[RobUK]

Following replacement of a faulty fuel pressure sensor, had problems with the car reporting a drivetrain error and going into limp-home mode which the dealership was having difficulty fixing.

They've now said they've traced the fault which is something they've never seen before. Touch wood the problem hasn't reappeared so far although it's early days. The following may make a bit more sense to the technical guys here - anyone care to translate...?



Overboost? Sounds like more power but in a bad way. Wonder if that could also have been the cause of my smokey exhaust when accelerating?

[NISFAN]

Well, looks as though the wastegate was struggling to control boost pressure.

The pressure watch dog would have tripped 'limp mode'.

As for the smoke, yes it is possible. Many turbo engines are mapped to go over rich when boost gets above prescribed limits.....a sort of self defense mechanism. The extra fuel cools the charge (overboost adds heat), making knock less likely.

Extra rich of course can show as smoke out the exhaust.

[SomeRandomer123]

Originally Posted by NISFAN

Well, looks as though the wastegate was struggling to control boost pressure.

The pressure watch dog would have tripped 'limp mode'.

As for the smoke, yes it is possible. Many turbo engines are mapped to go over rich when boost gets above prescribed limits.....a sort of self defense mechanism. The extra fuel cools the charge (overboost adds heat), making knock less likely.

Extra rich of course can show as smoke out the exhaust.

That all sounds feasible doesn't it! Sounds like limp mode has saved your engine there.

Wow, never heard of a BMW or any modern cars like ours actually having overboost issues!

Thought of an exorcism for you car, Rob?

Let's hope you get a few issue free miles on the clock now!!

[Waitey]

Sounds like the boost control solenoid was sticking. I bet before they bench tested it they sprayed some WD40 in it.

[RobUK]

Originally Posted by NISFAN

Well, looks as though the wastegate was struggling to control boost pressure.

The pressure watch dog would have tripped 'limp mode'.

As for the smoke, yes it is possible. Many turbo engines are mapped to go over rich when boost gets above prescribed limits.....a sort of self defense mechanism. The extra fuel cools the charge (overboost adds heat), making knock less likely.

Extra rich of course can show as smoke out the exhaust.

Thanks that does make a bit more sense that what they wrote. Car seems to be back to its old self, the hesitation in manual mode between 1500-2000 rpm is gone, and the car actually feels a lot smoother and a bit more lively. Haven't driven at night since picking it up to see if the exhaust smoke has gone, although they did say they'd checked it and everything was normal.

Just the other issues to get fixed now!

[RobUK]

Originally Posted by SomeRandomer123

That all sounds feasible doesn't it! Sounds like limp mode has saved your engine there.

Wow, never heard of a BMW or any modern cars like ours actually having overboost issues!

Well I'm hoping there was no damage caused.

Originally Posted by SomeRandomer123

Thought of an exorcism for you car, Rob?

Let's hope you get a few issue free miles on the clock now!!

I'm open to any suggestions - know a good priest?

[PrinceBarin]

Originally Posted by Waitey

Sounds like the boost control solenoid was sticking. I bet before they bench tested it they sprayed some WD40 in it.

I would live to think that, even on the most modern if engines, there is still a role to play for a humble can of WD40