napa. It has a shutoff and a bleed valve, and a gauge that reads to 7 bar.
I was able to put a switch on the fuel pump too.
I'm having trouble however and hope I can ask the hive mind for help.
The way it's hooked up is that I have the tester between the large WUR fitting and the top of the fuel distributor. Picture attached.
With the valve open, I cycled the pump and bled the air out. I then shut the valve off, and the fuel pressure gauge shoots past 7 bar really quickly before I shut the fuel pump off. Am I doing something wrong or is something wrong with my 6.9 pressure regulator?
I have a feeling I have a return line issue
I have never done this before, but isnt the test with the engine running?
I did mine with motor running.
motor wont start... otherwise I'd do that.
System static pressure is way too high.
Not sure if you have the specs for US 6.9, but here it is. This is for WUR model 0 438 140 010 with full load enrichment but no altitude compensation:
System pressure: 5.0 - 5.6 bar
Control pressure engine fully warmed up: 3.4 - 3.8 bar
Full load enrichment (vacuum hose removed) at idle: 3.0 - 3.4 bar
Control pressure, cold engine with 20C ambient: 1.1 - 1.5 bar
Stabilization time @ 20C: 3 - 6 minutes
Hope this helps :)
Quote from: secondslc on 30 August 2020, 10:14 PM
I have a feeling I have a return line issue
Using some rubber hose, connect the fuel in and fuel out lines together and run the pump for a while.
Or use compressed air to blow thru the return line.
OK, let back up here for a moment.
Looking at prev posts your car was running.
When did it stop working?
I see you said "The two adjustments we were trying to dial in are the idle air screw and the fuel enrichment 3mm screw" The 3mm screw is the absolute last thing that should be touched and then very carefully.
If you have turned that screw a lot it may be very difficult to get back in range.
I would probably suggest sending the fuel distributor and WUR to CIS Flowtech for rebuild and setup. Once returned and following their instruction the car should run great. - You will still need to dial in the ignition timing.
This whole thing is a process. See if you can get ahold of the Bosch K-jetronic diagnostic manual. It lays out the whole process for this stuff from start to finish. There's a .pdf on the M100 site but I'm not sure if that's accessable. I'd email it but file is too big. It really ought to get added to the tech info here.
Anyway, let's start with basics. Before proceeding I suggest testing fuel delivery and return. You don't need to start engine. Disconnect the fuel delivery line and put into a collection vessel, about 1/2 gallon. Turn on ignition and unplug the blue socket and fuel pump will activate. Run the fuel pump for 30 seconds. If I remember right you should collect about 1 liter of fuel. If not then you need to fix that before doing anything else (clogged line, clogged filter, etc etc).
Next reconnect fuel line and disconnect the fuel return line and take gas cap off. Using compressed air check to be sure the return line is clear and unoccluded. You should hear bubbles in the fuel tank. You can be deceived by using much pressure which can blow air past a bottleneck in the return line.
If all is ok THEN test the primary pressure per Daniel's specs and your gauge hookup. It might be necessary to build WUR and FD, or it may not. Too early to say until you work through the process, so hold off for the moment. I'm traveling now, will provide more specifics on return early next week if you're still stuck. Cheers,
Ill start from scratch and go
From there.
The WUR is from kjet, the FD is rebuilt, the fuel pump is new, as is the filter, injectors, damper and the tank is cleaned out.
Also, i can blow through the return line.
Quote from: secondslc on 31 August 2020, 10:46 PM
Ill start from scratch and go
From there.
The WUR is from kjet, the FD is rebuilt, the fuel pump is new, as is the filter, injectors, damper and the tank is cleaned out.
Also, i can blow through the return line.
If all that stuff was done then you're probably not t0o far from OK. If you're shooting straight to 7 bar then yes, system pressure is obviously wrong, pointing towards the pressure regulator. However, if the FD was rebuilt then I'd assume was checked at the same time. But maybe not?
Though I can't be 100% certain, I suspect that the return line thing is actually very important. The line carries a lot of volume and if there's too much backpressure it would presumably increase the measured fuel pressure. Hence my emphasis on that. Others may chime in with better info.
Regardless, assuming fuel flow is OK (which it almost certainly is), sounds like time to check the pressure regulator. Unscrew it and inspect the o-rings, plunger and washers. Pressure is set by adding/removing washers and noting the effect. Rebuild kits are widely available, cheap and include washers. Tedious process - measure pressure, remove regulator, add/subtract washer(s), remeasure pressure, repeat. But if o-rings are NG then washers won't help. I'd just replace o-rings on principle. I have another thread here someplace on the pressure regulator, worth a search. If the skinny spring-loaded shaft isn't exactly right it will never be right. I got a new regulator and the shaft was about 1mm different from the original and it didn't work! Probably best not to disassemble the regulator body itself. I'll redouble my efforts to get the Bosch manual posted in the tech section. Stick with it and keep posting.... Cheers,
To be honest, the FD was pulled out of a box "as rebuilt" 20 years ago. It was sealed, but who knows WHO rebuilt it"
I fear I may have clogged the regulator by swapping lots of parts and maybe something going through at some point.
I pulled it, it had some stuff in it. But I also noticed the little o-ring isn't as new as it should be. Does anyone know the diameter for that? Is it "standard"? Its a cast iron FD
Are there more than one O ring?...I only see one?
Tomorrow I will run the fuel pump for 30 seconds and measure how much fuel gets pumped into a gas tank.
If its well below 1 liter, I have to start at the tank.
If its about 1 liter... then I move forward and find out why I have a return blockage.
Also, is my pressure regulator missing parts?
Images attached.
Make sure you keep a fire extinguisher handy ;)
Oh...and push the car outside too
It's pretty clear that the o-ring pictured is destroyed. Progress!! Replace it. There's also an o-ring on the regulator piston. The large spring goes into that but it often stays behind in the FD when removing the regulator. Get a stiff wire and insert into the bore and you should be able to fish it out. Be careful, obviously you don't want to scratch the bore. If it doesn't come out easily then you've identified a problem. There's an o-ring on that too and it should be checked or simply replaced.
If the regulator doesn't have any small washers on the shaft then yes, it's missing parts. They go between the larger spring and the regulator shaft. See this:
https://www.autohausaz.com/pn/11949622-F026T03010?utm_source=google&utm_medium=cpc&utm_campaign=feed_Mercedes&gclid=EAIaIQobChMI_eb-5snJ6wIVOx-tBh2ZhwcOEAQYASABEgL8UPD_BwE (https://www.autohausaz.com/pn/11949622-F026T03010?utm_source=google&utm_medium=cpc&utm_campaign=feed_Mercedes&gclid=EAIaIQobChMI_eb-5snJ6wIVOx-tBh2ZhwcOEAQYASABEgL8UPD_BwE) and this: http://www.bosch-classic.com/en/internet/bosch_classic/produkte/motor_1/systemdruckregler_1/systemdruckregler___mit_teaser_1.html (http://www.bosch-classic.com/en/internet/bosch_classic/produkte/motor_1/systemdruckregler_1/systemdruckregler___mit_teaser_1.html)
All those washers are used to set the pressure. If you don't have them just buy one of these kits. I don't think washers are available individually. Keep the progress, info and pix coming! Cheers,
and just a small anecdote about how screwy this stuff can be..... My car had a malfunctioning WUR. Rather than fixing the WUR somebody fiddled with the system pressure until they got it down to the control pressure. The car ran but the WUR wasn't really doing anything. Of course starting was hard, idle sucked etc etc. Point is, never assume. There seem to be a lot of people out there that take short cuts or have no idea. Just highlights the importance of starting at the beginning.
I have washers/shims, but i guess i have to dig in and get the rest of the regulator out.
Anybody have o ring specs?
Quote from: secondslc on 02 September 2020, 07:00 AM
I have washers/shims, but i guess i have to dig in and get 1. the rest of the regulator out.
Anybody have 2. o ring specs?
1. It's just that small piston and will take about 3 seconds once you know it's there. It's not tight. OTOH, if it IS tight then... :o
2. Sadly I do not and can't recall ever seeing them I think most folks just buy the kit. You could measure but maybe let the rings sit for a week or so (preferably in a vacuum oven, haha, cause we all have vacuum ovens sitting around, right?) for fuel to diffuse out so rings aren't swollen by fuel.
30 second test gave me more than a liter... but boy do i need better gas
Next step?
Yeah, the piston is JAMMED in tight. I don't know how it can come out without ruining the bore....
I'm going to go to NAPA tomorrow and ask if they have ideas, otherwise I have a spare unrebuilt aluminum FD I can throw on... But I really liked the cast iron one...
Ugh
Im just going to get a new FD, the aluminum one is used and the control plunger does not move freely.
Other than the gross fuel thats sitting in the car, everything will be new fuel system wise, and well... its easier to diagnose and tune at that point.
Quote from: secondslc on 04 September 2020, 07:07 PM
Yeah, the piston is JAMMED in tight. I don't know how it can come out without ruining the bore....
I'm going to go to NAPA tomorrow and ask if they have ideas, otherwise I have a spare unrebuilt aluminum FD I can throw on... But I really liked the cast iron one...
Ugh
Maybe try some heat if the FD is off the car. Localized heat from a propane torch can work wonders. Safety first of course. Could just be some gummed up fuel keeping it stuck.
I'll do this outside and what have i got to lose lol
Quote from: daantjie on 04 September 2020, 10:07 PM
Quote from: secondslc on 04 September 2020, 07:07 PM
Yeah, the piston is JAMMED in tight. I don't know how it can come out without ruining the bore....
I'm going to go to NAPA tomorrow and ask if they have ideas, otherwise I have a spare unrebuilt aluminum FD I can throw on... But I really liked the cast iron one...
Ugh
Maybe try some heat if the FD is off the car. Localized heat from a propane torch can work wonders. Safety first of course. Could just be some gummed up fuel keeping it stuck.
Careful though! Too much heat would likely damage the miniscule filters under the lines going to the injectors. Another possibiulity might be to shoot freeze spray inside the bore to shrink the cylinder after a good penetrant soak. Kind of mirror image of heating. It's worked for me before.
Secondslc: There is a silver lining here - if that cylinder is jammed you now know at least one sure cause of your crazy pressure There may be others too, but if that piston is stuck it's go-to-jail-do-not-pass-go! You might just want to go ahead and rebuild the iron FD. B ut if you go with the AL version note that the aluminum FD's have adjustment valves for each injector. Don't mess with them! Also, I'm pretty sure that lines and fittings are different. Not much maybe, enough to make installation very annoying. I'd discuss with CIS Flowtech and describe the problem and see what they think. Yeah, obviously you'll want new gas.... Cheers,
I'll get some freeze spray and a torch and play thermodynamics tomorrow
Is the FD still on the car? Maybe remove it to do this stuff. The fuel lines should come off easily enough and then it's just 3 screws. Then no fire risk.
Also, with all the fuel lines off you can rescue the tiny filters directly under the line couplings in case of too much heat. They should come out easily with a very fine wire.
If you take the FD off be VERY careful not to drop the central plunger. It can easily fall out. Then remember to put it back, as I learned the hard way.
Its been removed, I plan on only heating the pressure regulator section (may just use a heat gun) and then spraying the piston with freeze spray. It should give me the best chance
Freeze spray to the rescue... now... what size are the dang o rings
A good update..of sorts
Got new o-rings, and put it all together. Was able to adjust the fuel trim screw to where the fuel in the FD was not going up or down when the injectors lines were unhooked as per:
https://k-jet.biz/fuel-distributors/
-System Pressure is ~5.4 Bar
-With the fuel pump running... opening the valve, I get half a bar.
-Shutting the system off, the pressure shoots up to 2.4 bar or so, and then in 20 seconds drops to zero.
Is my accumulator busted?
After more testing...I put my old WUR In just to see what the difference would be.
System Pressure is within spec.
-Cold control pressure is .8Bar
-Plugging the WUR in, the pressure rises slowly, but only gets to 2 bar in 3 minutes.
-Leaving the valve open and shutting the fuel pump off, the gauge pressure drops from 2 bar to zero in one minute.
-Leaving the valve closed and shutting the fuel pump off, the gauge pressure drops to 3 bar pretty quick, but stays above 2.8 bar for well over a minute.
My question:
-What has my system control pressure so low?
-At what pressure will the injectors fire, cause now the car will not start...harumph.
I may be talking to myself, but at least it'll be documented ;D
Gauged the fuel pump itself by attaching the gauge to the supply line. Cycled fuel pump and wont stay above 4 bar, even then...it drops to zero after 20 seconds or so.
I think I have a bad check valve.
But would the bad check valve cause the control pressure to read low?
How sure are you your pump is good? If you have not yet replaced the pump (sorry too lazy on a Sunday PM to read the thread from the start 8)) I would for sure buy a new Bosch pump. They are not too pricey and will last the rest of the life of the car.
Pump is a new Bosch. Which annoys me that the check valve could be bad. But Im going to say grunge got into it and clogged it.
I ordered a check valve, accumulator, and fuel filter. I'm not gonna want to do this again.
I agree it's good to have a solid baseline so you can look at it from a process of elimination approach.
No, not talking to yourself (not yet anyway). Drove from S. Lake Tahoe to SLC yesterday and managed averaged of about 74mph including (frequent!) gas and rest stops. These cars like to go fast. Anyway, now that I'm home I've got the manual handy and can better summarize some of this stuff. These tests are in the specific order that Bosch specifies and numbered per the manual. Test 1 is throttle linkage adjustment and 2 is fuel volume.
3. Primary pressure test:
> hook up gauge and unplug electrical connector on WUR.
> CLOSE valve on downstream side of gauge
> turn on ignition (fuel pump will be off), then unplug fuel pump safety switch plug by the air intake (fuel pump should turn on).
> Read pressure. Should be in the region of 5.2-5.8bar. Need to look it up for your specific car.
> If you're not getting this then you need to adjust with the washers till you do.
> Now disconnect the fuel return line and plumb the fitting to a container. Retest pressure. It should be the same. If it's now lower then there's a restriction in the fuel return line.
4. Static pressure test
> Open the gauge valve
> turn on ignition, unplug safety plug and run fuel pump for 30 sec to fill the accumulator
> turn off ignition and read static pressure. It should be around 2.8bar and hold steady. After 30 minutes it should still be around 2.5bar.
> Causes of pressure loss include faulty primary pressure regulator, cold start valve, fuel pump return valve, accumulator and FD internal leakage. Can't hurt to replace the stuff you mentioned.
5. Fuel injector leak test - static pressure needs to be good before doing this
> With ignition OFF and with good static pressure...... Open valve on gauge.
> press air sensor plate down SLOWLY and observe gauge. It should move momentarily then return and hold steady. If not then an injector is leaking
6. cold start valve system test
Let's skip that for now and move on to . . . .
7. Cold control pressure test. If stuff above is all OK then it's time to try to start the engine.
> Open valve on gauge and unplug connector on WUR to keep it from heating up.
> Start engine and note system pressure. Pressure will depend on the WUR temp. I'll post a table, but at 77deg F it should be about 1.3-1.7bar.
> Shut it off and do NOT warm up the engine. Next test is aux air valve. If car is hot then you can't test it.
7. Aux air valve test
Let's also skip for now and return to the WUR......
8. Testing warm control pressure
> Open valve on gauge. PLug in WUR connector. Start engine and watch the gauge. Pressure should start going up as WUR warms up.
> Pressure should get to 3.4-3.8bar. This is with engine vacuum of 40mm Hg. If engine vac is lower 0.1bar and vice versa.
So, that's most of Bosch's process up to the point you're at. I suggest repeating it to see where you're at as each item relies on the previous item being correct. Hope this helps! Cheers,
Any progress?
Of all those tests, I do know that when I shut the system off, and keep the gauge connected, I drop to zero within a minute. There is no residual pressure.
I just got the accumulator, check valve, and fuel filter in the mail last night. It rained today. So I'll be swapping tomorrow and going through your list carefully after that.
Thanks for the help! and I'm glad you enjoyed your trip :D
The O ring in the piccie of the FPRV seems damaged.
Yep, I replaced it.
Alright, first things first. The Accumulator was original... or just old. It leaked fuel out the end, and looked grungy. I replaced it, along with the fuel filter. But Id didn't replace the check valve because the one that was sent to me had the wrong threads.... However, the Bosch fuel pump is new (was replaced before I got the car), and so I THINK the check valve is ok.
3. Primary pressure test was OK. In fact, with the accumulator replaced, the pressure went up slightly. I'll take it.
4. Static pressure test... well.. it never reaches anywhere near 2.8 bar with the valve open. This is where I'm stuck. However, I have a couple videos below.
As an aside, the system will bleed from ~3 bar to 2 bar over 30 minutes. This is improved from bleeding to zero within 30 seconds. So I did something right.
It seems with the valve open, I can't get to any sort of control pressure above .8bar.
Video one shows the valve closed and just system pressure. When I shut the fuel pump off, you hear two thunks, and the fuel pressure drops accordingly. It sounds like its the system pressure regulator bouncing. Could it be that I used the wrong o rings? I matched them up at Napa, but have the 100 dollar o ring kit from AutohausAZ I can throw in.
https://www.youtube.com/embed/p9i0Jg4tKDk
Video two shows the cold control pressure (gauge open). Pressure drops to zero pretty quickly after I shut the fuel pump off.
https://www.youtube.com/embed/Fd5c3pn0tTg
Video 3 shows the WUR doing it's thing
https://www.youtube.com/embed/Ew1jM09Naac
Hi SecondSLC. I notice in your photo of fuel pump assembly, it has the somewhat elusive and mysterious plumbing that Benz identifies as "Pressure Compensator". This is the small line that taps off the inlet connection of the filter, that connects to the "Compensator" doodad that is under the center of the mounting bracket, which then connects into the leak off line of the accumulator. The Mysterious part about is that there is no mention in the Benz service manual, at least none that I have found. It is my assumption that it is a type of Pressure Regulation Valve that prevents over pressure in the system, that dumps back into the suction side of the pump assembly. You related that your pressure does not achieve specification. It may be that this "Compensator" is compromised, and is recirculating partial pressure back to the pump inlet. This "Compensator" circuit was eliminated in later versions of fuel pump assemblies. It's just a thought. Hope this helps. JM Sr.
Oh, I was assuming that system was a "don't touch it". But now wonder if it can somehow be removed?
As an aside, the car still wont start. But I fear I have wet spark plugs, or something else is going on. I need to re-visit the check valves in the vacuum system, as well as the lines themselves. I replaced all of them, and verified their accuracy, but I can still be wrong.
I don't know if it can be eliminated without changing other components. The accumulator and possibly the pressure regulator at fuel distributor could be calibrated for it. Another part of its mystery, owing to not having a definite explanation of it's purpose other than one's own conjecture. Benz spent the funds to include it at first, but obviously eliminated it later in production. Another part of the fun of older cars ! JM Sr
Not sure if any of this is helpful, but this is how the two different assemblies are shown in Xentry.
The one with the two output-port accumulator is shown as being used up-to chassis #5693, the other one after #5693.
Quote from: secondslc on 12 September 2020, 08:09 PM
Alright, first things first. The Accumulator was original... or just old. It leaked fuel out the end, and looked grungy. I replaced it, along with the fuel filter. But Id didn't replace the check valve because the one that was sent to me had the wrong threads.... However, the Bosch fuel pump is new (was replaced before I got the car), and so I THINK the check valve is ok.
3. Primary pressure test was OK. In fact, with the accumulator replaced, the pressure went up slightly. I'll take it.
4. Static pressure test... well.. it never reaches anywhere near 2.8 bar with the valve open. This is where I'm stuck. However, I have a couple videos below.
As an aside, the system will bleed from ~3 bar to 2 bar over 30 minutes. This is improved from bleeding to zero within 30 seconds. So I did something right.
It seems with the valve open, I can't get to any sort of control pressure above .8bar.
Video one shows the valve closed and just system pressure. When I shut the fuel pump off, you hear two thunks, and the fuel pressure drops accordingly. It sounds like its the system pressure regulator bouncing. Could it be that I used the wrong o rings? I matched them up at Napa, but have the 100 dollar o ring kit from AutohausAZ I can throw in.
https://www.youtube.com/embed/p9i0Jg4tKDk
Video two shows the cold control pressure (gauge open). Pressure drops to zero pretty quickly after I shut the fuel pump off.
https://www.youtube.com/embed/Fd5c3pn0tTg
Video 3 shows the WUR doing it's thing
https://www.youtube.com/embed/Ew1jM09Naac
The videos are great. Still, let's clarify a little. Something seems inconsistent here..
Video 1: Ignition is on, fuel pump is running - pressure drop/increase change results from closing/reopening the gauge valve, right? IOW, what did you do to get the 2.9 bar reading? Was WUR plugged in and hot? 2.9 is low, but still not
so very far off from 3.4-3.8 spec.
Video 2: Is this what happens when you do Bosch test 4?
Video 3: yes, that's what the WUR ought to do when you plug it in, more or less. Seems like both cold and warm control pressures are on the low side. But if all else is good these can be adjusted.
Maybe you could reframe your results per the Bosch test sequence. Would be easier to follow. That's always the challenge when threads start growing. :P Don't despair. Eventually you'll get it licked.
I'm an engineer, this is a machine, there HAS to be a solution! But I'm also a little frustrated/excited, so I apologize if I'm not easy to follow, I'll keep trying to sort this out.
I only did test 3 and 4 of the Bosch test sequence, and tried to comment on results for those. But I can try and explain further :-).
Video 1: Bosch Test 3 Ignition is OFF. I have a switch to the fuel pump. No WUR involvement here. The 2.8 reading is the accumulator seemingly doing it's job and holding pressure. As an aside, I replaced the system pressure valve seals and assembly with a new one, doesn't seem to thunk as much.
Video 2: Sort of test 4, now that I read the procedure more I should repeat it. In this video, I had the ignition OFF, test valve open, and ran the pump. Pressure never went above .8 bar, and then I shut the pump off, and you can see the results. This test needs to be repeated with the ignition on, but I don't think I'll get a different reading.
I hope this is sorta clear.
Not to muddy the waters too much...but here is a generic KJET troubleshooting guide, might be helpful:
Troubleshooting K Jetronic
Engine turns but won't start
1) No fuel pressure;
Test the fuel pump and do a fuel pressure and volume test.
2) Jammed and/or sticking airflow sensor;
Relieve resting fuel pressure by pulling fuel pump relay and starting car and run until it dies.
Press down on the center bolt of the round plate and you should feel no resistance or binding and should return to top rest position. Also check that the rest height and centering are correct.
3) Auxiliary valve is sticking;
4 )Defective cold start injector;
If the injector does not function, the air-fuel ratio will be lean, preventing easy start up.
5 )Shorted or defective thermo time switch;
The cold start injector will not work if the thermo
time switch is defective. Check this in the event that your cold start injector does not function before replacing.
6) Control plunger sticking;
Remove the fuel distributor from the airflow sensor and check to see if it moves freely.
7) Restricted injectors;
For this to be the cause, they would have to be severely restricted, which is why I listed it last. Do
an injector flow test and ensure that the delivery is
near equal.
Hot starting difficulty
1) Loss of rest pressure;
Do a pressure test and focus on the rest pressure. If
it does not pass, check for a defective fuel pump check
valve, defective fuel distributor, faulty system pressure regulator and leaking cold start injector.
2) Airflow sensor adjusted incorrectly;
Check height, centering and for binding. Remove the boot and loosen the center line on fuel distributor to
relieve control pressure.
3) Sticking or binding of the control plunger;
Remove the fuel distributor and ensure that the control plunger moves freely.
4) Injectors leaking;
Remove the injectors from the intake manifold and with the ignition key on/engine off, press on the center plate to pressurize the system. Inspect and replace any injector that is leaking.
5) Cold start injector leaking;
Same test as above.
6) Shorted thermo time switch;
Cold start injector is dependent of this component.
7) Incorrect control pressure;
Do a pressure test and verify that the warm control pressure is within spec.
Rough idle (cold)
1) Cold control pressure incorrect;
The movement of the control plunger will be limited if the cold control pressure is too high. This in turn will limit the amount of fuel able to be delivered through the injectors. The result will be a lean ratio and will cause rough idle.
2) Auxiliary air valve defective;
If defective and not opening, idle cannot rise and results in rough idle.
3) Airflow sensor adjusted improperly or binding;
If the movement is not smooth, it will result in air-fuel ratio errors.
4) Leaking cold start injector;
If the cold start injector is leaking, the engine will be over fueled even if cold. If the cold start injector is leaking, the idle will get worse as the engine temperature increases.
5) Injectors have an unequal flow or spray pattern;
Do an injector flow test and replace any that do not deliver the correct amount of fuel or have a poor spray pattern.
Runs rough (warm)
1) Warm control pressure incorrect;
Incorrect warm control pressure that is too high or low will cause an incorrect air-fuel ratio, thus resulting in a rough idle.
2) Airflow sensor adjusted improperly or binding;
If the movement is not smooth, it will result in air-fuel ratio errors. Check for centering and correct rest height.
3) Leaking cold start valve;
Again, will result in over fueling the engine, resulting in a rough idle.
4) Injectors have an unequal flow or spray pattern;
Do an injector flow test and replace any that do not
deliver the correct amount of fuel or have a poor spray pattern.
Stalls after starting (warm)
1) Warm control pressure;
If the warm control pressure is too high, the air-fuel
ratio will be lean.
2) System pressure incorrect;
If too high or low, the air-fuel ratio will be incorrect.
Idle speed high
1) Check auxiliary air valve;
Ensure that it is closing.
2) Vacuum leaks;
Self-explanatory.
3) Check the minimum air;
Self-explanatory.
Backfire in intake
1) Check that CO adjustment is correct;
If incorrect, backfire will result if started and under a load.
2) Boot between airflow sensor and throttle defective;
Will result in a lean mixture due to secondary air(false air)
3) Vacuum leaks;
Self-explanatory.
Misfires
1) Ignition;
Inspect the cap, rotors, wires and plugs.
2) Fuel delivery inadequate;
Check for binding of airflow sensor, control plunger,
incorrect control or system pressure and restricted injectors.
3) Injectors;
Unequal delivery or poor spray pattern. Do a test and
replace any that are defective.
Poor power
1) Control pressure too high;
If the control pressure is too high, the control plungers travel will be limited, resulting in a lean running engine.
2) Check ignition components;
Verify that the spark plugs,wires,cap and rotor are not worn.
3) Injectors restricted;
Do a test for delivery. If an injector is restricted, fuel delivery will be limited, thus power will suffer.
Sag or stumble when accelerating
1) Airflow sensor plate binding or sticking;
If binding or sticking, fuel flow will be limited.
2) Control plunger binding or sticking;
If binding or sticking, fuel flow will be limited.
3) System pressure or warm control pressure incorrect;
If too high, the travel of the plunger will be limited.
4) Injector flow unequal;
Self-explanatory.
Fuel consumption high
1) Air-fuel ratio incorrect
2) Injectors leaking
3) Cold start injector leaking
This helps..sorta but now I have questions lol
Thermo time switch...thats the connector in the WUR?
And how do I know if my air plate height is correct? Am I adjusting it when the car is off or when the pump is running? Could it be that its letting too much air in?
Nope the thermo time switch screws into the block (passenger side at firewall) and senses the temp, which then signals to the cold start injector to fire for a certain time. It should only affect cold start performance, and should not fire at all after the motor is running, after the set amount of time (based on the temp) has elapsed.
Usually if the injector itself is faulty it will keep dumping fuel, which will lead to rough running as you are then overly rich.
ah, ok.
It cranks and cranks and cranks, chugs one and then keeps cranking.
Kind of annoying as I used to start right up WITH a bad accumulator
Can you use a timing light when turning it over to see if it is in range. Make sure the disti has been put back in the correct position. You can also then turn the disty while cranking, try advancing it.
fuel+spark;timing = engine start
check plugs after trying and see if they are gas wet.
Friend and i spent a sunday getting the timing perfect after rebuilding the distributor. Advances as it should too. im suspecting wet plugs. I also want to check vac lines.
Quote from: secondslc on 15 September 2020, 06:52 PM
Friend and i spent a sunday getting the timing perfect after rebuilding the distributor. Advances as it should too. im suspecting wet plugs. I also want to check vac lines.
Yes, do check vac lines. Essential. If you got a leak all the rest is in vain. That said, if engine doesn't run you can't really check advance. Or was this when engine WAS still running?
Anyway, I feel your pain. I've been there (and far worse). I'm the world's expert at taking something works OK and making it not work at all. So PM your email to me. I finally got the manual on dropbox and I'll send you the download link. Then read it through about 20x and start at the beginning and work through it. Just don't jump around or skip tests. You'll only mislead yourself. For the system to work EVERYTHING needs to work and there's a sequence to do that. Hang in there and cheers,
It's funny, my first cars were motronic VWs, then I bought a 5 cylinder turbo CIS Audi and SWORE I'd never touch CIS again. I then rebuilt and restored a motronic turbo 5 Audi, and then moved to the M120 Merc. I did the front timing covers and put the damn thing together from memory without an issue (I did look up torque specs).
But this, this car... man this car makes me doubt all the years I spent on the easy stuff!
Regarding the vac lines..
I was meticulous in mapping everything according to the diagram I thought best represented a 1979 California 6.9 (attached diagrams if anyone wants to look). Im a EE by trade and have built stereos point to point via diagrams. I'm pretty OK with diagrams...however. I am still iffy on the WUR and check valves as per these pictures. I can't tell which way the valve should go as the image quality is not great. I am also told the vac port on the top of the WUR is the port I should hook manifold to...and the bottom should be to atmosphere.
Regarding the timing... It was set with the car running. Apparently the car was running on hopes and dreams at that point as my accumulator was bad, and the system pressure control system was stuck. I honestly don't know how it ran so well.
Regarding what happened between the car running and now...
I changed the air meter assembly as the adjustment screw fell out (long story, at least the car was off and I learned a lesson). I put another air meter assembly in and I adjusted the 3mm Allen screw to a baseline to where no fuel came out while the metering plate sat neutral and the pump was on. Thats when it stopped starting. But thats also when I decided to measure with gauges, and when I found the stuck system pressure valve, bad accumulator, and learned a lot about how it all works.
At this point, I am thinking maybe my 3mm screw is set a little too lean and the injectors are not firing when starting. It ignites and REALLY wants to start every time I try it for the first time after a few hours. It seems the cold start injector is firing, giving it enough gas to ignite..and thats it.
However, I'll PM you and start with the manual...in order. And in the daytime when I am a bit more rested and a bit less weary.
I do want to thank you guys for sticking through this, slowly but surely its coming back to life.
Hi
After reading your last part of the story where 3mm mixture screw fell etc I bet that's why it's having difficulties starting.
Insert the 3mm key. Move it clockwise in increments of 1/2 turns. Count every time you turn. You don't want to lose your current mixture baseline. Cranck, 1/2 turn, crank, 1/2 turn.... up to 10 turns, no more. Any changes?
If no joy, go back to baseline and repeat but anti-clockwise. Nothing?
Check frequently one or 2 spark plugs to avoid a flooded engine. Check oil stick frequently for gas down there.
If the above trick doesn't work, do the following to identify a good baseline for the 3mm mixture screw.
I would remove the gauge momentarily and re-hook up every to rule out gauge issue (seen that before).
Ignition on, push the meter plate about 1mm down. You should hear the pump run. Turn the 3mm screw starting anti-clockwise until you hear a distinctive high pitch noise (is the injectors opening). Stop right there. That's your baseline. Repeat clockwise but careful not to drop that screw down again.
Lastly, check the 2 ballast resistors for continuity and resistance (0,4 and 0,6).
As mentioned earlier check that distributor cap again. I know it's too basic but check you're getting spark out of the coil and to at least 1 spark plug.
Come on buddy, you're almost there, that engine was running fine it WILL start again don't worry.
Another too-basic yet important check. By any chance when recovering the 3mm screw did you unplug some of the spark plug cables for better access? Maybe a couple got mixed up during reassembly? Just saying... seen that too on V8s like yours as the FD isn't far.
The fuel gauge is essential to fine tuning correctly, no doubt. But you need the engine running (even rough) first. You haven't touched your WUR setup and the engine WAS running so forget about the gauge for now until you have the engine running. The fact the engine was running tells us your control pressure (controlled by the WUR) is not far out to at least the engine gives signs of combustion action,
I bet again it's the 3mm mixture off by far after reading your story that it fell etc.
Good luck
Today I verified residual pressure.
I then turned the screw 1/4 turn and tried starting, it caught and sounded like it was going to start, but did not. The timing and ignition system is ready to go, I trust that part of the system.
Then I turned it half a turn at a time, for a grand total of 14 turns. I could hear the injectors firing as I cranked.
Then I pulled the plugs, all of them are soaked evenly, and they're all past their prime (I knew this).
Could they have finally given up the ghost even tho it seems to really want to start when cold? At least I know they're all evenly wet and all evenly awful.
Going to let the thing air out overnight and wait for some comments.
Sounds like you're on the right track.
I'd get rid of those platinum plugs and fit normal non resistor ones. They're not a suitable plug for these engines.
Tim
I'm going to do just that, and crank the fuel screw back to baseline. No reason to foul the next set of plugs.
Is there a plug to get? Or just what MB used back then?
I use NGK BP5ES on my 6.9, works great.
RE: Spark Plugs. In 1975 when 6.9s began rolling of the line, Euro market cars came out with Bosch W 200 T30 which was later renumbered W 6, U.S. market cars starting in 1977 used Bosch W 125 T30 which was later renumbered W 9 D, then to W 9 DC (copper core), then to 7511. The 200 Euro plug has colder heat range for sustained high speed driving. The U.S. 125 plug (W 9 DC) has a hotter heat range for stop and go driving. W 9 DC plugs are pretty common on EBAY at various prices. For What It's Worth....JM Sr.
I think a lot of us here happily run the NGK BP5ES or BP6ES, depending if you want a colder/hotter plug.
If you go to the MB parts desk, you'll get a re-packaged Bosch plug. Either a W9 or a W8, can't remember which exactly.
An update...
-New plugs in, no start. Bollocks
-Noticed the air meter plate was not moving when cranking. (I was a fool and adjusted it to have a bit of a gap before installing it.) Took it all apart and adjusted it per the manual. While I was in there I made sure the fuel mix screw was adjusted so that the 8 FD ports had fuel in them but would not move. Thats baseline. No start... damn
-Counted and cranked the screw in half a turn at a time as the plugs were dry. Turned it till the plugs were wet. No start.
Alright, so now I knew I was getting fuel, and I know the metering plate is moving when cranking. I also knew the timing was right and the entire ignition system was rebuilt...except the wires as I wanted to find the right ones... So I inspected and noticed the coil was warm...
Pulled the coil wire, adjusted the fitting. And here is the result.
https://youtu.be/OmSpmBpd3oM
;D
I adjusted the fuel to about a quarter turn past baseline and it no longer popped or missed. Seems to rev freely, and knowing what I know now... the fuel system is "perfect"
Next up
-An oil change as I have probably destroyed the oil in it.
-New ignition wire set
-I need to replace the rear leveling arm, as it broke during the fuel pump replacement, and I currently am set at full stiff, can't drive it.
-My cats smolder after a few minutes of running the engine above idle. The insulation starts smoking and well... it's a cause for concern as they cook the interior too. They're either clogged or extremely full of fuel. Either way, check out the awful mess coming out of my tailpipe.
-When I take the car in to inspect the cats...I am going to have two Wideband bungs welded in pre-cat so I can understand the tune. Seems like a much more reliable way of testing than an exhaust sniffer.
Then it's on to brake lines and tires. Aged rubber is going to be my next fun chase!
Guys, I was ready to give up on this thing, thanks for the encouragement, and convincing me I was so close. I'm still a ways from "finished", but at least the car feels alive.
Niiiiice ;)
Awesome! Persistence and patience paid off. Looking forward to your next adventures. Solid!
Glad to hear it is sorted now. Well done!
Awesome !! It's always the simple things that can stump you ! Good job !! JMSr
Bravo!!!
As somebody said before, and before, and before... spark + fuel + igt timing + mixture ratio = combustion and running engine. It's simple at the end of the day. Good job.
Now you can hook up your gauge to fine tune the system. If I remember correctly you had 0.8 bar cold control pressure. Hope I'm not confusing. That's a bit low/rich at 20C but within range per spec. Most importantly, if it reaches 3.6-3.8 bars within 3 minutes when hot it's ideal. For that the WUR has to be revisited (if needed). Let us know of next steps in case you need help.
Cheers
Thanks guys!
Bit of a hiccup, the fuel pump in my sl600 failed... lol. Guess it got envious