Oh man, bad news on the 400E...help, techs!

[Pbalias]

Ok guys...here's the headache of the day:

The car is a 92 400E. After sitting at idle for an hour in the school parking lot today, she started running really rough. The temp was sitting in the 80-120 range (HOT for a mild day). Anyway...the fan wasn't on. I gave it some gas for about a minute to see if it would smooth out. As soon as I gave it gas, it smoothed out, and temp dropped to 80. I let the gas go, and the car sputtered and died. So I think, "Uh oh." I tried to start it again to no avail about 5 times. Then I put throttle half way down and tried again, it started. After it started, I let off the gas. RPM's jumped around from 0-2000 for about 5-6 seconds then it sputtered and died again. I gave it half throttle again and held it after it started, keeping RPM's around 2000-3000 for a good 30 seconds. Temp was around 80. It seemed to run ok but I could feel the slight roughness. I let off the gas, and within 30 seconds temp climbed between 80-120, RPM's jumped, she sputtered and died. All this time, I never heard the fan come on like it usually does around 80.

I own a Body Shop/Garage so after school I'm going to attempt to make it there. (It's close and I won't let it overheat.) I am going to trouble shoot with ALLDATA. But, I am still in the dark as to what to check. What can be causing this???? Now...I know I need wires, caps, and rotors because I checked them last week and they were corroded. I don't think this is the problem though because I don't think that would cause the car to get hot. Could it be a bad fan switch or thermostat causing it to get hot, and the computer shutting the car down? Or could it be electrical, like the alternator or battery freaking out the computer. The check engine light isn't on so I don't suspect any sensors. Basically...I don't know where to start...HELP!!!

Thanks a lot guys...lets see if we can't knock this out!

Peter

Peter,

I also have a 1992 400e. Last year, my wiring harness gave out and I had very similar problems.

First off, the wiring harness is a know weakness on the M119 engines. The insulation tends to get brittle and crack and wires start to short out. This harness controlls most of the engines electrical functions and sensors. The engine temp sensor is one of them.

The car was driveable, but it would buck and stall. So I was able to get home.

Check the harness first. It is located on the passenger side of the engine compartment in the rear corner. It goes from the main computer housing and contains the fuel injector connectors, throttle body connectors, distributor connectors, and the temp sensors up on the front of the engine.

You can just follow the harness to an area where the wires are exposed, or better yet, CAREFULLY cut into the rubber covering where it enters the engine bay, right by the valve cover on the rear of the engine. I will bet that the wire insulation is as brittle as glass.

Do a search on 'wiring harness' and you will see my original post. If this is the case, you may be able to get MBUSA to cover the cost, but I was not that lucky. The harness cost about $500. I installed it my self in about 15 minutes. The car ran fine afterwards. The only damage was to my temp sensor. It was shorted out, probably due to a spike.

Good luck. And please update with what you find.

-David

[Pbalias]

Dsantos...

Thanks for the lightning quick reply. Yes, I know about the wiring harness problem, and mine looks like hell. I checked it a while ago. I have a horrible feeling this is the problem. I really didnt feel like spending $500 on that stupid harness, as I am about to spend $500 tomorrow for caps, rotors, and plug wires. What really makes me sick is that the other day I was looking at a wiring harness that goes from the dashboard, out a rubber grommit and to the engine (on the left side of the engine facing the car) and the wires in it too are destroyed. (Hey...I read your post again and I think this is the same harness). This really bothers me knowing that MB used some $hit*y wire under the whole hood and it's all falling apart! I don't want to sound pessimistic, but I can forsee more problems with the electronics and engine management systems in the near future. :-(

*** I've already called MBUSA and they don't have the time of day, if you know what I mean.

Thanks Again...Peter

Peter,

FYI:

Pulled my invoice from the folder. The harness part number is 124-543-88-33. Price was $421.80. I don't remember if the dealer gave me a discount or not.

Good Luck!!

-David

[Pbalias]

thanks david, but i think my problem might be deeper than that...i'm still working on it though. it ran fine from school, but the damn thing is overheating. this i know for sure: the external fans are NOT kicking on. I'm currently working with my ALLDATA machine to find which (of the 4) coolant sensors control the fans. It is possible that the wires from the fan controlling sensor are shorting and not sending power to the appropriate relay. Problem is, my ALLDATA machine is not giving me what i want to know. I think I am going to post another thread for the techs...

again...thanks

PEter

[brianw]

Let me prefaace this by saying that 1. I am not a tech nor mechanically inclined, and 2. I feel your frustration, as I get hot under the collar when something on my car isn't 100%.

There was a TSB for this car when I recently purchased mine, and it covered this insulated (I think) relay that was responsible for sending power to the fans you refer. It is located on the drivers side near the front of the engine bay under the alarm system "horn". It is a little white piece and is susceptible to "frying" itself out.

When I purchased mine I had it replaced before this happened and when my mechanic removed it, it looked horrible. I'm not sure if it even worked, but had no overheating problem. But this was supposedly a culprit for overheating problems.

I hope this may help, and not merely cloud the diagnosing process.

Keep us posted on what you find, this is good info to have.

Dsantos, Thank you for posting the part number, I'll include in my folder of info for future use.

Take care,
Brian W.

[Benzmac]

The wire harnesses are being repaired under good faith by Mercedes in some cases with cars less than 120k miles.

That said, I have seen many throttle actuators cause those symptoms.

[brianw]

Benzmac,

Could you shed a little more light on the definition of "some cases"? I have less than 120K and am wondering in what instances they are willing to help with costs. You never know when this may happen to you.

Thank you,
Brian W.

Not to pry but why were you in a school parking lot idling for an HOUR?

[Pbalias]

i get there early to beat traffic and wait 1 hour for class to start. Rather be sitting in a parking lot than on the SW Freeway in Houston in Morning Rush-HOur!

[geoellis]

Do you tend to idle this car a lot? I'm sure the harness is poorly made but idling any car for an extended period of time is a really bad idea for a number of reasons. The heat build up alone under the hood is enough to trash the wiring. In fact, car manufacturers don't even recommend "warming up" a car on a cold winter morning beyond a minute or two. Turn it off, it's better for the smog problem in Houston.

Sorry to be an old lecturing coot, but don't EVER idle an engine for an hour, don't even idle it for five minutes. It's not good for it and wastes gas. It builds carbon and will make it run like a dog.

I guess you've learned your lesson now.

Best of luck,