Discussion
Hi, I've had my 996 (2002) for over a year and had no previous issues but it has developed a problem tonight. The car starts and drives OK but won't rev past 4000 rpm and when it reaches this level the engine pulses as though it was hitting a hard rev limit. There are no warning lights on the dash or any other symptoms that I can see or hear. My only thought was coil packs but my search didn't find any other 996 problems like this.
Anyone had this before?
Cheers
IR
Anyone had this before?
Cheers
IR
Not in either of my Porsches and not that I can remember in any other car, but I won't let that stop me...
Probably not coil packs. I would expect you to report a CEL if the coil packs were acting up.
Reads more like a fuel supply problem or perhaps some blockage of the engine air intake system.
Do you know the car's service history well enough to have confidence the fuel filter has been changed recently?
Are you sure the car has not suffered from an invasion of mice that might have built a nest in the intake system?
Longer shot but any chance of stale (and I mean stale) gasoline in the fuel tank?
Does the engine otherwise run ok? How's the idle speed? If it hunts there's always the AOS to worry about.
Probably not coil packs. I would expect you to report a CEL if the coil packs were acting up.
Reads more like a fuel supply problem or perhaps some blockage of the engine air intake system.
Do you know the car's service history well enough to have confidence the fuel filter has been changed recently?
Are you sure the car has not suffered from an invasion of mice that might have built a nest in the intake system?
Longer shot but any chance of stale (and I mean stale) gasoline in the fuel tank?
Does the engine otherwise run ok? How's the idle speed? If it hunts there's always the AOS to worry about.
Thanks for the feedback.
The car has had 2 services and covered 7k miles in the last year, 3k in May during a Euro road trip and it has performed faultlessly. Even managed a good lap at the ring. It ticks over and drives just as expected but there is nothing I can do to get it to exceed 4k revs! It's definitely feels like an intervention not a air or fuel issue as it feels fine until exactly the same point in the rev range each time.
Is there a default setting that the ecu selects if it detects an electronic issue??
IR
The car has had 2 services and covered 7k miles in the last year, 3k in May during a Euro road trip and it has performed faultlessly. Even managed a good lap at the ring. It ticks over and drives just as expected but there is nothing I can do to get it to exceed 4k revs! It's definitely feels like an intervention not a air or fuel issue as it feels fine until exactly the same point in the rev range each time.
Is there a default setting that the ecu selects if it detects an electronic issue??
IR
Fickle1 said:
Thanks for the feedback.
The car has had 2 services and covered 7k miles in the last year, 3k in May during a Euro road trip and it has performed faultlessly. Even managed a good lap at the ring. It ticks over and drives just as expected but there is nothing I can do to get it to exceed 4k revs! It's definitely feels like an intervention not a air or fuel issue as it feels fine until exactly the same point in the rev range each time.
Is there a default setting that the ecu selects if it detects an electronic issue??
IR
There is a limp mode that is triggered under certain circumstances. These include a problem with the e-Gas system, the Tip, and possibly some critical engine sensor being bad or a sensor reading being off the scale. I forget now.The car has had 2 services and covered 7k miles in the last year, 3k in May during a Euro road trip and it has performed faultlessly. Even managed a good lap at the ring. It ticks over and drives just as expected but there is nothing I can do to get it to exceed 4k revs! It's definitely feels like an intervention not a air or fuel issue as it feels fine until exactly the same point in the rev range each time.
Is there a default setting that the ecu selects if it detects an electronic issue??
IR
However, if the ECU/DME enters limp mode I think this is signaled by the CEL coming on and one or more error codes.
Besides, what I recall reading about limp mode 4K is is way higher than what max RPMs in limp mode would be.
But I can't can't say for sure so you are looking at taking the car to a qualified shop for a professional tech's diagnosis and opinion. He can query for limp mode active and if it is active can probably query for the error codes that triggered limp mode.
cd1957 has a good suggestion if you want to try to diagnose this yourself. Disconnect the MAF at the wiring harness connection then clear the DTCs to reset all the fuel adaptation values back to their defaults. You'll need an OBD2 code reader/data viewer for this unless you want to disconnect the battery. My advice would be to get an OBD2 code reader. I prefer using the OBD2 code reader as playing around with the battery cables is a good way to zap the DME.
Then start and drive the car normally and observe is the same behavior is present. If it is it (probably) ain't the MAF. If it is not present, then reconnect the MAF, clear the DTCs again, and go for another test drive. This time you want the behavior to come back.
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