cutting out at high rpm's

[joe hurst]

FYI, 

 

The electronic throttle body motor can become faulty.  This can then cause additional damage to the Engine Control Unit (ECU) throttle body circuit drivers inside the ECU. Guide fault codes logged by engine management system can be P1500/P1523/P1526. If only the ECU is replaced, the same problem can recur, as the real cause is the throttle body motor. This is why it’s advisable to replace the throttle body too.

 

This is on a Vauxhall ECU, but they are exactly the same fly by wire Bosch system, so it's a fair conclusion that the Porsche P1508 code (torque comparison signal implausible)  ''could'' be down to bad code in the DME due to the throttle body going bad and causing voltage spikes that dmage either internal ecu components or code.

 

the fact that a new TB temporarily solved it strongly implies this is the case.

[joe hurst]

OK, definitely solved now!

 

it was indeed the DME..

 

so I will again outline symptoms and codes incase anyone else gets the same issue.

 

car would cut out like hitting the rev limiter at 5800rpm, resloved by keying off and back on again.

 

on graphing of TB and accelerator pedal you see an immediate drop in voltage to both, not gradual just a complete loss of voltage to both the pedal, and the throttle body.

 

changing the TB for a new will seem to resolve it as the ecu goes throught the learning process , it will then re-occur.

 

main re-occurring code was P1508, which means torque monitoring fault, I have spoken to several Porsche specialists and the code would be dealt with by Porsche by replacing the DME.

we have come to the conclusion that the car was run with a faulty throttle body and the jacking motor was creating voltage spikes which damaged The throttle drivers inside the DME coding.

 

This has been tricky on this particular car as some other faults were masking the issue with ''ghost codes'' which has required those issues to be resolved before being able to diagnose and fix the main issue.

 

also when the cut outs occured there was always more than one code present and the car would on throttle off would run very badly , timing all completely lost.

 

If this does happen to your and is resolved by keying off and back on again i would look at the DME first, maybe borrow one from a forum member if possible.

 

its a difficult one to diagnose as each time a part was replaced the DME would go through an adaptation making you think the problem was resolved ( until it returned each time)

 

if your car is otherwise healthy it would be much easier to track down for sure, and of course hindsight is 20/20! 

 

I suppose the upside of this fault is that the car can be driven perfectly below the RPM at which the fault occurs, meaning you have time to sort it, and don't have to get a flatbed and it recovered to a garage.

 

I hope my investigation into it and subsequent solution will help someone else!