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Car is a 996 GT3, with a 3.6l motor made into a 3.8l with Porsche 3.8 con rods, P&C's, Cup car exhaust Dyno is a Dynapak with up-to-date SW
Recent rebuild with everything replaced that was bad, Fuel pump is new, injectors are new, plugs, etc.
The ECU is *supposed* to have a Softtronics image, BUT for some reason when the motor could run to 8400 (Softronics moved the redline up a bit), it now seems to be back to the 8200 redline. Thjere were no codes other than the missing O2 sensors as I installed sensors to measure the A/F numbers.
Fuel is 93 octane + Torco additive, temperature ~ 70degF
I have NOT replaced the MAF...
What is disturbing are the A/F numbers. 3 pulls, 3 very different numbers, and in the top case, the motor is just dumping fuel...
Any thoughts, insights? How can a tune or a redline change go away?
Thanks, but solid mounts, knock sensors are not being triggered - checked. It is not a timing thing, but a fuel thing and the curious fact that my redline has dropped...
Do you have a smoke tester? I can’t speak to the lowered redline but every time I’ve had wonky Afr’s or poor running conditions it is almost always a vacuum leak. And they can be so obscure and difficult to find, a smoke machine is almost the only way to find them. Good luck. Sorry you’re having this issue. Also, a new MAF would not be a bad idea just to rule that out. When I had my 996 turbo I used a very respectable tuner who would not turn my car without a fresh MAF given their propensity to slowly go bad even before they throw a check engine light.
Good idea, I don't have a smoke tester, but I can check for vacuum leaks, issue here is that some of these lines are almost impossible to see with the motor in the car
FPR replaced recently? In the days of tuning Mitsu’s/Subies, O2, FPR, Maf where the first culprits. After that, injector cycles, the various sensors (knock, cam, etc).
Separate runs could fluctuate the intake temps. Correction for that will be taken into account.
Good idea, I don't have a smoke tester, but I can check for vacuum leaks, issue here is that some of these lines are almost impossible to see with the motor in the car
Unmetered air usually causes lean conditions. As for the tune, you’d have to hook it up and see the checksums and various bits. I’m sure you’re in that process already.
Vacuum pump. You might only need to drop part way to gain clearance like you would in replacing mounts.
There is a difference between setting a knock sensor induced code and simply triggering the motor to pull timing as designed..
From what I can tell the car has to get seriously out of tune to code a knock problem but I don't have a GT..
I could picture a multi part problem where maybe a vacuum leak and the hard mounts play against each other..
Yep, my go-to for weird problems is electrical. I had a loose - very loose, motor to chassis ground. Tightened that up and my redline re-appeared. I will also check a few other things, but I spent time looking at all the various misfire, roughness, cam timing stuff today and it was all good.
I had not finished my nut & bolt since I re-installed the motor...
I will nut & bolt, check the tune, and then reschedule more dyno time.
That's awesome. With the few italians I have owned, its crazy how many times a running issue can be traced back to a bad/failing/loose ground. Glad you are making progress!
I don't really believe any of this, or that it applies to these motors.
From what I understand the M96 engine is much more sensitive to this than the mezger units, so don't believe that would be an issue. I'm sure Jake could shed some light. My guess is this is software related.
Yep, my go-to for weird problems is electrical. I had a loose - very loose, motor to chassis ground. Tightened that up and my redline re-appeared. I will also check a few other things, but I spent time looking at all the various misfire, roughness, cam timing stuff today and it was all good.
Ray
Although I just re-flashed the ECU, pretty sure the problem was a bad ground, which I guess is a software problem...
WRT Motor mounts, I have been running solid mounts forever, don't have a knock problem. I know that folks keep bringing this up, but does not seem to be the case for the Metzger motors.
07-11-2021, 02:27 AM
So, I hd my car Dyno'ed and now have questions...
