TTA850

After a week in the local dealer I get the car back and they tell me they dont know whats wrong but think it may be something in the harness. The problem I've been having is a loss of power and the motor seems to struggle to rev over 2500rpm or half throttle. I've replaced the plugs and wires and it's had a B service about 1K miles ago. I've replaced the MAF sensor after noticing the sluggish performance and decreased gas mileage, which has improved but performance continued to decline. I got a check engine light once for codes P0300, P0301, P0302, P0303, and P0304 but the car doesnt seem to have a miss. I reset the codes because I needed to get an inspection and they havent come back yet - even when I try to duplicate the conditions. Normal driving the car runs smooth and perfect.

I belived the problem to be the cats but the dealer checked the cats and even said they dropped the exhaust with no change, they also ran full diagnostics on the engine, transmission, MAF sensor, and engine management unit which they said all came back ok. I did a backpressure test on the cats before it went in and did get some pressure, at idle about 0.5-1psi and spikes up to 5.5psi during snap acceleration. To me the cats are partially clogged but they passed the dealers 4 hour diagnostic so I'm looking elsewhere now but come up short. I've quickly checked the crank position sensor plug as per the technical service bulletin and didnt see any corrosion but wouldnt rule that out.

The car is a 2000 E55 with 64K miles, any ideas or help would be greatly appreciated.

Thanks in advance,
Steve

MaxVon

Hi Steve,
I can relate to your situation. Please check out my thread...

https://mbworld.org/forums/w210-amg/236303-slow-e55.html

The catalytic converters will throw the P0300, P03** codes. My car passed emissions testing and smog in CA and MA with a bad cat so I thought that couldn't be it. Low and behold it was. On top of that the MAF was bad as well.

Your back pressure values indicate restriction. Find a dealer that will work with you to replace your cats under the 8 year 80K warranty.

Good Luck.

Max

henryclk

general specs for backpressure is no more than 1/2 psi(.5) at 2000 rpm.
your readings indicate you likely have plugged cats. this could and most of the time does cause misfires.. removing the post cat o2 sensors and installing a backpressure guage will give you the difference in the amount of exhaust restriction(if pressure is less behind the cats, the cats are plugged)
hope this helps

TTA850

Thanks guys, based on my readings and symptoms I really do feel I have a cat issue but was looking elsewhere because of what the dealer said and the fact that it passed emmiaions - but knowing it can still pass even with a bad cat I'm going to look at them again.