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Misfires at moderate accelaration

Symptoms: multiple misfires when accelerating moderately, pedal at about ¼ to 1/3 of WOT. Happens all the time no exceptions. As soon as I try to give a bit of gas I get misfires. If I accelerate real easy its fine, I can drive at highway speeds for hours without any trouble as long as I don’t give it much gas, once again if at highways speeds I moderately accelerate I will get misfires. After misfires engine runs very badly, severe vibration until restart then it runs smoothly as long as I don’t accelerate…

It seems to misfire exactly when turbos kick in, after a couple of tests this morning, car was cold, as soon as i hear the turbos spool hesitation and misfires start.

Stored codes are P0300, P0302, P0304, P0307, P0309, P0308, P0310, P0306, P0303, P0305 pretty much all cylinders misfire, both sides.

Further more lately car did not start-up well after shut down at operational temp, this is symptoms of a bad the crank position sensor, I don’t know if it could affect my new misfire problem.

CEL does not go away, even after multiple startups

I don’t think it’s the gas, problem started at ¼ tank, refueled since, problem persists

Usual suspects would be coil packs, sparks, ignition voltage controller, gas pump/filter?, EGR?, cats.

car has 100000km

I think we can rule out some suspects due to the misfires being in both banks, like the cats and maybe coil packs?

Any suggestions appreciated, I will get the car serviced at my local dealer as usual, but I would like to guide them a bit in the diagnosis…

i think ignition voltage module.

Quote:

Originally Posted by biker349 (Post 5762828)

i think ignition voltage module.

I concur. Its the cheapest part to replace at $600 and 5 min of your time.

R.K.

Thanks for the replies, I would of thought that if it was the ignition voltage controller that I would get misfires at startup as well, not only upon acceleration.

The car will be at the dealer next week, I will post the outcome of the repairs, hopefully they will pinpoint the problem immediately and not change a multitude of unnecessary parts before getting it right.

From experience, it is recommended that you change both coils AND the voltage transformer at the same time. The problem is always at higher rpms when the coil system is put to its limits. If one is slightly weak, it will misfire the whole system. All three units must be at 100%. Life is usually at 30-40K miles. It is the poorest engineering design in this whole engine and they haven't fixed it to date. It is the cost factored in having this monster engine. Been there, done that.

My misfires start at 2000 rpm if I press the accelerator at about 1/3, at neutral I can rev at at least 4000rpm without misfires, the problem is only at load/power demand

Quote:

Originally Posted by greekviking (Post 5764667)

Dropped the car at the dealer today, they called back saying that my fuel pressure is way low at 2 bars, they will replace the filter and see if that fixes the problem.

What is the correct fuel pressure anyway?

I believe the V12TT's use variable output fuel pumps, which is unusual. Maybe the controller is at fault? The symptoms do sound fuel starvation / blocked fuel filter though.

keep us posted on the outcome

After installing new filter still very low pressure, They have ordered a fuel pump assembly. None available in Canada so it might take up to 1 week. :eek:

Got the car back today, they replaced the fuel pump control unit

part# 220 540 29 45

Car runs great once again!

Good result. Its not always the coils.

Nick

Problem came back, now the will replace part 003-542-48-18 (fuel pressure sensor), ordered from Germany, 10 days again!!!

Please keep us posted on the outcome

Is it exactly the same problem you had before?

Quote:

Originally Posted by Welwynnick (Post 5804096)

Is it exactly the same problem you had before?

Yes, maybe worst in the sense that I had to be very very gentle on the throttle, what I don't understand is that the original fix work for a couple of days.

Anyways I got the car back, it is working perfectly once more. They replaced the fuel pressure sensor part #463 905 34 00, the relay and wiring for the part.

Voila! :zoom:

Hi slonar21, Is the problem ended?

Yes problem fixed as stated in my last post

Excellent, I congratulate you and I hope does not come back again.

I had a similar issue for my car (W221 S600), and after many of the diagnosis for a long time more than five months, the problem was from secondary air injection (P0410 fault code).

Quote:

Originally Posted by slonar21 (Post 5816306)

Where is the fuel pressure sensor part #463 905 34 00 located?

If I recall it is near the fuel pump

I don’t know, but as stated the replaced the part and its relay

An eBay listing gives some details about the harness needed

"This Listing Contains: 1 X 4639053400 -Genuine Mercedes-Benz Fuel Pressure Sensor -Inline Also Use: (Qty.) 1 X 4635409213 -Wiring Harness (NOT included). New - Genuine Mercedes-Benz 463 905 34 00 / 463-905-34-00 / 4639053400 Fuel Pressure Sensor-Inline."