Weekend Arm Chair Diagnosis needed.(The dreaded harness!)
 

... just to ease my nerves, help me out here with this one.

1995 e320 W124 automatic trans wagon. Running down the road with Wife behind the wheel.... all the sudden, she says it sort of hesitates (she has trouble describing this but it sort of acted like it didn't want to go or it sort of got hard to go forward or similar to lost power but no change in engine rpm) for just a spit second it does and she says then started shaking. Shaking so you can feel it through the whole car. No CEL light, No hesitation and no change in rpm and no change in response to application of fuel. Running and shifting normal except for this vibration. Increases when put into drive but shakes so you can just feel it when in at idle and out of gear. Can see the motor vibrating side to side.

I am first guessing a motor mount or the transmission mount went. Ruling out flex discs because it does it at idle sitting still in park. And I am ruling out issues with transmission or motor because it runs well and the idle RPM is steady and clean and it responds to throttle application well and it shifts fine.

The only mystery is her description of momentary hesitation before the shaking started.

Also of concern it I may have jinxed myself by ordering new Wheels and Tires from Tire Rack for this thing, at the tune of just over $1000 on Friday!

TIA

fuel pump relay trying to go bad or ovp relay trying to fail.

Interesting... would cause vibration without motor RPM changes?

New symptoms based upon road test to take it to the Indy...

Does indeed not want to go fast or match speed to throttle. Floored its doing like 50 mph. Shifts but shifts hard. Jerks more than normal. Vibration smooths out when at top speed but always persistent.

Vibration less but still there at idle in park or neutral.

Engine smooth and seems normal and responsive and no miss or stutter.

Makes me go back to thinking Transmission now... 156K on the thing but well serviced transmission that has not missed one lick and always shifted nice a firm and correctly. But who knows. More thinking something in the control of transmission perhaps?

Then look carefully for vacuum leaks, especially on the line between the transmission and the intake. -CTH

95 e320 can we assume that the wiring harness has been replaced and the electronic accelerator rebuilt?

We have to assume the Wiring harness was redone because the one on it is mint and newish in condition. It has been inspected for that (in fact before I purchased it and since then as well). It was not done by me though. But the one in it has no identifying tag of any kind to be 100% confirmed however the ends of all inspected plugs and places in between have nice pliable insulation with no sign of deterioration. And my very detailed book of service records I inherited with the car stops around 100K when it was transferred from owner number one to number two. Then I am owner 3. But... It appears that both the Head Gasket and wiring harness were probably done somewhere in that previous time period though.

The Throttle Position Module (whatever the correct term for that is) was replaced just recently. Is that what you mean by Electronic Acellorator module? This is the very expensive one even to rebuild? The one that is rebuilt in some place in NC? if so then yes. That one still hurts! and that is still under warranty. That was done a few months back.

A few other relays done here and there. A couple of new Coils and the insulators for those also done recently. Was now and still is running like a top engine wise.

A minor vacuum leak fixed one time recently but nothing major in that regard so that is a suspect area...

Well spank my ass and call me Judy...

fix so far was a new Coil Pack... the one of the three we had not changed out yet.

Go figure... does sort of go along with other's theories of loss of power though. But hard to wrap your head around with these sorts of symptoms.

yo judy alls well that ends well.

I just read your descriptions, and I was going to say that one of your cylinders is out, for whatever reason. That's why the engine smooths out at high RPM.

Motor & tranny mounts wouldn't cause vibrations like that, either....

But, what's strange is that the CEL light didn't come on. Misfire should cause the light to go on.

Check that when you turn the ignition to ON (not start), that the CEL light bulb is working....

I believe that it takes more than one misfire event to turn on the CEL, not sure though. Memory tells me that there are some 3-event CEL triggers.

My symptoms were very similar, but I was getting a code 5 on the DM and code 13 on pin 8. All mine ended up being was the spark plugs. $12 at NAPA. Crazy *****, ain't it Judy?

Best Regards,
Rob

When I had the coil pack for cylinder 2 die in my W124/M104, my CEL didn't light up either.

That's strange. You'd think it's be set up so a cylinder not firing would cause the check engine light to go on....

I guess the difference with mine is the model year. Mine's a '97, and when one cylinder's coil or fuel injector is out, CEL goes off. Also, the OBDII tells me pending codes....

My issue has resurfaced after a week of smooth sailing. Not as pronounced but returned none the less. However I can get it up to speed and eliminate it if I try but its at lower speeds and at idle I get the shakes again. Started yesterday after a 30 minute highway run as I came off and came to a stop light.

Going to read the codes on this one and see but I am more and more suspecting a bad OVP now.


I guess the CEL is not likely to come on in these cars because the cutting back on the power does not create an emissions issue. Nothing is emitted from a cylinder that is shut off by the system as it gets no fuel to do so.Mine did indeed set the light a few times when the first Coil went out. It was just skipping and missing when that occurred. Not shaking and losing power.