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LTFT Possible cause?

OldTimer

Member
Joined
21 Aug 2018
Messages
7
Hi All,

Slight concern with my 1998 C2 996.

The Long term fuel trim of bank 2 is fine and remains around 0% but Bank 1 is around +4% at idle but increases with revs and load to around +11% at cruise.
If it was a vacuum or exhaust leak I would imagine this would be worse at idle but its not and If it was fuel pressure i assume it would impact both banks?

I've put in a bottle of Injector cleaner but too early to tell if its made any difference but are there other common 996 issues that may cause this problem ?.
Asking as I'm about to do a 500mile motorway trip and don't want to think its running lean....
 
Do you actually have a fault .. ie .. hesitation , misfire eml light etc ?

Have you just bought a code reader and are now wondering if the car actually has a fault because you are looking at values ?

A single bank fault on the early cars would lead me down the route of camshaft adjustment .. the slippers can wear .

For a complete bank to be at fault then you either need to have a single cyl causing a large issue or a problem which affects all of them .. To me both of which would have a driving fault .

Also a single value like long term fuel trim is not enough to diagnose a fault .. start looking at lambda sensor switching .. compare bank to bank ..

Prove there is a fault and it's not just an adaption the car is making to keep everything running correctly .
 
Faulty variocam solenoid on one bank :dont know:

My fuel trims where out to each other due to this.
 
Hmm..ok had not considered the variocam

No specific fault or codes (at least what my reader can see).

Only issue has always been a slightly lumpy idle - I'd changed the engine mounts partly hoping to resolve this. Also seems a bit flat low-down but I've nothing to compare against

So yes may be paranoia but the OCD element in me expects to see closer LTFT Values

In terms to the Lambda switching what should I expect to see?

Thanks
 
That deffo sounds like faulty variocam - lumpy idle and flat at lower revs. The solenoid can be stuck in the advanced position so it runs fine at high revs but less torque at lower revs and also lumpy.

You can engage/disengage them whilst the car is ticking over using a proper Porsche diagnostic tool (PIWIS, etc.)
 
Thx all - looks like something my indi will need to take a look at. Even just changing the solenoid (if it was that) does not look that easy on these early models :eek:
 
No its not.
 
Correct. Then lock cams down, remove rocker cover, strip down solenoid assembly then all back together.
 

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