P38 dhse no power but only in reverse?

Stig1 · Feb 9, 2020

V

Datatek said:
Pull the pipe off the inlet manifold and look see if the EGR valve is jammed open.
Check the turbo is working.
You really are tilting at rainbows without diagnostics.

I've got diagnostics hawkeye and it's not showing any faults . The egr isnt stuck open and I've tried it with the pipe blocked off and it's the same

Dopey · Feb 9, 2020

Datatek said:
It will not make a difference between forward and reverse. Voltage varies with manifold pressure.

You say that but I had that problem for 5 or more years no one knew what it was, I changed the map sensor and it cured the problem, it was crap at acceleration as we, and it cured that also

Stig1 · Feb 9, 2020

The only thing that's looks out of spec now is the map sensor

Dopey · Feb 9, 2020

Stig1 said:
Bit of a update on this I've found out today it's not only reverse it's also forward as I went to get up a kerb and it would not pull up it at all I had to select low range . Wonder if this is linked to why it feels flat going up hill ? Tried unplugging the MAF and makes no diffrence

If the MAF is broken.... and then pulling it out makes no difference, then its broken

Dopey · Feb 9, 2020

I got 2 cheap ones from Ali Express, (about 5 years ago) and I am still using the first one, so not all stuff is crap from them

Stig1 · Feb 9, 2020

Think I've found the issue just took the map sensor off and there was a thick black goo in there washed it out with some brake cleaner and it seems to pick up much better . My question is what sort of issues will this being blocked normally cause thank you for all your help

Dopey · Feb 9, 2020

Stig1 said:
Think I've found the issue just took the map sensor off and there was a thick black goo in there washed it out with some brake cleaner and it seems to pick up much better . My question is what sort of issues will this being blocked normally cause thank you for all your help

It wont work....... lol

Datatek · Feb 9, 2020

Stig1 said:
Think I've found the issue just took the map sensor off and there was a thick black goo in there washed it out with some brake cleaner and it seems to pick up much better . My question is what sort of issues will this being blocked normally cause thank you for all your help

You need to check the pipe and the manifold spigot are also

Dopey said:
If the MAF is broken.... and then pulling it out makes no difference, then its broken

Not so Dopey, unplug a good MAF and it makes little difference. However if the MAF has failed electronically,unplugging it may improve things.

Grrrrrr · Feb 9, 2020

Stig1 said:
Think I've found the issue just took the map sensor off and there was a thick black goo in there washed it out with some brake cleaner and it seems to pick up much better . My question is what sort of issues will this being blocked normally cause thank you for all your help

Mass airflow pressure. So it measures the amount of air going in from the turbo. Without it it has no idea how much air goes in so presumably assumes atmospheric and limits fuel.

Datatek · Feb 9, 2020

Stig1 said:
Think I've found the issue just took the map sensor off and there was a thick black goo in there washed it out with some brake cleaner and it seems to pick up much better . My question is what sort of issues will this being blocked normally cause thank you for all your help

Maybe you should be able to see the MAP pressure readings on Hawkeye live data, you can on Nanocom and Faultmate

Grrrrrr said:
Mass airflow pressure. So it measures the amount of air going in from the turbo. Without it it has no idea how much air goes in so presumably assumes atmospheric and limits fuel.

It does measure the air into the turbo, but the MAP measures pressure. The M51 will run with the MAF disconnected.

Grrrrrr · Feb 9, 2020

Datatek said:
Maybe you should be able to see the MAP pressure readings on Hawkeye live data, you can on Nanocom and Faultmate

It does measure the air into the turbo, but the MAP measures pressure. The M51 will run with the MAF disconnected.

You mean air pressure into the engine from the turbo, surely?

Stig1 · Feb 9, 2020

I can confirm it has cured my fault car is all ok now thank you for your help everyone

Datatek · Feb 9, 2020

Grrrrrr said:
You mean air pressure into the engine from the turbo, surely?

The MAF is between the air filter and the turbo inlet, thus it measures the air volume being drawn in.
The MAP measures pressure in the manifold but not volume.

Rubberknees · Feb 9, 2020

Good result. Sometimes the smallest things can cause a problem

Grrrrrr · Feb 10, 2020

Datatek said:
The MAF is between the air filter and the turbo inlet, thus it measures the air volume being drawn in.
The MAP measures pressure in the manifold but not volume.

Oh, I see where you are coming from. Yes, measures pressure.

tomcat59alan · Feb 10, 2020

Grrrrrr said:
Oh, I see where you are coming from. Yes, measures pressure.

Hence Manifold Absolute Pressure sensor.

Grrrrrr · Feb 10, 2020

tomcat59alan said:
Hence Manifold Absolute Pressure sensor.

Yeah, I thought that was self evident in the name. If you compress the gas there will be more oxygen in a given volume to burn.

Stig1 · Feb 15, 2020

I give up with this car it's back to how it was but I didnt really drive it after I cleaned out the map line and sensor . So I brought a new map sensor today and it's still the bloody same I'm losing the will with it now

Datatek · Feb 15, 2020

Stig1 said:
I give up with this car it's back to how it was but I didnt really drive it after I cleaned out the map line and sensor . So I brought a new map sensor today and it's still the bloody same I'm losing the will with it now

Have you checked that the MAP pipe is clear and not blocked at the manifold?
Do a fuel flow check at the filter.

Stig1 · Feb 15, 2020

Datatek said:
Have you checked that the MAP pipe is clear and not blocked at the manifold?
Do a fuel flow check at the filter.

Yes the sensor and the line to the manifold are new and I cleaned the outlet from the manifold with some brake cleaner and I've picked up a new bosch fuel filter this afternoon

P38 dhse no power but only in reverse?

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