400E strange hesitation/acceleration problem PLEASE HELP

[amg280]

Hello all. After do much searching, I was unable to locate anything on my problem. So I will give it a shot here.

The car is a 92 400E. What it is doing is on heavy acceleration (mostly WOT), the car will start jumping, like someone is turning the ignition key on-off-on-off-on-off (vroomm..pause.....vrooomm.....pause...)very cyclical in nature. If I keep on the gas, it will eventually go away after a few seconds and start acceleration very powerfully and linear like it should.

I have tried my best to narrow down the problem and this is what I have found. The car hardly ever does it in second gear. Always in 3rd, and in 4th too at high high speeds. It always seems to occur over 4000 RPM. If I hold it in 3rd gear, at about 100, then give it gas, it will do it religiously. If I ease off the throttle then get back on it smoothly, it wont do it. Problem is always present at 100+MPH. And I might note that when it does this, the car barely accelerates.

One thing of note also, is that I think I have been noticing during hard acceleration, and I hit a bump in the road, it will send it into this weird "mode" momentarily.

Some people have suggested that I replace my Mass Air Meter. But I dont think this would cause this. Would it? I know that my wiring harness isnt in the best shape. But I dont want to go throwing parts (read: $$$$$$) at this without a method of narrowing down what it could be.

One thing I brainstormed up is could it possibly be one of the sensors on that tranny that retards the ignition during WOT shifts? Im out of ideas guys. Please advice.

-Andy

[carman850]

My 400E had very similar problem before, at highway speed, if I kicked down for max accerleration, the rpm wouldn't past 5000 rpm, as soon as rpm reached 5000 rpm, the rpm went into a kind of violent oscillation. ABS and cruiser control also didn't work.

I found out one of 4 10A fuses in the black computer box was shot, after checking the schematic, I found that fuse protected throttle control module and ABS module.

A 50 cents new fuse sloved these 3 problems, the computer box locates at the passenger side just behind the firewall.

[amg280]

carman850,

I appreciate the response. Unfortunetely, I already check all of them. I was hoping one of them would be broken. Anyways, I might play with it a little more tom. When the ASR is in limp home mode, does anyone know the % of throttle is allows the engine to get? Cause when its in limp home mode, the electronics (I think) and shut down, and u are manually moving the throttle via the cable like a normal car. I might put it into limp home and see if it still does it. Just another thought.


-Andy

[amg280]

Ok,

I just tested it and it DOES do it in limp home mode too. So I guess I can rule out the fluctuation is not due to the throttle butterfly moving, correct?

-Andy

[amg280]

Ok. I think I narrowed it down!! I took apart part of my console, so I could access the main harness plus for the transmission. I unplugged the transmission plug (behind the radio) and the car DOESNT DO IT ANYMORE . Not only does it not do that hesitation thing anymore, but the car goes like HELL!!!!! It feels like its 500 pounds lighter. Right when it hits 3500, its like a turbo kicks in. Very strange. Ofcourse I have no speedo, reverse lights, etc etc. Maybe I should just leave it unplugged and get a GPS to monitor speed.

My question is, what output out of the tranny is most likely causing this? There also could be a short in one of the wires going thru the gromet, since I did notice that hitting bumps aggravates this.

Someone with an knowledge of this tranny please shed some light on the subject. What are the certain sensors on it for? I know it has a ton more than my old 420SEL.

Thanks,

-Andy

[amg280]

I forgot to mention that for some reason, ASR still functions normally with no speedo.

Do you have a full size pic of the one in your avatar?

[amg280]

Do you have a full size pic of the one in your avatar?

Maybe, as long as your not a trooper

[tom woolner]

Check in the archives for 500E. I remember that some one was struggling with a limp home problem that originated in the transmission. Other than that, I can't remember the solution.
Tom
92 500E

[danield]

I had a similar problem in my 260E. I recommend checking your transmission fluid level. My fluid level was low.

It's a long shot, but it might be the issue...

[amg280]

Well, I cleared out all of my codes in the computer today, then drove it 30 miles. Then rechecked them. The computers spit out 4 codes:

code 8 (Ignition module): Tranny overload switch does not close

code 5(ASR): Stop Lamp switch (S9/1)

code 6(ASR): Starter lock-out/backup lamp switch (S16/3)

code 14(ASR): Closed throttle position contact switch (S29/3)



Could any of these things make the car behave like it is? The tranny switch seems like something I should target. hmm..


Anyone anyone???

[mcelroyb]

I recently replaced my trans due to failure and have the same rough idle and acceleration as AMG. Prior to the new trans my car accelerated and ran smoothly. Since the new trans, my cars feels like a junker upon start. This problem usually goes away after 30 minutes of highway driving. I returned the car to the dealer and their diagnosis was engine mounts. Can this really be the source of my problem(s)?


AMG....

Since I am from Syracuse maybe I'll stop by and compare notes the next time I am in town. Whatever you do, don't take your car to Romano Motors. They claim to be experts but provided me with novice like service......

Brian

[amg280]

Brian,

Next time your in Syrause, drop me a line.

As far as Romano Motors, yes, I have had TERRIBLE experiences with them. I had my car there last August with this problem, and they never fixed it. I can honestly say that I know about 10 times as much info about mercedes than the service managers do there. I would constantly prove to them how they are wrong. They didnt like this.

I ordered a new transmission overload sensor and pray that it is going to solve my problem. I have cleared out the codes 3 seperate times, and this one constantly comes back, the last time, all by itself. Say a prayer.

Your rough idle could be the engine mounts, although, if its really rough, could be a combination of things.

-Andy

[mcelroyb]

Andy,

Please let me know if the sensor fixes your problem. I am curious as to what may solve mine.

Where did you get the 2.82 diff?

Brian

[amg280]

I FIXED IT!!! YAHHHHHHHHHHHHHHHHH!!!


I put the new sensor in it today, and presto, the car runs like a dream.

I had to drop the pan to get the appropriate leverage to the sensor, and then had to run all around town to search for an O-ring, good thing my hardware store had metric ones.

I also notice that my WOT shifts are like glass. Im so happy its fixed.

-Andy