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 6.9 running like crap
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arcijack

USA
450 Posts

Posted - 10/10/2016 :  21:51:01  Show Profile  Reply with Quote
got issues with my 6.9, i took it out for a spin Sunday, and it started running bad, idle was terrible, back firing throughh intake, changed fuel dist to alloy dist i had laying around, car fired up and ran like a scalded dog, drove about 3 miles and it literally came to a crawl, wold not drive over 10 miles per hour when i tried to give it gas it shut down, but always manage to start, after several stops i would tap on fuel dist and it would fire right up idles ok and do the same thing after a short drive, it took me and hour to get home from a 5 mile distance, i have been at this thing for a week trying to figure out what is wrong, i did a system test, right on spec 5. 6 bar, control test same as system 5.6, after shutting off engine the pressure drops to 0 in 10 minutes , not a slow drop but a fast drop. i dont drive this car much, around the block or so every 2 to 3 weeks, any suggestion is appreciated.
thanks Arcijack

daantjie

Canada
890 Posts

Posted - 10/10/2016 :  23:13:47  Show Profile  Reply with Quote
Failed fuel pressure damper or accumulator perhaps?

Daniel
1977 450 SEL 6.9
Vancouver, BC
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RANDYS

Australia
487 Posts

Posted - 10/11/2016 :  01:04:01  Show Profile  Reply with Quote
Oh my favourite subject!!

Very rarely can u pick up a part that's an unknown quantity and plug it into the system and hope like Hell you jagged the right component. The fact the fuel pressure falls rapidly is not right, but it is probably not why it runs like a dog.

Swapping out fuel distributors is a pain so u want to be damn sure what you are putting in is a 100% goer.

Can I just query you on a value you quoted.?

i did a system test, right on spec 5. 6 bar, control test same as system 5.6,

System pressure is 5.6 bar but hot control is closer to 3.6 Is this a typo? If not there's your problem!!
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S class

South Africa
943 Posts

Posted - 10/11/2016 :  03:26:45  Show Profile  Reply with Quote
Indeed, that control pressure is too high, and suggests a blockage in the WUR, or the lines to and from the WUR.

What you can do is while running the engine with the gauge installed, crack open the line going into the WUR at the WUR just slightly and see if the pressure drops. IF it does, the blockage is then in the WUR or its return line. Then try cracking open the return line at the WUR and then at the FD to try and narrow down where the blockage is.



116.036 - trusty rusty
116.036 - Rooikat
116.024 - the merc
116.028 - Penelope
116.032 - Esmeralda
126.037 - Scheckter
126.037
107.046



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arcijack

USA
450 Posts

Posted - 10/11/2016 :  07:58:14  Show Profile  Reply with Quote
yes the control pressure is reading 5.6
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ctmaher

USA
666 Posts

Posted - 10/11/2016 :  11:59:53  Show Profile  Reply with Quote
Check for a blocked return to the fuel tank.

Chris
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Clayton

USA
55 Posts

Posted - 10/11/2016 :  20:24:21  Show Profile  Reply with Quote
Speaking of blocked return line, every time I remove the gas cap, there a vacuum sound. Is that normal?










































































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Ron B

Australia
11545 Posts

Posted - 10/12/2016 :  03:06:27  Show Profile  Visit Ron B's Homepage  Reply with Quote
Nope. A pressure release sometimes in hot weather is normal . You have a blocked tank or tank vent (someone played with the emissions system?).What is possibly happening is that your pump is pulling enough fuel to keep the car running then once it starts pulling a vacuum the volume of fuel drops off too far to keep the CIS working.Hence the lean condition indicated by the back firing through the intake. (you need 3.6 bar to keep the injectors running) but if you also have a blocked return the CIS is fighting a high pressure which makes acceleration sluggish. Try aiming the fuel return line into a container and watching your pressures . if the car revas easier,you may be ahead of the game by removing and replacing the tank.

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section

Edited by - Ron B on 10/12/2016 03:07:39
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karra

Finland
855 Posts

Posted - 05/11/2017 :  09:30:23  Show Profile  Reply with Quote
My 6.9 was already last summer behaving oddly. Cold running was a problem, and driving was crappy before the engine was fully warm. Last weekend I had to start at a hotel, it was -1 deg C outside. The car started but died immediately, I had to repeat 10 times before it stayed running; no way to drive as it stalled when I touched the gas pedal.

As well I felt the acceleration was poor, I mean the response to throttling when driving fully warm.

I disconnected the WUR fuel lines and cleaned the return line with compressed air through the damper to opened end at the fuel distributor. I think there was something clogging the line as the air did not come out immediately.

I cleaned the WUR connections also, and used brake cleaner and in the end I sprayed carburetor cleaner there and let it soak for 15 minutes.

Anyhow, after re-installing all worked well; the cold idle went to 1500 rpm and the motor responded well. It warmed up and idling dropped to usual numbers. The exhaust noise sounded nice, much stronger and it was very smooth - like the car was when I got it.

Today I will do the cold start again and will make a test run. Anyhow it look promising, the response to gas was much better also when warm - test drive will tell the difference.

Kari Pykäläinen

1971 300 SEL 6.3 #5581
1980 450 SEL 6.9 #7201
1987 560 SEC
1992 500 E
2000 G500

http://suomi.mercedes-benz-clubs.com/
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daantjie

Canada
890 Posts

Posted - 05/11/2017 :  12:49:17  Show Profile  Reply with Quote
Again just proves that K Jet needs pristine fuel and solid supply of fuel to run nicely. As you did Karra always start simple with a good clean of all lines, BEFORE messing with WUR and FD rebuild. If it is not getting good fuel to begin with it will NEVER run right no matter how much you fiddle with the WUR and FD.

Daniel
1977 450 SEL 6.9
Vancouver, BC
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karra

Finland
855 Posts

Posted - 05/13/2017 :  16:39:50  Show Profile  Reply with Quote
Well, the next day trial did not go well; the start at cold and the cold running was bad again.

Next day I decided to go on a bit further. Reason was that when I blew the pipe backwards with compressed air towards the fuel distributor the air went into the opening and I saw some dirt coming out. I used the air gun directly into the fuel distributor top connection and white colored sludge came out.

I also cleaned the WUR again and installed rubber hoses on it and filled those with carburetor cleaner and soaked overnight.

I saw the strainer at the control pressure fitting on the WUR but could not get it out. There was some black dirt on it.

Anyhow today I blew it with air backwards several times having filled it with cleaner in between.

Test run showed it worked well, I drove some time until the motor was fully warm. I can feel a functional WUR makes a difference in driving. I hope it works now, but tomorrow will show...

Kari Pykäläinen

1971 300 SEL 6.3 #5581
1980 450 SEL 6.9 #7201
1987 560 SEC
1992 500 E
2000 G500

http://suomi.mercedes-benz-clubs.com/
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Ron B

Australia
11545 Posts

Posted - 05/14/2017 :  05:49:02  Show Profile  Visit Ron B's Homepage  Reply with Quote
Mm, sounds like a new filter in the tank and pump filter should be next .if you have plumbing camera, check inside the tank to make sure it is rust free.

The white sludge is fuel and water mixed together which become acidic and eats ally parts. The black dirt could be fine rubber particles from the inside of the fjuel hoses as they decay.Something else to change.

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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karra

Finland
855 Posts

Posted - 05/14/2017 :  12:33:48  Show Profile  Reply with Quote
The first thing I did with the car was replacing all the rubber fuel hoses in the car, also the fuel filter along with the strainer at tank. There was no dirt seen during this work.

The first summer I drove the car I was checking some other things before I was going to replace the fuel injectors, I actually reported here also that I drove 500 km with a fuel mixture of 70% gas and 30 ethanol, to clean all up. It was poor to drive and got worse as the trip proceeded, anyway I got back home and filled the tank with normal gasoline, later on I replaced the fuel injectors and the engine started to run fine.

Later on I noticed this bad cold behavior plus hesitation when accelerating.

So it could be my ethanol test or perhaps the gas that was used in Las Vegas - I do not know how much ethanol they have there. I have been buying my gasoline in Russia for 22 years now and they have ethanol-free gas there which is good.

Is the construction of fuel distributor such that there can be water-emulsion trapped in the top chamber? Seems the water was sitting there in the bottom part and the control pipe connection is at the highest position there.

Kari Pykäläinen

1971 300 SEL 6.3 #5581
1980 450 SEL 6.9 #7201
1987 560 SEC
1992 500 E
2000 G500

http://suomi.mercedes-benz-clubs.com/
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daantjie

Canada
890 Posts

Posted - 05/14/2017 :  15:24:36  Show Profile  Reply with Quote
quote:
Originally posted by karra

The first thing I did with the car was replacing all the rubber fuel hoses in the car, also the fuel filter along with the strainer at tank. There was no dirt seen during this work.

The first summer I drove the car I was checking some other things before I was going to replace the fuel injectors, I actually reported here also that I drove 500 km with a fuel mixture of 70% gas and 30 ethanol, to clean all up. It was poor to drive and got worse as the trip proceeded, anyway I got back home and filled the tank with normal gasoline, later on I replaced the fuel injectors and the engine started to run fine.

Later on I noticed this bad cold behavior plus hesitation when accelerating.

So it could be my ethanol test or perhaps the gas that was used in Las Vegas - I do not know how much ethanol they have there. I have been buying my gasoline in Russia for 22 years now and they have ethanol-free gas there which is good.

Is the construction of fuel distributor such that there can be water-emulsion trapped in the top chamber? Seems the water was sitting there in the bottom part and the control pipe connection is at the highest position there.

Kari Pykäläinen

1971 300 SEL 6.3 #5581
1980 450 SEL 6.9 #7201
1987 560 SEC
1992 500 E
2000 G500

http://suomi.mercedes-benz-clubs.com/



Karra does yours have the fuel evaporation system in place which circulates the fumes from the tank back into the intake system via the charcoal canister? Probably not that but maybe you are getting water/vapour ingress into your fuel via this system?

Daniel
1977 450 SEL 6.9
Vancouver, BC

Edited by - daantjie on 05/14/2017 15:25:33
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karra

Finland
855 Posts

Posted - 05/14/2017 :  23:19:02  Show Profile  Reply with Quote
quote:
Originally posted by daantjie

[quote]
Karra does yours have the fuel evaporation system in place which circulates the fumes from the tank back into the intake system via the charcoal canister? Probably not that but maybe you are getting water/vapour ingress into your fuel via this system?

Daniel
1977 450 SEL 6.9
Vancouver, BC


Hi Daniel, no I have removed the canister. I believe the sludge is formed by ethanol and water over time like Ron said and as it is heaver than gasoline it can stay there just on top of the control plunger.



And, forgot to say but on the next day the car ran well, so now it seems that the problems is over.

Kari Pykäläinen

1971 300 SEL 6.3 #5581
1980 450 SEL 6.9 #7201
1987 560 SEC
1992 500 E
2000 G500

http://suomi.mercedes-benz-clubs.com/

Edited by - karra on 05/14/2017 23:20:44
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karra

Finland
855 Posts

Posted - 06/12/2017 :  10:55:03  Show Profile  Reply with Quote
Well, the bad cold running and hesitation at warm came back. I soaked the WUR with another brand of carb cleaner for a week and tested today - no improvement. Only when I cleaned the WUR through its fittings with an air gun the problem went away.

Now it runs well; tomorrow I will give it another try. Perhaps I need to clean the WUR with compressed air and drive it a while so that the WUR will control the fuel distrubutor pressure, I mean the moving parts would be in motion for a bit longer time than just 15 minutes. I have had not time to drive this car due to other matters but now I will focus on this for a while. I have added one fuel system cleaner bottle also, I hope it would help get things working during a longer run.

Can the WUR jam underneath the membrane, because the fuel side should be clean now? Perhaps the compressed air moves the membrane but I use only 4 bar and the fuel control pressure should be higher...

Kari Pykäläinen

1971 300 SEL 6.3 #5581
1980 450 SEL 6.9 #7201
1987 560 SEC
1992 500 E
2000 G500

http://suomi.mercedes-benz-clubs.com/
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