1994 C280 - Limp Home Mode??
 

Ok, we just got this car. I've done a search but not sure I've found an answer. It has a brand new-remanufactured engine in it. I've had it back to the shop once on this problem, but it's still there: If you accelerate HARD at highway speeds, the trans downshifts, and when it hits 4K RPM (I haven't done a lot of this, as the engine's still in break-in mode), it starts to stumble and won't accelerate. Then at idle, it shakes like mad. The only way to get things back to normal is to shut it down and restart. Then, everything's fine. It sounds kind of like the limp-home mode on the 500...

Thanks in advance.

I wonder if it has anything to do with the variable valve timing mechanism.

Do you know if the engine wiring harness has been replaced?

Are you running the standard copper core non-resistor plugs?

Have you changed the resistor boots on the three coil wires?

See if it cuts at 4K in N/P ....

Arthur, the rev limiter DOES kick in at 4K in P/N - normally. Just "bumps" 4K, and comes down. No remaining or residual effect on how it runs. This is what Randy, my mechanic (and the guy who I bought the car from), thought it would be. This problem requires a shut down to "reset". In reading about "limp home" in the archives, it sounds EXACTLY like that. Loss of about 70% of power, idles rough, etc. Seems to happen when you kick down the transmission??? Somewhere else in the archives I saw a note about a Transmission valve or something? Any other thoughts??

I believe that the wiring harness HAS been inspected - but I'll make sure. Running normal old copper plugs. Wires, boots, etc. were replaced when engine was replaced. Fortunately, it's not my $$ problem (it's Randy's), but if someone has some ideas that would save him some digging around AND me some shop time not having the car, it would be appreciated! As usually thanks for the responses!

If the harness is the original, it doesn't matter if it's been inspected.

It's either bad or on its way to being bad.

The insulation of the wires is defective.

The tranny does have an Overload Pressure Switch that will cut the timing above 1.8 bar.
This can happen under full load downshift [ your complaint]
The sw is OPEN at pressures less than < 1.8, so Randy may want to disconnect it for testing only.. [

On the 4K rev limit in N , that is torque converter protection ..
This is supposed to be speed sensed over-ridden when you move > than 5 mph..
A test for this circuit is to get the car moving [ I use 20mph]
and manually shift to N . Then test the RPMS ... the 4K feature should be eliminated under these conditions...
Randy prob knows this anyway, but ...
See what that gets you

It sounds to me like the engine ECU is cutting the fuel supply to one or more cylinders. The computer will cut fuel to individual cylinders IF a misfire is detected. Fuel management does this to prevent raw fuel from running through the catalytic converter. Sounds to me like you've got a spark problem.

You say the engine was replaced... so I can't imagine them to not change plugs/wires/boots.

A poor spark in the cylinder is probably causing the misfire. Check spark plug condition, plug wiring, plug boots/coils, and the connections between them.
Also, it's important that your car has OEM plug wiring, Bosche COPPER spark plugs, and secure connections at the boot.

Also, low-grade & low octane fuels can make it worse.
If a cylinder is not getting good spark, that cylinder may misfire if the engine is revved higher... more likely to misfire the higher the engine speed.

This happened to me @ 110,000 miles on my 95 C280... The problem got progressively worse... the problem? Worn plug wiring...
I replaced the plug wiring, the 3 coil boots, and the 6 spark plugs and the problem was cleared.


Good luck

It definitely sounds like mis-fire detection, though the check engine light should have come on instantly. I would check the mass air flow sensor. If your mechanic has the means to read the air flow quantity while driving the car it's easy to check. Most of the time there's no problem until hard acceleration, then it feels like your towing a bus! Also, find out if the same cylinder(s) are cutting out. That will help narrow it down. Good luck

Arthur, it accelerates fine in neutral over 4000 rpms at ~20mph. I'll have Randy check out the other items. Thanks, folks.

A misfire won't always light the check engine light; however, it'll store a code telling what cylinder is mifiring.

A mis-fire that results in a cylinder shut-off WILL light the check engine light as soon as the the shut-off occurs. An intermittent mis-fire that is not calculated to be damaging to the cayalytic converter is simply stored as a DTC. If the same event should occur on two consecutive "trips" the CE light is turned on at the beginning of the next trip. When reading codes the difference is simply an "A" code or a "B" code. The "B" code is the one that results in cylinder shut-off, if it occurs at a frequent enough interval. Cycling the key will begin the next "trip". The cylinder that was previously shut off will operate normally until the fault re-occurs. Once a cylinder is shut off(via fuel injector interuption) it will not come back on until the key is cycled. I hope this clears things up.

Well tell my Mercedes ECU that... I have a totally cylinder shut-off right now, with stored fault codes, but not a Check Engine light.

I asked my dealer the same thing...

According to OBDII information from several years ago, a mis-fire that is deemed to be non- cat damaging will result in a flashing CE light. I've driven ME-SFI equipped vehicles under actual fault conditions and the light came on as soon as the fault occorred. These faults however, were of the cat-damaging type. I can tell you that there are differences in the "fault-set" criteria as well as MIL activation when comparing the different MB engine management systems(LH, HFM, ME) as well as different engines. If you have a cylinder that has been shut-down and codes are being set, I can't imagine why in the world the CE light isn't coming on. You said that you asked your dealer the same thing. What was their reply?

You know, it was a long time ago, and I forgot what he said... in any event, I remember it making sense.

I dropped my car off @ the dealership today because I must've been running on 3 cylinders. I didn't think about it today, but when I pick it up tomorrow, I'll ask again... and tell the problem.

Also, check engine bulb was replaced about a year ago, so that's not an issue.

BTW, this information pertains to my 1995 C280 with 137k miles on it.

1995 C280 (& S320, SL320, E320) were all fully OBDII compliant. Yes, one year early. It's fully certified.
Here is a picture of the emissions info under the hood... it's the hardest thing to read, but there is an arrow towards the words "OBDII Certified"

Have a good day.

David, if you can get a copy of the codes found, as well as the repairs performed it may help shed some light on the subject. Thanks