AMG E55 with Very Odd Electrical issue, Appears to be Bad MAF, but isn't.
 

I have a C43 with a E55 engine(2001) the car runs great up until about 4 months ago. I started to get PO170 and PO173 codes along with PO446.

I had been upgrading the car chassis and sensors all summer long to bring the car back up to close to new spec. Replaced all the subframe bushings, control arms bushings, etc.

On the engine I repaced the Crankshaft and Camshaft sensors, the MAF and cleaned the MOT valve in the engine bay. I also repaced the four O2 sensors. I keep getting the PO170, PO173 and PO446 codes.

So Booked an hour or two at the dealer to see what they could find. MAF was reading 1.1 volts and giving out a 4kg/hr reading for air flow and the injectors where outputting enough fuel to keep the motor very rich. Plugged in a brand new MAF off the shelf and got the same readings 4kg/hr or minute, spec is around 16 to 18kg/hr or minute. We went through all the electrical lines as they run from the MAF connector to the ECU and all of them checked out with no shorts, resistance, etc. In short the MAF wiring was in good shape.

Any clues as to what would cause the MAF to read such low air mass readings, with the O2 sensors working correctly and the wiring being sound?

At 4kg/min or hr the car should not even run.

Last thing, with the key in the on position the fuel pump does not prime the system, so 0 psi at the rail. With the engine on, the fuel pressure jumps to approx. 400 kpa or 58psi. The charcoal cansister valve behind the rear wheel fender cover will click on and off when given a test voltage of 12 volts.

Anyone have any suggestions?

Sincerly, Jeff

Are you sure the MAF that they installed is a good one?


I cannot remember the error code, but I was getting a check engine light, and the codes were for the MAF. I replaced the MAF in the C220 with one from the dealer, and it still flagged the Check Engine light. Got a replacement for the replacement, and the check engine lights went away.

iwrock,

After the new off-the-shelf MAF was tried on my engine with the same results that my MAF was reading we swaped it into another 55 engine to see the MAF reading. It came right up to the spec of 18kg/hr-min of air mass.

So at that point we were 99.9% sure that the MAF was not cuasing this issue.

Thanks for the reply.

Jeff

i had 1 car that posted p0170/0173 that needed the amm, vacuum leaks resealed and a new fuel filter to correct a low pressure problem. usually it's 1 of those that fixes the codes, not all 3. good luck, chuck.

Well I am still trying to fix the Check Engine Light(CEL) issue. I have replaced the MOT vlave that allows the gas vapors to be transmitted to the intake manifold, but that did not fix the issue.

I have been cleaning all the ground connections I can find for the car and while it did not fix the CEL it has made a real difference in the way the car runs. It is much smoother at idle and much more responsive while underway.

Seat of the pants would tell you that the motor is up some 20+Hp.

I would like to know where all the ground connections are as this is really worth the effort based on these last few days.

I have the Purge Valve on order that sits on the charcoal canister and will replace that as well as most of the relays.

I hope one of these two items will flush out the issue and fix the problem.

Jeff

If all else fails, the PCM could be the issue but rare that a PCM goes bad out of the blue