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OldTimer
Newbie


Joined: 21 Aug 2018
Posts: 5



PostPosted: Mon Sep 09, 2019 2:27 pm    Post subject: LTFT Possible cause? Reply with quote

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....
 
  
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7176
Location: Brighton


PostPosted: Mon Sep 09, 2019 7:02 pm    Post subject: Reply with quote

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 .
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16681
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Mon Sep 09, 2019 7:09 pm    Post subject: Reply with quote

Faulty variocam solenoid on one bank Dont know

My fuel trims where out to each other due to this.
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2000 Manual 996 C4 Arctic Silver Convertible


 
  
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OldTimer
Newbie


Joined: 21 Aug 2018
Posts: 5



PostPosted: Mon Sep 09, 2019 8:35 pm    Post subject: Reply with quote

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
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16681
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Mon Sep 09, 2019 9:24 pm    Post subject: Reply with quote

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.)
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OldTimer
Newbie


Joined: 21 Aug 2018
Posts: 5



PostPosted: Wed Sep 11, 2019 10:06 am    Post subject: Reply with quote

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 Surprised
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16681
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Wed Sep 11, 2019 10:17 am    Post subject: Reply with quote

No its not.
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Dammit
Indianapolis


Joined: 23 Sep 2016
Posts: 2275



PostPosted: Wed Sep 11, 2019 10:26 am    Post subject: Reply with quote

IIRC you need to take the manifold off?
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My 996, AKA Project Ridiculous
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16681
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Wed Sep 11, 2019 10:32 am    Post subject: Reply with quote

Correct. Then lock cams down, remove rocker cover, strip down solenoid assembly then all back together.
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