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C36 flat spot/hesitation is SOLVED!

6K views 7 replies 5 participants last post by  bongC36 
#1 ·
For the last 5 years my 95 C36 had been suffering from a flat spot between 3200 and 3600 RPM. Acceleration is very brisk until it reaches 3200 RPM then it slows down considerably, picking up again only after 3600 RPM had been breached. I inspected and replaced the usual suspects: MAF, plugs, coils, coil-ends, etc all to no avail... I had already replaced the infamous wiring harness ($$$) so I gave up and just lived with it.

About 2 months ago, the problem got worse, with the car randomly refusing to go above 1500 RPM. Exactly 1500 RPM the fuel will be cut off and resume only at 1000, then cutoff at 1500 again...ad infinitum, jerking and bucking like a nervous rabbit.

I chanced upon an old post that the short wire leading to the Electronic Throttle Actuator (ETA) might be defective so I slit open the rubber cover and inspected the wires within. Aha! the insulation of the small wires inside had turned to dust and the BARE wires are rubbing against each other

Since this is a very expensive part, I just replaced the wires individually and soldered it back together and was pleasantly surprised to find that not only is the 1500 RPM limit gone, the flat spot is gone as well! Now the C36 performs again like when it was new, no more pause (to think?) at 3200 rpm but just zooms to redline before shifting! oh joy

So if some of you guys are experiencing some weird electrical gremlins and it is not cured by the usual suspects and by replacing the wiring harness, then consider checking the cable to the ETA, it just might be as bad as the one I had.

Here is a pic of the condition of the wires that I found!
 

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#3 ·
good job. I know either here or on mbworld is a fully illustrated DIY guide on rewiring the whole throttle actuator. I'm planning on doing both sometime soon. Randy P said he has wiring diagrams hopefully they will help. What gauge wires are in those harnesses?
 
#5 ·
Bong my AMG has this hesitation only after it has warmed up considerably as in after I drive it briskly on hot days. More so after I turn it of and it heat soaks for some time then start it up and drive again. Then the flat spot is very pronounced and on very hot day after serious hard drives I feel it hS a smaller flat spot over 5000rpm.

Is that how ur car was? And now that u have driven it after the fix for some time have u noticed any sign that the flat spot has returned? Or is it completely gone?
 
#6 · (Edited)
well i just did this my self and its amazing how bad the harness was!!! i was blowan away and have no idea how it was running.. any way no more hesitation:) thnx bong

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#7 ·
update, the car drives way much crisper now and the throttle response is noticably better. but i still have a tiny hickup in the power band at exactly 3450 rpm. i mean its just a point where power dips and resumes right after.can it be the resonance flap switchover!!

bong give us ur feedback man.
 
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