[johnw7884]

My 996 3.4 is running extremely lean on higher revs. Tested on dyno, got only 120 to 140bhp. Engine starts to run a bit lean from about 3000rpm, and only revs to about 4300rpm under load, when it is running so lean it will not take any more revs.

When driving in traffic, engine feels very responsive. But when I floor it, it runs strong until 3000rpm, and gets worse the higher the revs. At 4300rpm runs completely out of power. On idle, revs very well until rev limiter.

So far I have figured out;
- No fault codes (at least does not show on Bosch tester)
- Fuel pressure stays constant, on full throttle stays at about 3.8 bar

I tried to run the MAF disconnected; it idles a bit erratic, but on full throttle same 140 bhp at 4300rpm.

Any ideas? I have tried to google for typical DME input/output values, but have not found any. I have thought maybe the variocam is not working properly, but how would I go about testing them?

I have also considered resonance flapper, MAF, O2 sensors as possible causes, but I do not know how to test them. Also I am puzzled that there are no fault codes.

Any help appreciated. Many thanks!