Thanks to this site I was able to fix my hesitation problem.
I have a 92 400E (M119) 165K Mi. The car would be fine when cold but when it warmes up it would miss at idle specially with A/C on. It would also miss or hesitate when starting to move from stoped position or if tried to accelerate quickely. I changed the distributor caps, rotors, Spark plugs, spark plug wires, checked for vacuum leaks, they made no difference. I did all that repairs over a period of ~ 10K miles. I finally took out the fuel injectores and washed them in the ultrasonic bath with gasoline and isopropanol and after I put the injectors back and started the car it was smooth as it ever been. Before I took out the injectors I used injector cleaner in the tank but that did not do anything.

I forgot to mention that I also did replace the engine wiring harness due to insulation breakdown (well described on this site)but that did not solve my hesitation problem at the time.

The hesitation problem started to come back slowly and now it is as bad as before. I guess while the car sat for few days something happened that eliminated the hesitaion problem.
Two tracks I am thinking on working on. Ignition coil possibility or the throtle actuator which is expensive and very hard to get to.

Interesting... you are describing the problem I have with my 92 500SL.

Mine also improves after 'resting' and gradually gets worse as I drive it regulrly. I do think it to be the injectors because they are about the only things that haven't been replaced.


I have a 92 400E that runs fine. The injecton systems on these cars are VERY different.

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

Sounds fuel related

Have you pulled the outlet fitting from the gas tank and cleaned the screen (is there one)? Improvement with resting sounds like debris floating away from the screen, then re-accumulating after the engine has been running.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Rafi - how difficult/time consuming was it to pull your injectors?

speace:
have you changed/tested your ignition coils? or the "gas actuator slide" PN 000 141 79 25 if w/ASR and 000 141 78 25 w/o ASR ? this sits on the lower part of intake manifold, below air mass sensor? what about the air mass sensor?

sbourg:
I know there is a screen (PN 119 078 00 56) in the fuel distributer rail, I did not change it unfortunately. Mabe next time I take out the injectors.

tkd_M119:
The injectors are easy to get to and change depending on if your wiring harness is new and the vacume hoses are new or if you can get them off without breaking or crumpling in your hand. Putting it back together is more difficult since you have to line up all injectors at the same time so that the rail can fit on all of them at the same time. I think it would be better to mount the injectors on the rail first then placing the injection port end to the intake manifold all at the same time later.
I do not recommmend DIY since you have a lot of fuel and the chance of not reinstalling properly in the rail. If I knew what I was getting myself into I would not have done it myself.

Check out this link:

http://www.pindelski.com/cars/W126/W107_intake_manifold/W107_intake_manifold.html

I kept this from a post several months ago. It is an incredibly comprehensive collection of info (including tons of photos) that walk you through disassembly/assembly of the complet intake side of an MB engine. Very enlightening.

While it is for a V-8, the info is very easily adapted even to my 2.3 ltr in-line 4. With the help of this info, I will be completing the entire process in the near future on my 201.


Jeff Pierce

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Jeff Pierce

Current Vehicles:
'92 Mercedes 190E/2.3 (247K miles/my daily driver)
'93 Volvo 940 Turbo Wagon (263K miles/a family truckster with spunk)
'99 Kawasaki Concours
Gravely 8120
Previous Vehicles:
'85 Jeep CJ-7 w/ Fisher plow (226K miles)'93 Volvo 940 Turbo Wagon
'53 Willys-Overland Pickup
'85 Honda 750F Interceptor
'93 Nissan Quest
'89 Toyota Camry Wagon
'89 Dodge Raider
'81 Honda CB 750F Super Sport
'88 Toyota Celica
'95 Toyota Tacoma
'74 Honda CB 550F

The latest repair I did was to change the fuel pressure regulator that sits on the fuel rail, near the firewal, you will see it after you remove the air-filter housing. It has been a week and so far the problem seems to be gone. If it reapears, I will let you know since there a many people reading the post even though not many are posting themselves.

Rafi, if the problem returns, the screen I am referring to would be at the gas tank, before the fuel pump/filter/accumulator. Usually inside the tank outlet fitting.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

sbourg - I understand that the propblem appears to be fuel related. It is also temperature related - from the symptoms. Does the filter/screen at the fuel tank see temperature change as the the engine temperature goes up to operating temperature?

Rafi & Steve,
Would a bad fuel pressure regulator distort the duty cycle readings?Thanks.
Rich

Thanks

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Regards,

Albert
aldedmon@yahoo.com

aldedemon - my FPR part number is 000 078 18 89.
richard28 - I am not familiar with duty cycle reading, need to define what you mean ( I am only amature mechanic on weekends). From what I read FPR keeps the LH injectors running at 38 psi fuel pressure and when there is vaccum from the intake maifold, due to opening of throttle plate there would be vacuum and that would increase the FPR pressure to 45 psi to increase fuel delivery (FPR has a vaccum connection to the maifold). All these are too fast for (lambda) Oxygen sensor to monitor and micromange the operation of the LH inection. I would guess in my case that the FPR when it got hot from the normal engine operating temperature was not maintaining 38 psi or increasing to 45 when there was demand and that is why it was missing and hesitating. It makes sense, I was getting very good gas milage when it was missing due to fuel starvation.