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LifeOfDesire

2002 525d Hesitation problem

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For a while now I have had a problem with my 525d hesitating a lot when cold and also hesitating when turning left. Recently I discovered that the MAP sensor had literally snapped off almost and was causing the hesitation when turning left, however, it did not solve the hesitation when cold and now it hesitates for at least a second at around 2000-2500RPM. Today it got so bad for some reason that it would barely accelerate, and I had to pull over and pull out the MAF sensor because for some reason that cures it (although it goes into a failsafe mode). I have replaced the MAF sensor entirely so I do not believe this to be the issue. I have done a smoke test, replaced the intercooler to EGR pipe and the EGR is disabled so this is not the issue. I also blanked off the swirl flaps last week so this is not the issue. MAP sensor is new and I have tried driving with it unplugged and it still stutters so that is not the issue.

 

Here is an example of the hesitation, bear in mind it doesn't matter how hard I go on the throttle it still does the same thing: https://www.youtube.com/watch?v=Z0U848tOw14

 

The only other thing is that two injectors seem to have values that are massively off, though given that the car never hesitates with the MAF unplugged I don't see how this would be causing it: https://i.imgur.com/iwbAlfo.jpg

 

Thanks

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The same device (launch diagnostics) that gave the injector reading can also give live data. If it's available, check the actual charge pressure and the specified charge pressure. You'll see if the turbos producing enough air pressure.

 

If not check the vaccum lines. I think the only way to actually get to them is by removing the intake manifold. Mine were completely collapsed when I changed them.

 

Edit: This is the graph I got for mine when I was checking for boost issues. You'll get something similar. Drive it while it's connected.

 

The injector values don't mean much to me. I don't understand why they're so off. Maybe do a leak off test.

Screenshot_20180922-183025.png

Edited by Qasim

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Thank you for your help, I am just wondering what would happen if I were to unplug the fuel rail pressure sensor on the end of the fuel rail towards the bulkhead? This is just to test and see if this sensor is the culprit. I have tried unplugging the fuel filter pressure sensor but it didn't solve it.

 

No. 8 on this diagram: https://www.realoem.com/bmw/enUS/showparts?id=DP02-EUR-01-2002-E39-BMW-525d&diagId=13_2041

Edited by LifeOfDesire

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3 minutes ago, Qasim said:

Do you have full power after 2500 rpm and will it keep on pulling.

If it can get past 3k RPM then it tends to keep pulling, but quite often when the hesitation gets bad it can't even accelerate hard enough even if I put my foot to the floor.

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14 hours ago, LifeOfDesire said:

If it can get past 3k RPM then it tends to keep pulling, but quite often when the hesitation gets bad it can't even accelerate hard enough even if I put my foot to the floor.

I would start with the vaccum lines, it's a DIY job if you have some mechanical skills. In my own experience, if the cars not driven hard enough, the vanes become clogged.

I ran it with some forte turbo cleaner in the tank and drove it hard, I noticed a vast improvement in acceleration. I just have a boost leak from my intercooler to sort out. Hopefully that will be that taken care of.

 

Edit.

After the vacuum lines, you should see a night and day difference. Then try the cleaner if you want.

Edited by Qasim

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I am replacing the turbo pressure converter and the vacuum lines for it as well this week, will see if that fixes anything. I looked at the charge pressure when it was driving, and when it stuttered, it dropped well below where it should have been, so obviously the turbo is dropping out when it stutters.

 

Given that no such stuttering ever occurs when the MAF is unplugged, it seemed more likely to me that it would be a sensor (or the pressure converter) fault rather than a mechanical fault like a vacuum line splitting. I would have thought that, if there were a mechanical issue as opposed to an electrical one, it would still stutter with the MAF unplugged. Can anyone confirm whether unplugging the MAF forces the turbo pressure converter to use a 'default' or failsafe setting? Obviously unplugging the MAF causes the ECU to use a failsafe mode but I was unsure whether this affected the pressure converter.

Edited by LifeOfDesire

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Here is an update and some pictures of the times that I have managed to catch the stuttering in the data.

 

nb0tMah.pngCyB6CNR.pngq24CXvS.pngiaa5jFm.png

 

I already knew the charge air pressure was dropping well below specified when it stuttered, but I have now noticed that actual air mass is dropping well below specified when it stutters too. I had a new Bosch MAF sensor fitted last year so it shouldn't be that, unless it somehow needs coding. Would that be done in ISTA/P?

 

Edited by LifeOfDesire

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