High Exhaust Back Pressure

[mibo]

I've just purchased an ML350 and had a few issues with limp mode. The turbo and dpf sensor has been replaced but it doesnt feel like its driving quite right. Any diesel Ive had in the past Ive felt the turbo kick in, but on this car I need to rev hard to get a boost.

I plugged in my icarsoft reader for my drive home yesterday and I'm getting exhaust back pressure readings of 1.2 bad at idle and up to 4 bar when driving. Are these values normal? I think it was going into DPF regen very frequently too.

The car is a Mercedes ML350 Bluetech 2011

 

[brandwooddixon]

Seems a bit high to me. Are you sure that the dpf isn't blocked?

 

[mibo]

Seems a bit high to me. Are you sure that the dpf isn't blocked?

No thats my best guess and plan on booking it in for a Halford deep clean to see if that helps, depending on answer here

 

[onefortheroad]

1.2 is around atmospheric pressure at sea level . You can expect over 3 to 4 under load.

 

[mibo]

1.2 is around atmospheric pressure at sea level . You can expect over 3 to 4 under load.

OK so behaving normally then.
Thanks for responses

 

[onefortheroad]

OK so behaving normally then.
Thanks for responses

A failed sensor shows well over 4 bar at tick over. Causes kangerooing and limp at around 3000 rpm.

 

[mibo]

A failed sensor shows well over 4 bar at tick over

At idle its only about 1.2 bar vs 1 bar intake pressure. Its only hitting 4 bar under full load.
Cruising at 70mphits 1.6 - 2 bar.

It does seem to go into regen frequently though, but not sure if the icarsoft is giving me nonsense readings. The air temp upstream of the turbo increases to 650 ish when the total filter content reaches 7g. It only takes about 5 mins to reach this level though.

 

[w204benz]

If you're concerned about the DPF, it's the differential pressure you should be looking at.

Below 10 millibar at idle and below 80 millibar under load would suggest it isn't blocked.

 

[supernoodle]

If it thinks the ash content is high it will regen more frequently. You should be able to read that on icarsoft.

 

[mibo]

If it thinks the ash content is high it will regen more frequently. You should be able to read that on icarsoft.

It did say 3g but now it says 0g so not sure its giving me any sense.
Will check the dp later this afternoon on school pick up.

 

[onefortheroad]

It did say 3g but now it says 0g so not sure its giving me any sense.
Will check the dp later this afternoon on school pick up.

Did you reset anything?

 

[mibo]

Did you reset anything?

No, it just seemed to in to regen

 

[mibo]

If you're concerned about the DPF, it's the differential pressure you should be looking at.

Below 10 millibar at idle and below 80 millibar under load would suggest it isn't blocked.

So I got between 12 and 250 driving a few miles up the road

 

[onefortheroad]

So I got between 12 and 250 driving a few miles up the road

You should be seeing as close to zero at tickover. , - 0.04 to + 0.04

 

[mibo]

You should be seeing as close to zero at tickover. , - 0.04 to + 0.04

I just got 806 flooring it at 20mph to 40mph

 

[onefortheroad]

I just got 806 flooring it at 20mph to 40mph

Unsure what measurements your using tbh. It's at tick over you'll see the figures I quoted , basically it's free to suck and free to blow .

 

[mibo]

Unsure what measurements your using tbh. It's at tick over you'll see the figures I quoted , basically it's free to suck and free to blow .

mbar

 

[onefortheroad]

Flooring it from 20 to 40 lol.

Whooooooshhhhhh !!!¡!!!! Ha ha . Love it

12 mbar is 0.17 psi which is fine

 

[mibo]

Flooring it from 20 to 40 lol.

Whooooooshhhhhh !!!¡!!!! Ha ha . Love it

12 mbar is 0.17 psi which is fine

Is the 806 mbar normal too?

 

[onefortheroad]

Is the 806 mbar normal too?

No idea . I just check that at idle .