BongC36

My 95 C36 sometimes loses power under hard acceleration and when under heavy load like charging uphill. With the throttle maxed, The RPM will shoot to around 3200, sort of hesitate for a second or so, then there will be a burst of power and the tach will climb rapidly again, then repeat. It's driving me crazy.

So far I've replaced the following:
Wiring harness
MAF Assembly
Coil packs and connectors,
Spark plugs/AIR/OIL filters
Oxygen sensor

What is exasperating is that this behavior only happens intermittently, there is no pattern nor common trigger that will help isolate the problem. I've had the car since it was almost new (17,000 kms) and regularly hits 255 kph with it, so no major problems with the motor.

Has anybody experienced this peculiar problem? Cure?

C43AMG

When was the fuel filter last replaced?You've replaced everything to insure proper combustion , but it seems you've overlooked the fuel delivery.

jayrasheed

i have the same darn issue on my 95 36
its at abt 3500 every time and then full power by 4000
now i think its the over load switch in the gearbox. Its more of flat spot on my car.
I see thats the one thing we both have not checked and on my new w140 500 i have a similar issue
but more sharp i was told its this switch that does it.
So if ur set to fix it try that.
I still hadnt had the time to go fix it my self so i cant confirm to u for sure.

BongC36

The fuel filter was last changed about 6 months ago, along with the plugs and filters. Jay, you have exactly the same symptoms too? Does you 36 stop accelerating hard at around 3200-3400 then suddenly spurt quickly past that? Any idea where is this overload switch?

jayrasheed

yup i have that same issue
the switch is on the left side of the gearbox has an electrical plug on it but i am not so sure u if the oil pan needs to be out for it to be changed.

Last i heard the part is abt 180 usd alone and then add labor.
If oil pan needs to be out change the oil and filter while ur at it. Gearbox oil that is.

ob1kenobi

From your list above it doesn't look like you've replaced the CPS yet.

It could be the source of your problem.

good luck.

AMS Performance

Could be cam position sensor as well (different from crank position sensor). 3200-3500 is where the cam starts to open up so that could explain it.

Also, all the M104s tend to have that flat spot in that area but on the C36s its more pronounced. The only thing that really helped when I had the C36 was going to a lighter crank pulley. It didn't make it disappear completely but you couldn't feel the power loss anymore it just quickly accelerated through that dead spot to make it much less pronounced.

Its hard to make the M104s in general run perfect, they always have little issues here and there, thats just a part of their character they just don't really open up until 4000rpm.

ob1kenobi

yes that could also be the problem.

BongC36

Thank you for your replies gentlemen. I will be checking on the overload switch, CPS and Cam sensor this weekend, I haven't thought of those.

It doesn't feel like a flat spot, and it wasn't there when the car was new. I'll try to describe it. From stand-still I floor the throttle. In 1st gear the RPM will shoot right thru the 3200 rpm mark and slam into 2nd at around 6500 RPM, still climbing rapidly. Then at around 3200 rpm the climb will almost STOP, inching up then at around 3500 rpm there will be a burst of power accompanied by the characteristic ripping canvass sound of the 104 and shoot to 4000~4200 rpm at which point it will pause again for a second then there will be another burst of power and it will slam-shift into 3rd at around 180 kph/6500 RPM. From there the climb to 260 kph/fuel cut-off is smooth and rapid. BTW when I baby the throttle there is NO hesitation.

The thing is, it doesn't do this every time, although the flat spot at 3200 rpm is always present now, but not when the car was new. I have 68,000 kilometers on the car. I use RON 96 fuel + additive to increase it to above 98 RON. RON 96 is the best fuel that we can buy here.

Please explain further what are the symptoms of a failing Cam Position Sensor? I had a CRANK position sensor fail on my SLK 320 and the symptom was NO START when hot.

jayrasheed

Its worth looking into the CPS but usually when that goes bad it gets hard to start the car and it will need 3 to 4 crank overs before it fires up.

From what ur describing i am almost sure its the Overload thing, cause that’s what i have on my 1995 W140 but at 4000+ and 5000+ but still exact same thing.

On my AMG its just real flat spot and its annoying as hell.
To explain, the overload switch should only activate when shifting from first to second, i dont know if it activates from second to third.
Any way when it activates it retards the timing map to reduce power and save the gearbox. what i assume is happening is that the switch is messed up and its thinking your regular oil pressure in the gear box under hard acceleration is the shift point.

on my car when i drive very hard for a few min it develops a similar issue to urs at abt 5000rpm but still not as severe as ur case.

AMS Performance

I would highly recommend getting the BG fuel injector cleaning service done. Most shops will do it for like $150. It will REALLY clean out your entire system and help the car run much much smoother. Its worth a shot b/c your injectors are probably getting plugged up after 12+ years of use.

jayrasheed

i had my injectors cleaned and it didnt do much. But still i clean them every 30k km on all my cars.
Ironic is that my car today is staring to develop same issues like bong here now i have mini flat spots at 5k rpms

BongC36

I'm sorry to hear that the your car is developing the same thing Jay. I asked my mechanic to buy the Cam Position Sensor and the Transmission Overload switch. Once they arrive I'm going to swap them in an advise you of the results.

AMS, I had my injectors cleaned and tested late last year. There was one whose spray pattern was dissimilar to the others and we replaced it ($$$!) but no significant change noted.

jayrasheed

Thanx man,
yup and its gettin worse by the day. in third mostly u feel it and its f!@#Ing annoying

Guess ill be fixing it mid next week, if i get the free time.
waiting ur updates

BongC36

2 months ago, my 95 C36 suffered from a random malfunction where the engine speed stops at 1500 RPM, sort of a limp-home mode. The car would jump and jerk as the computer shuts off the fuel at exactly 1500 RPM then goes again at 1200 rpm

This is on top of a 4-year old problem of a flat spot from 3200-3500 RPM that we had been unable to solve by MAF, spark plugs, coil, wiring harness replacement etc.

I read a post that the Electronic Throttle Actuator (ETA) or its wiring might be at fault so I tried opening the wiring lead going to the ETA. That darned insulation of the wires inside had crumbled to dust and the bare wires are actually touching!

I found an excellent post how to fix this in another forum and replaced the wires individually and I was pleasantly surprised that not only is the 1500 RPM trap gone, the flat spot or hesitation at 3200 rpm is gone as well! Not bad for a weekend afternoon's work

503C43 ////AMG

The MB dealership will not do this for you, they told me that they do it for regular Mercedes but NOT AMG engines. They absolutely refused to do it for me, I assumed that they were telling the truth as they had a paying customer there (me) begging to pay the $150 to get it done but they wouldn't take my money.

BrabusCClass

Try using 100 octane and going on a nice long drive. Its fun and maybe that will help clean out the system. I used to use fuel injector cleaner and go for 200+ mile drives too.

ProjectC55

Great find man. I'm glad u resolved the issue. This should help alot of folks here.

nzbmc

Replace the Over Voltage Protection Relay! It's an easy DIY replacement. All your dreams will come true.