996 c4s - 2003, tiptronic - error codes - CEL - loss of power

[jdredgers]

Hello - I hope someone will be able to give me some advice.
I have 2003 C4s - 80,000 miles. It has been regularly serviced by Main Dealer, and since by Indy. No real issues until just after last service (coincidence??).
Basically the car still drives and performs well until you use hard acceleration. By this I mean normal driving, hitting around 4300 RPM changes the gear up, and all goes well.
However under Hard Acceleration whereby revving goes to around 6000 RPM before change up, a variable problem has arisen.
Sometimes the CEL comes, mostly it does not.
Sometimes, the CEL comes on, and stays on. Sometimes it goes off again.
Sometimes it comes on, stays on, and in the morning it is off again.
When the indy reads the codes when the CEL is on we get P0336 and p1266
When the CEL has been on, and goes off again, there are no codes stalled.
The behaviour of the car at the point the CEL comes on is interesting. It feels like you hit a rev limiter. The RPM need stops, and feels like no fuel is coming through. If i back off, then normal driving resumes. If i dont back off then the CEL is tripped and a loss of power to limp home mode is enabled. This is cured by turning off and on again. The CEL remains, and driving is still fine. Taking it back up to hard acceleration was fine with no issues or misfires or rev limitation, In every other way the drive is sound (low revs, town driving, normal motorways) no misfires.
So over a period of 8 weeks we have:
replaced coils and plugs
replaced crankshaft position sensor
replaced throttle position sensor
had service and oil change.
So now the ideas being presented to me:
1. Variocam Solenoid Actuators (engine out job)
2. Not really sure.
3. All wiring harness to be replaced.
4. P1266 being reported occaisionally by people driving at altitude - i was not...only 100m above sea level!
I would be pleased to hear any thoughts/ideas/suggestions.
Many thanks
Jason
ps - first time asking! - be gentle.

 

[Richard_Hamilton]

Jason!!

Sorry to hear of your woes. What you describe doesn't sound like a common or simple (to diagnose) fault. This is what the diagnostic manual says for those two fault codes;


P0336
Crankshaft Position Sensor, Signal Implausible

Diagnosis conditions
"¢ Engine running

Possible fault cause
♦ Corrosion in the connector
♦ Loose contact


P1266
Fuel shutoff function monitor - signal implausible

Diagnosis conditions
"¢ Engine speed > 1,120 rpm

Possible fault cause
♦ DME control module faulty

I wouldn't have thought it was a Variocam problem, as it would throw up timing and Variocam specific codes.

If you would like copies of the diagnostic sheets, drop me an email and I'll attach them to a reply.

 

[jdredgers]

Hello Richard,
Many thanks for your reply. It does seem to be an usual set of things. After reading as much as possible it seemed a posting was the only way to learn more, and to give me a little confidence that i really should not be looking to pay for a variocam checkover just yet! they were talking around 2-3k of work for that! - the fact there are no variocam faults is now considered a plus!
Therefore it would seem an electrical fault - or as pointed out a DME fault.
I will drop you an email to get those diagnostic sheets you mentioned.
Again, thank you - sometimes some reassurance is quite welcome from a 3rd party!
Thanks
Jason

 

[tag10]

Problem gear changes during hard Acceleration maybe caused or initiated by tiptronic oil level.
During the service have you changed the ATF oil or had it checked.
This maybe a long shot and not related.

Tag10 (2003 996 targa tiptronic)

 

[jdredgers]

Hi thanks for the reply - it was an initial thought, but on working through it the problem is not happening at gear changes, it is happening when you have a kickdown change, and then keep the acceleration and the revs head up above 4300.
So when in 5th, cruising, then kickdown to 3rd, hard acceleration, the revs up to 5-6,000 and change to 4th, then as revs building in 5th it happens at 4,300 or so.
I will have to go and trigger it again so i can really record what happens!
Thanks again - all ideas appreciated.
Jason

 

[jdredgers]

Hello to All again,
Just a small update.........
When driving normally in automatic mode, all is fine under normal acceleration. ie when you hit around 4200 RPM the gear shift happens. - Smooth.
When you accelerate hard, ie try to rev past the 4200 RPM then (and whether using manual changes or full auto) then around 4300-4500 RPM it is like the engine hits a flat spot, the rev waver a little and the car slows a little. Then starts to pick up again, with the RPM progression not as smooth.
Previously this set off the CEL; now it does not.
Any further suggestions please?
Thanks
Jason