Fuhsm1

Hey everyone. Love the community advice from this forum. My first time posting.

2007 E320 Bluetec, V6 diesel. 118,000 miles. I want to see if anyone recognizes this issue:

Engine code P0101 on, likely saying "something" in intake is wrong. Not sure what yet. New MAF/intake pipe, new boost pressure sensor, new pressure relief valve. All OEM parts.

Car builds boost during normal driving. After I let off gas pedal, car goes into "limp home mode", barely accelerates on flat road. Pressure normally 30+ psi. After this, pressure barely reaches 20 psi. Note this is total pressure which includes atmospheric 14.7.

Note, if I first shift into N then let off gas pedal, problem doesn't happen. If problem does happen, and it's in LHM, I turn key off and then back on again to fix.

Any ideas? I hate guessing and just throwing $$$ parts at a car and still have the same problem.

marc hanna

I would start by checking to make sure everything was fitted up properly and that there are no cracks or splits in the intake.

Fuhsm1

Ok, thanks for the advice, I will test all hoses, couplings, intake manifold, etc. for leaks. When I got the car, about 3 months ago, this problem only happened in the highway (at full load). I then repaired a small leak on the hose between intercooler and engine. Now the problem happens every time I drive it. Perhaps pressure sensor is telling the ECU something different than the MAF, something like that. I will report back results.

Do the CDI / Bluetec V6's have a "BOV" type of device, meaning something that relieves pressure spikes that occur when you first release gas pedal? That's where my troubleshooting mind is stuck on. I know diesels don't use throttle bodies like gas engines, but these engines do have a similar throttle "actuator" flap in beginning of intake manifold.

Forgive me, long time gas engine guy, this is my first diesel. Very interested in learning.

marc hanna

Not that I know of. Yes, they do have a butterfly valve, but throttle is backed-off by reducing the amount of fuel injected into the cylinders. These are quite a bit different than diesels with conventional injection pumps.

When you replaced the MAF, did you replace the cartridge only, or the whole assembly?

Fuhsm1

Ok, simple enough. That clears one theory :-)

I replaced both MAFs and the intake "Y-pipe", clamps, and seals. They all came together from Mercedes assembled. Took 5 minutes of my time to swap.

Note - the P0101 check engine light was not on until I first removed the original intake tube to check for leaks and clean it. Maybe one of the wire connectors or engine harness which runs under turbo inlet has a short.

I know, I need to take this one step at a time. I appreciate your responses so far!

Fuhsm1

Both issues resolved. Here's how:

Issue #1: Thanks goes to Marc Hanna. I had leaks in my charge air piping, between the intercooler and intake manifold. I replaced the thick o-ring between the intake pipe flange and manifold. Original one was torn. I also replaced both intercooler rubber tubes as there were slight leaks that occurred under boost. I found these after I hooked my air compressor to my intake pipes and listened for leaks. Thank you!!

Issue #2: I have a shorted MAF sensor plug on the engine harness. Resolved by putting a single 1/2" long strand of bare wire, bent in half, into the harness side of the MAF plug. Did this on each of the 4 female terminals, on both left and right MAF sensor plugs. I reset check engine code, and it has been off since. No more problem.

marc hanna

Glad to hear you got the problem fixed. Happy New Year!

Carsy

Good result.