Author Topic: Exact fuel pressure test hookup help needed for a California 6.9  (Read 1101 times)

raueda1

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #45 on: 14 September 2020, 05:09 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.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #46 on: 14 September 2020, 07:17 PM »
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.
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

daantjie

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #47 on: 15 September 2020, 10:23 AM »
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
Daniel
1977 450 SEL 6.9 - Astralsilber

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #48 on: 15 September 2020, 11:14 AM »
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?
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

daantjie

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #49 on: 15 September 2020, 11:18 AM »
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.
Daniel
1977 450 SEL 6.9 - Astralsilber

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #50 on: 15 September 2020, 11:26 AM »
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
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

rumb

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #51 on: 15 September 2020, 04:32 PM »
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.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #52 on: 15 September 2020, 04:52 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.
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

raueda1

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #53 on: 15 September 2020, 05:35 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,
« Last Edit: 15 September 2020, 05:50 PM by raueda1 »
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #54 on: 15 September 2020, 06:25 PM »
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.
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

revilla

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #55 on: 15 September 2020, 09:34 PM »
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.
Robert
W116 1977 280SEL & 1979 280SE

revilla

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #56 on: 15 September 2020, 09:51 PM »
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
Robert
W116 1977 280SEL & 1979 280SE

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #57 on: 16 September 2020, 04:16 PM »
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.

1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

TJ 450

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #58 on: 16 September 2020, 07:29 PM »
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


1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

secondslc

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Re: Exact fuel pressure test hookup help needed for a California 6.9
« Reply #59 on: 16 September 2020, 07:43 PM »
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?
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8