E300 Turbo Diesel problem

[comfort zone]

I have a 1997 E300 TD auto with electronic Bosch fuel delivery pump.
The car runs very well before it completely warms up to normal running temperature, about 80c. At that temperature it accelerates and pulls well, the problem manifests when taking your foot off the throtle and slowing down. The engine appears to misfire and there is a noticeable "wobble" from the engine as the revs drop. When arriving at normal tick over speed the engine again runs smoothly.

With the car stationary you can, when it is at normal running temperature, rev the engine and see and hear this "misfire". Untill the engine is at normal running temperature this does not occur.

The fuel pump has been removed and examined, re calibrated, adjusted by a reputable diesel engineers and this makes no difference. Bosch technical department have been consulted and they can offer no help. The ECU has been replaced and checked. The vehicle shows no faults on diagnostic test equipment! The gearbox and torque converter oil has been changed and so has the gearbox electrical connector housing, there are no faults! There are no leaks in the fuel system, but the problem persists.

It has cost a lot of money so far and I am no nearer now to finding the fault than I was 2 months ago. If there is anyone out there who has any practicle suggestions I would be pleased to hear from them, so would the diesel engineer!
Thanks, John

 

[Uncle Benz]

Have the injectors been checked?

 

[Parrot of Doom]

AFAIK when you back off the throttle and engine brake, the fuel supply should pretty much cut off to the engine. You can feel it happen when using the gearbox in manual mode - personally I hate it, its like an on-off switch.

Anyhow, perhaps that system isn't working as it should, and some cylinders are getting more fuel than others?

Total guess, so feel free to shoot me down in flames

 

[comfort zone]

Have the injectors been checked?

Yes, set of recon injectors fitted in May.

 

[comfort zone]

AFAIK when you back off the throttle and engine brake, the fuel supply should pretty much cut off to the engine. You can feel it happen when using the gearbox in manual mode - personally I hate it, its like an on-off switch.

Anyhow, perhaps that system isn't working as it should, and some cylinders are getting more fuel than others?

Total guess, so feel free to shoot me down in flames

Thanks for the guess, but that has been checked too. All cylinders are getting the same quantity of fuel!

Keep then coming!!!

 

[Bolide]

What Uncle Benz said - injectors? Maybe one's dribbling

You say the fuel pump has been checked - do you mean the fuel pump in the tank or the injection pump?

Have you gone over the engine with a stethoscope?

It makes no sense that there's a "misfire" on the overrun. The fuel feed is off (I imagine) when the throttle is closed and there's no "fire" to "miss". I don't think it's combustion-based. As you've gone over the fuel & electronic systems I'd look at mechanical things

Is the EGR working properly? Does the TD engine have the butterfly valves in the variable-length inlet manifold that the 606 NA engine has? Are they working properly or is one oscillating? Does the "misfire/wobble" occur at specific revs?

Does the car have a dual-mass flywheel or a crankshaft damper? Is there a bad bearing in the belt path at the front of the engine? Are the engine & gearbox mounts OK?

Is the misfire/wobble/vibration enough to shake the engine on its mounts? Is it like one cylinder missing or is it a surging of the revs?

Have you looked at how the warm-up regulator interacts with the fuel feed & injection pump? Is this system affedting the car when it's warm?

How many miles has the car done?

Just a few ideas!

Nick Froome
www.w124.co.uk

 

[Parrot of Doom]

http://mercedesshop.com/shopforum/showpost.php?p=1153172&postcount=1

Try that. Courtesy of a nice chappie on http://www.mercedesshop.com/shopforum/index.php

 

[comfort zone]

What Uncle Benz said - injectors? Maybe one's dribbling

You say the fuel pump has been checked - do you mean the fuel pump in the tank or the injection pump?

Have you gone over the engine with a stethoscope?

It makes no sense that there's a "misfire" on the overrun. The fuel feed is off (I imagine) when the throttle is closed and there's no "fire" to "miss". I don't think it's combustion-based. As you've gone over the fuel & electronic systems I'd look at mechanical things

Is the EGR working properly? Does the TD engine have the butterfly valves in the variable-length inlet manifold that the 606 NA engine has? Are they working properly or is one oscillating? Does the "misfire/wobble" occur at specific revs?

Does the car have a dual-mass flywheel or a crankshaft damper? Is there a bad bearing in the belt path at the front of the engine? Are the engine & gearbox mounts OK?

Is the misfire/wobble/vibration enough to shake the engine on its mounts? Is it like one cylinder missing or is it a surging of the revs?

Have you looked at how the warm-up regulator interacts with the fuel feed & injection pump? Is this system affedting the car when it's warm?

How many miles has the car done?

Just a few ideas!

Nick Froome
www.w124.co.uk

Some good questions that I don't know the answer to, but the diesel engineer will I'm sure as he has spent many hours watching listening and working on the engine and removing the injection pump several times!
The car has done 152,000 miles.

 

[comfort zone]

http://mercedesshop.com/shopforum/showpost.php?p=1153172&postcount=1

Try that. Courtesy of a nice chappie on http://www.mercedesshop.com/shopforum/index.php

Excellent PoD! I will tell my engineer, it will give him plenty to think about!

 

[comfort zone]

I have made many more enqs about this problem, and posted more on the website refered to by "Parrott of Doom".
This is the link http://www.mercedesshop.com/shopforum/showthread.php?t=169781

Below is may most recent posting and maybe someone on here has some answers!

Since I last posted I have consulted my diesel engineer and Merc main dealer.
My diesel man liked the ECU article by Stu Ritter, as he now believes that there is a softwear glitch.

I took the article along and showed the Merc dealer and was surprised that he didn't freeze!
He made enqs and told me that the part no quoted for the ECU was not a part number they knew and was probably a US part number, not British.

I have done other enqs and was lead to believe that any part no that ended 05, was the subject of a recall. He checked recalls and there was not one for this part, neither had my car missed any recalls.

He said I could have a chassis matched exchange ECU! I really can't see how that would be any different to the one I have!. But suggested my car go on their diagnostic tester first. I may well just do that so that when it shows no fault I can say "what the hell is that then?"

I am going to run the car with headlights/aircon just to test Steves theory.

Is there anyone who can confirm that part numbers are different for USA and GB and that 05 denotes a recall, and confirm the part number given by Stu Ritter are correct, and even where I could lay my hands on one of those ECUs?

Thanks again, John.