hesitation problem solved 92 400E
 

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.

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

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.

Fantastic Info on R & R of Intake
 

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

Problem fixed this time - so far
 

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

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

Please post part number for the FPR
 

Thanks:D

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.

Re: Problem fixed this time - so far
 

Rafi,
Do you recall step by step how did you replace the FPR? Do you have to cut off fuel line somehow so you don't get fuel all over the place? How did you manage? any level of details will be great help for me. Thanks.

relieve the pressure
 

by removing the cap at the front of the fuel rail nest the T-stat housing and bleed the pressure off like letting the air out of a tire. This will allow the the FPR to both come out easier(becuasae there will little to no pressure applied against it and lessen the amount of gasoline that spills out. Word of caution, have the replacement in hand or vcertainly at the ready so that you can plug it in IMMEDIATELY after removing the other. At almost $2/gal , you certainly don't want 93= octane spilling all over the concrete

Joseph_H It is very simple there may by be some gasoline that seeps about not much in my case place the new part in.

Stepwise:
1. remove the filter housing to reach the FPR
2. remove the vacuum hose to the FPR
3. remove the snap ring on the FPR
4. add a dab of oil to the new FPR 2 O-rings
5. remove old FPR
6. install new FPR push down in rioght angle to FPR holder while wiglling the FPR by holding the vacuum hose connector.
7. install the snap ring
8. connect the vacuum hose to FPR
9. dry the area around FPR
10. turn on the ignition key to see if there are any leaks.
11. install the air filter housing and its accessories.

Thanks Rafi
 

Great step-by-step details. I am in process of troubleshooting an issue where my 95 E420 engine shakes when i first start the car after being parked for 2-3 days. in my case the shaking stops once the engine is warmed up and this problem doesn't happen that often either. This happened twice so far after the car is parked a lengthy time. Just wondering if the FPR, among other things, can be the culprit. :confused:

Re: relieve the pressure
 

aldedmon,
You lost me there.. I think you meant next to the T-Stat housing while reading your post sound like I need to remove the t-stat housing. On my M119 engine, there is what looks like a release valve with a cap setting on the fuel rail almost to the right (standing in front of the engine) it is under the front engine cover and kind of above and behind the power steering reservoir. So i remove the cap and press something to let the air out? Would that also release fuel as well? Please explain. Thanks.

hello everyone !!! i"m a machanic work out at home , i do alots of work on late model BMW & MERCEDES , so far i fix two sl 300;500 with exact same problems as you guys posted here after these cars went in and out of other shop end up with a longs list of replacement parts i mean all of ignt & fuel except it fuel injector, finally come to me , here what i found the cars would start & run fine when it cold but when it getting warm up it start to run rought like miss fire , will not moved like it should when speed 5 to 15 MPH @ 1k to 2k RPM unless you give it alots of gas at the padal then for a split second delay it woke up and jump , for hight speed no problem , another things after it run hot you shut it down for 5 min or so , will take a fews crank to start up and smell like raw gas . btw forgot to mention both of these cars got there fuel injectors clean by injectors shop with professonal machine . if all of the above sound like your problems , replace all injectors and seal , the cause is these injector or injectors only leak down when hot (matal on injectors check valve expanted due to heat) make your engine run idle with too much gas (rich) ,after hot shut down it leak down to your intake cause hard to start . hoped this will help some of you guys before spend too much money.

Luan, Welcome aboard!
 

Do you have experience with cars that have idle problem when cold? My car does this once in a while after leaving it parked in the garage for 2-3 days once I start the engine she shakes for few minutes at idle then drives fine and doesn't do it again. I had this happen twice already in the past few weeks. Any ideas? Thanks.

JOSEPH next time leave your car park for a fews day , before you try to start the car charge the battery up ,weak battery(loose juice after sitting for awhile) will cause car run rough at idle until altenator charge it up full ,OVP relay will cause hard to start or no start at all ; cooland temp sensor for the ECM or ECU which ever you call it's some time fail and computer don't know the engine is cold to provide richer fuel mixture when cold start . hoped this help , luan
:)

Thanks for the ideas..
 

I heard that coolant temp sensor could be a culprit in this case and I will test it and replace it. I replaced all spark plugs today and replaced various vacuum hoses with new ones just to make sure these were not an issue. I haven't checked my battery in a while. It is in the trunk. I will take a look and see if it needs distilled water or something. By the way, is the coolant temp sensor the one that has 4-pins? There are three temp sensors setting next to each other on the front side of the engine. One has 1-pin, the other has two (blue connector) while the third is round with 4-pins. Thanks.

cold start
 

hello JOSEPH , the sensor with 4 pins is the one , but i still think is your battery is weak cause , if it was your temp sensor , it would act up on you every times you start it cold , battery could become weak even water level still full !!!