OM642 fuel rail pressure circuit high and boost sensor circuit low

[Tvart]

Hi all, bought my 2006 CLS 320cdi a few weeks ago and have had trouble with it dropping into limp mode and even cutting out completely a couple of times! I hope I have solved the cutting out issue as last time it did it it wouldn't start untill it cooled down so I changed the crank sensor. But now it's still dropping into limp mode. I have already changed the fuel quantity valve as I thought it could be the problem. Also tried another cam sensor and have had the wiring out and checked from the bulkhead to just passed the turbo. Is it worth trying a fuel pressure sensor or boost sensor? When I logged the data from torque pro app when it dropped into limp mode at idle soon after start it looks maybe like the rail pressure spiked, or was that the engine anti stalling, I'm not sure. Any ideas anyone?! Love the car otherwise! Cheers

 

[mersum1es]

Pressure cant be right... 80000PSI (what 5500bar) - not likely. Even 'normal' level 3000PSI (2000bar) is about max system pressure.

What fuel pressure show when car is stopped a while?

You has SDS, did you do all individual tests (hp pump, fuel quantity valve, pressure regulator valve, boost pressure, egr, intake manifold flaps) etc?


Do you have voltage/grounding problem, plenty of no signals/too high signals same time is weird..

Stop palying parts darts

 

[Tvart]

Pressure cant be right... 80000PSI (what 5500bar) - not likely. Even 'normal' level 3000PSI (2000bar) is about max system pressure.

What fuel pressure show when car is stopped a while?

You has SDS, did you do all individual tests (hp pump, fuel quantity valve, pressure regulator valve, boost pressure, egr, intake manifold flaps) etc?


Do you have voltage/grounding problem, plenty of no signals/too high signals same time is weird..

Stop palying parts darts

That measurement is in Kpa not psi. The Star screen is from my Mercedes specialist

 

[Tvart]

Hi the values shown are Kpa not psi, I check them at ignition, idle and full throttle a d they are about correct. What I'm not sure of is the spike just at idle. Is there many more tests Star can do to help find the problem, like Injector leak down etc?

 

[mersum1es]

ok units was my bad... peak points either quantity valve or regulator. There would have been test for them in SDS, fuel quantiry valve test measures especialy pressure peaks. Like said turbo actuator test, EGR test, MAF, intake manifold flaps are are related to boost and circled to fuel (engine is basically pressure controlled, simplified if more pressure is asked fuel injection is increased).

Injector leak test is not needing any test device, just hose and if needed a bottle per injector. Electrical correlation values are seen in SDS and they alone can pinpoint worn injector.

 

[Tvart]

ok units was my bad... peak points either quantity valve or regulator. There would have been test for them in SDS, fuel quantiry valve test measures especialy pressure peaks. Like said turbo actuator test, EGR test, MAF, intake manifold flaps are are related to boost and circled to fuel (engine is basically pressure controlled, simplified if more pressure is asked fuel injection is increased).


Injector leak test is not needing any test device, just hose and if needed a bottle per injector. Electrical correlation values are seen in SDS and they alone can pinpoint worn injector.

Oh that's interesting as I have disconnected the swirl flap motor as it was blowing the fuse for the circuit as oil contamination from the turbo seal was all over the flap motor. I put in a resistor and left unplugged. I can take the car back to the specialist and ask them to run the tests also.

 

[mersum1es]

If flap linkages are broken and they are in closed position, that probably triggers fault at higher revs when they should be open. But if they are connected to motor, motor unit spring should force them always open.

Have you cheked out what condition your turbo seals are, if it drops oil heavily...

 

[Tvart]

If flap linkages are broken and they are in closed position, that probably triggers fault at higher revs when they should be open. But if they are connected to motor, motor unit spring should force them always open.

Have you cheked out what condition your turbo seals are, if it drops oil heavily...

The fault always happens at idle or low rpm. The oil is not that bad as since I cleaned it up it hasn't dropped much more think it's just built up. Car pulls really well when it's not in limp mode. But it is smoky in the first start, and the glow plug light does stay on for a while after start. It's had new plugs and control unit on it when I bought it.

 

[Tvart]

I think I may have found the issue. When In limp mode there doesn't seem to be 5v at the boost sensor and it reports boost to be the same as of the sensor wasn't there... -0.6 bar so less than no turbo pressure. Is there a relay for these two sensors, they seem to get 5v from the same purple/green wire.

 

[Danspain]

Hello, I am new to the forum.
Came here to discuss ml headlamps but having seen this post I feel compelled to share.
I had the same thing exactly on my ML 270, two months ago, same fault report.
The vehicle seemed to cut out for no reason.
Long and the short of it was injector bypass. I had all 5 injectors serviced by a company here in spain and it has been fine since.
Hope this helps.
Cost was €240.00 including indy and DHL charges.

 

[Tvart]

Hello, I am new to the forum.
Came here to discuss ml headlamps but having seen this post I feel compelled to share.
I had the same thing exactly on my ML 270, two months ago, same fault report.
The vehicle seemed to cut out for no reason.
Long and the short of it was injector bypass. I had all 5 injectors serviced by a company here in spain and it has been fine since.
Hope this helps.
Cost was €240.00 including indy and DHL charges.

Hi Dan that's great thanks. I currently have the ECU out getting swapped over to a new used one to check if it's that, but I shall get the Injectors checked/serviced also. Ths strange thing is the boost pressure sensor reading going all the way down to -0.6bar pressure when it happens, so mu thought was it's cutting fuelling to match

 

[Danspain]

Hi Dan that's great thanks. I currently have the ECU out getting swapped over to a new used one to check if it's that, but I shall get the Injectors checked/serviced also. Ths strange thing is the boost pressure sensor reading going all the way down to -0.6bar pressure when it happens, so mu thought was it's cutting fuelling to match

Yes, mine gave the same readings.
No fuel pressure, turbo over boost, all sorts
It gets worse, at one point it just died on me @ 120kmh on the freeway, accelerating to pass another vehicle.... scary
Fortunately spanish motorways never get too busy outside of cities, and everyone's familiar with people just pulling across the lanes here. Haha.

 

[Tvart]

Well i thought i would update this if anyone is getting similar problems, turns out the ECU was malfunctioning randomly. This my be to previously chaffed wires under the engine cover that had since been repaired. However a swop of ECU to a known good used unit (by ECU Doctor - the only ECU specialist that would touch the Bosch Mercedes ECU with an intermittent fault) all is fine and has been so for a few months now. If you have random readings at sensors that done seem to make sense adn you have tried everything else, then get your ECU swopped or at least checked!