Miss fire with more than 1/4 tank fuel

[Pommy]

Picked up a 2003 cayenne turbo the other day. Test drove with no unexpected issues, obviously with very little fuel. Bought the car and went to fill it up, as soon as I did it started misfiring. 

 

With just under half half a tank it was significantly better, only misfiring every now and then. Below a quarter not a problem.

 

i have an idea of what could be wrong but want to get opinions before I continue solving the issue.

 

no warning lights

 

Any help appreciated

[Loren]

 

If you have a misfire then you have at least pending fault codes. Best to have a look using Durametric or another Porsche specific scanner.

Early Cayenne's did have problems with ignition coils (several design changes since new) and fuel pump failures.

[Pommy]

Ignition coils recently changed. Pumps changed 3 years ago and apparently tested recently. 

[Loren]

That's why you need to have the car scanned for faults. The scanner will identify the fault area.

[Pommy]

Sorry for the ignorance, will a normal ob2 scanner pick up faults? Or does it need to be a Porsche specific scanner?

 

Much more use to older cars without scanners!!!

 

[wizard]

If you do a search on here for 'stutter and hesitation if fuel level above 1/4 tank!' that   documents an epic! 

 

LewisWeller's March 27 2017 post (page 6) may be worthwhile looking at.

 

However, fault codes at the outset should prove invaluable.

Edited August 18, 2018 by wizard

[Pommy]

Plugged it in to new diagnosis machine. Stored codes confirm my suspicion it is the breather valve. New part ordered. 

[Pommy]

Thanks for the suggestions though!!!

[Pxwguad]

Pommy,

 

Could you please be more specific, I'm having a similar issue, what breather valve, part # ect...

Thanks in Advance.