P38A DSE autobox - ideas please. It was going too well.... SOLVED

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Datatek said:
The MAF sensor has nothing to do with how the engine runs.
You cannot have it both ways, a duff MAF can certainly affect how the engine runs by if only by causing the EGR to malfunction.
I would be interested to know why it caused the loss of power with the EGR blocked.
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Ok give us your version of what the MAF sensor does. EGR malfunction is just one possibility. Obviously if the EGR is blanked then it cannot be that. Actually if there is a fault with the MAF sensor EGR is disabled. But a faulty MAF sensor can cause the ECU to lose the plot as demonstrated in previous posts. At least BMW service bulletins say it can, maybe you know more than they do. Please enlighten us.
 
wammers said:
-38.88 degrees is the preset IAT on the EGR equipped P38.
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That figures Tony, while the engine is running it should normally reflect within reason the outside temp. Thats where mine doesn't... Engine warm or cold.
So logic says I have no live reading/communication from the iat to the ECU..

But.... Why run perfectly and sometimes run with power loss and again as if there never was an issue??
 
Mark Piercy said:
That figures Tony, while the engine is running it should normally reflect within reason the outside temp. Thats where mine doesn't... Engine warm or cold.
So logic says I have no live reading/communication from the iat to the ECU..

But.... Why run perfectly and sometimes run with power loss and again as if there never was an issue??
Click to expand...

ECU takes a reading from the MAF sensor which in combination with fuel and ECU temp sensors minutely adjusts fuel volume.
 
Mark Piercy said:
Speaking of MAF sensor units. I had a loss if power last evening and a reading of -38° when I plugged it into my maxicom this morning.. but it ran perfectly today offroading and on a 30 minutes round trip this evening??
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Not used. That's a default value. All EGR engines should have that reading. Unless I am mixing my sensors up. Where's the master? Or is his bed-nurse busy?

EDIT. Just seen he's answered further down!
 
Datatek said:
What, the MAF affects fuel volume:eek:
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Yes by a minuscule amount. Together with engine temp and fuel temp readings. The ECU has to know the temperature of the air flowing through the MAF or it cannot obtain an accurate flow reading to use with EGR. It also has to know the engine temp and the fuel temp to make it's calculations for volume.
 
Mark Piercy said:
That figures Tony, while the engine is running it should normally reflect within reason the outside temp. Thats where mine doesn't... Engine warm or cold.
So logic says I have no live reading/communication from the iat to the ECU..

But.... Why run perfectly and sometimes run with power loss and again as if there never was an issue??
Click to expand...

You didn't do your daily sacrifice to the P38 god/goddess did you? That's why :cool:
 
RangeRoller dt said:
You have no IAT as such mark, it's just a figure value in your ecu because they did away with it for EGR. Think I'm better off with old system
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understood, just a base line figure that the ecu follows. not an actual figure...… so that leaves me with no bloody idea as to why this f*cker is doing this.
it does an average of 150 mile a week and very rarely does it. the roads I use very rarely change with the hills and corners and it'll do it when ever it feels like.
cow!:p

Mukiwa said:
You didn't do your daily sacrifice to the P38 god/goddess did you? That's why :cool:
Click to expand...
I sacrifice diesel!!!!:eek:
 
Mark Piercy said:
understood, just a base line figure that the ecu follows. not an actual figure...… so that leaves me with no bloody idea as to why this f*cker is doing this.
it does an average of 150 mile a week and very rarely does it. the roads I use very rarely change with the hills and corners and it'll do it when ever it feels like.
cow!:p


I sacrifice diesel!!!!:eek:
Click to expand...
The ECU does not use that figure, it uses the figure from the MAF, the BBS Faultmate diagnostics have never been updated to give MAF readings. That -38.88 figure is, as far as I can discover, just the figure the diagnostics give for no response from the IAT sensor, it means nothing.
 
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Mark Piercy said:
so that leaves me with no bloody idea as to why this f*cker is doing this.
Click to expand...
cow!:p
Without a scrapper (or ideally working DSE to substitute) I would start systematically unplugging see if it goes. Not easy with intermittent fault :( But may narrow it down

If you unplug MAP and it solves it, may be that for example. You could temporarily block EGR see if it makes difference?
 
Datatek said:
The ECU does not use that figure, it uses the figure from the MAF, the BBS diagnostics have never been updated to give MAF readings. That -38.88 figure is, as far as I can discover, just the figure the diagnostics give for no response from the IAT sensor, it means nothing.
Click to expand...

If you unplug MAF and then use Nanocom you will get a "Air flow fault". So at least Nanocom is aware of MAF although it does not give any flow readings. I have never had a duff MAF, so whether it will pickup any other circuit fault than that i do not know.
 
RangeRoller dt said:
cow!:p
Without a scrapper (or ideally working DSE to substitute) I would start systematically unplugging see if it goes. Not easy with intermittent fault :( But may narrow it down

If you unplug MAP and it solves it, may be that for example. You could temporarily block EGR see if it makes difference?
Click to expand...
You cannot unplug the MAP sensor electrical connection and expect it to run but the sensors do play up. I was talking about the MAF sensor.
 
wammers said:
If you unplug MAF and then use Nanocom you will get a "Air flow fault". So at least Nanocom is aware of MAF although it does not give any flow readings. I have never had a duff MAF, so whether it will pickup any other circuit fault than that i do not know.
Click to expand...
Shame that Faultmate was never updated to give MAF info.
 
Datatek said:
Shame that Faultmate was never updated to give MAF info.
Click to expand...

It does for petrol engines no doubt. But MAF airflow rate means something for petrol engines. It is pretty inconsequential for the P38 diesel. Other than knowing it is operational for EGR.
 
Some very much needed info there, I'll unplug the maf while its running and connected to the autel diag and see if there is a fault showing.
I don't know if the autel will register the fault...
But i can confirm that running it without the maf does lower it's reaction and raises the consumption and so does the map when it's unplugged as well.
Hmmmm...
 
Mark Piercy said:
So logic says I have no live reading/communication from the iat to the ECU..
But.... Why run perfectly and sometimes run with power loss and again as if there never was an issue??
Click to expand...
I'm not saying this is what it is, just trying to give you ideas - my sensors started playing up, thought BECM had dementia or sensors were dodgy. New battery sorted it - logic told me low battery would be constant but was intermittent almost like duff cps when warm.

Also, would exhaust issue perhaps cause EGR/MAF to get confused now and again?


P.S - I think we may have inadvertently trashed another thread :(:D:p
 
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