NikTheGeek
New Member
I'm out of my depth
but that bits true as several people who have had their EGR diesels on diagnostics (inc me) have a temp reading of -38.8
I'm out of my depth
but that bits true as several people who have had their EGR diesels on diagnostics (inc me) have a temp reading of -38.8
I'm out of my depth
Yes it is a preset in the ECU to make sure the EGR system always works.
Datatek
Well-Known Member
The diagnostics read -38.8 because there is no sensor to read and the diagnostic software defaults to -38.8
Datatek
Well-Known Member
I had a technical paper that explained in relatively simple terms the introduction and application of EGR to diesel engined cars, unfortunately I lost it when my computer went and scrapped the HDD.
Roughly, the impending EURO 1 & Euro 2 emissions regs were the driver for the implementation of EGR although experiments had been carried out in the early 70's..
Some manufacturers managed initially to apply EGR without a MAF, this was quickly superceeded by the adoption of MAF control for the EGR.
With the adoption of Euro 2 in 1996, the MAF was incorporated into software controlled fixed fuelling maps in the EDC to give closer control of fuelling in the pre boost phase of running, up to about 2500rpm on the M51. As soon as sufficient positive manifold pressure is detected by the MAP, the MAF becomes irrelevant for fuelling as it is assumed that there is always an excess air situation, at this point control of fuelling is by the MAP and other sensors and the embedded software maps in the EDC, the MAF being used just for EGR.
There is plenty of evidence to show that this applies to the M51 as the EGR was introduced by LR in 1999 when Euro 2 was already in force.
Look at BMW forums and problems with the MAF causing poor low end performance and fuel consumption. On my car, unplugging the MAF affects the running, not like a petrol, but it becomes more sluggish than normal. I have the EGR disabled so the MAF should have no function if your theory is correct.
The same applies to VAG and Mercedes, a duff MAF affects low end performance.
Roughly, the impending EURO 1 & Euro 2 emissions regs were the driver for the implementation of EGR although experiments had been carried out in the early 70's..
Some manufacturers managed initially to apply EGR without a MAF, this was quickly superceeded by the adoption of MAF control for the EGR.
With the adoption of Euro 2 in 1996, the MAF was incorporated into software controlled fixed fuelling maps in the EDC to give closer control of fuelling in the pre boost phase of running, up to about 2500rpm on the M51. As soon as sufficient positive manifold pressure is detected by the MAP, the MAF becomes irrelevant for fuelling as it is assumed that there is always an excess air situation, at this point control of fuelling is by the MAP and other sensors and the embedded software maps in the EDC, the MAF being used just for EGR.
There is plenty of evidence to show that this applies to the M51 as the EGR was introduced by LR in 1999 when Euro 2 was already in force.
Look at BMW forums and problems with the MAF causing poor low end performance and fuel consumption. On my car, unplugging the MAF affects the running, not like a petrol, but it becomes more sluggish than normal. I have the EGR disabled so the MAF should have no function if your theory is correct.
The same applies to VAG and Mercedes, a duff MAF affects low end performance.
Datatek
Well-Known Member
I agree that not all of that copy and paste applies to the M51, in particular the starting, but my other post does.
Not very much of it actually. http://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=658025
Datatek
Well-Known Member
I've seen that, but the M51 as installed in the P38 does not have AGR (EGR) feed back or the filter, it applies to the M51 in the BMW. It also does not specifically cover fueling.Not very much of it actually. http://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=658025
A clear identifying feature on engines with AGR feedback control.
Transits have EGR feedback which means you cannot just disconnect it as it flags a fault.
Of course it does what do you think the MAF is for? I keep trying to explain but you won't listen.
Datatek
Well-Known Member
AGR feedback is an electrical connection to the EGR valve in my experience that indicates when the valve has mechanically opened.Of course it does what do you think the MAF is for? I keep trying to explain but you won't listen.
If the MAF was been used as the feedback loop, it would flag a fault if when the EGR was called no change in airflow occurred due to the EGR being blanked.
I have to say that hundreds disagree with your explanations judging by other sites.
Keith i have already explained the feedback loop. The MAF is there to monitor and fine control the EGR. When the EGR opens and exhaust gas enters the manifold the flow through the MAF reduces. The ecu then knows how much % EGR is being applied. The ECU then modulates the vacuum valve to increase or decrease the % of gas entering the manifold within mapped tolerances, for the engine speed, throttle request and engine load. It can judge this from increasing or decreasing MAF flow readings. That is the feedback loop. Fuelling may change in this process but that is as a consequence of the ECU trying to maintain the engine RPM requested by the throttle position pot. And not because of flow measurements from the MAF.
Datatek
Well-Known Member
So, when EDC commands the EGR to open, the MAF measures this. If so, when the EGR is blanked and fails to open on command the EDC should recognise that there is no difference in airflow through the MAF and log a fault as it does on cars that really have closed loop feedback If it fails to do this there is no feedback loop.
We all know that you can block the EGR with no effect on the EDC unlike some vehicles, so control is open loop.
So it's good news, as the MAF only controls the EGR and you can block the EGR with no fault occurring, we can all block the EGR and ignore the MAF as it cannot affect the running. Just as long as it's plugged in it cannot affect in any way the way the engine runs with the EGR blocked
I must relay this important news to all the Bimmer VW and Merc sites that stupidly think the MAF is causing problems.
So, when EDC commands the EGR to open, the MAF measures this. If so, when the EGR is blanked and fails to open on command the EDC should recognise that there is no difference in airflow through the MAF and log a fault as it does on cars that really have closed loop feedback If it fails to do this there is no feedback loop.
We all know that you can block the EGR with no effect on the EDC unlike some vehicles, so control is open loop.
So it's good news, as the MAF only controls the EGR and you can block the EGR with no fault occurring, we can all block the EGR and ignore the MAF as it cannot affect the running. Just as long as it's plugged in it cannot affect in any way the way the engine runs with the EGR blocked
I must relay this important news to all the Bimmer VW and Merc sites that stupidly think the MAF is causing problems.
On a P38 you can which is the vehicle we are talking about. Is there a fault logged on your P38 with the EGR blocked? If the MAF goes tits up it can cause one of two things no signal shuts EGR down or a bad signal can cause over use of EGR causing running problems. No power and black smoke being one of them.
Datatek
Well-Known Member
You missed the point again.
MAF goes tits up shuts EGR so no problem there then, same effect as if you block the MAF and no there is no fault logged with the EGR blocked so there is no feedback of EGR operation.
A bad MAF signal causes running problems even with the EGR blocked so if the EGR cannot operate, a bad MAF signal should have no effect, but it does.
You are about 10 years behind the times on MAF operation. Euro 2 came in around 1996.
MAF goes tits up no problem is there not? Connect your MSV up to your car and disconnect the MAF, post back what fault message you get. Euro 2 was implemented by Land rover in 1998 with there own little slant on things.
Datatek
Well-Known Member
Disconnected is not the same as faulty and there is no fault message.
As I said, with the EGR blocked, disconnecting the MAF affects running in the pre boost phase. According to you it should have no effect because it only controls the EGR.
You can't have it both ways, if the the MAF only controls EGR, blocking the EGR means the MAF has no function, so disconnecting it should have no effect as there is no feed back loop.
To meet Euro 2 MAf started to be used to control fueling off boost, on boost it's not needed as there is excess air.
EGR reduces excess air and so reduces combustion temperature which in turn reduces Nox emissions, but you know that.
Just to clarify. If the car is run with MAF disconnected you will get "Fault low air flow". Fault logged. Current. Basically means EGR is none functional. The air flow function is in a closed loop for EGR control within the EDC ECU. It has no direct control of fuel quantity. The engine is throttled by fuel quantity not by air quantity. Therefore any change in engine RPM is controlled by fuel quantity adjustments and not by air quantity adjustments.
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