Hey all,
Thought I'd post here since I'm betting someone messes with tuning new performance cars.
I bought a 06 GTO from a wrecker yard. Got it back on the road and figured I'd try a used diablosport predator I had lying around on it. I knew the car had headers and aftermarket heads on it, so I thought maybe the predator would work better than the stock program until I could tune it properly. Well, the idle was much more smooth and the low rpm throttle was smoother too, but once the car got to 3rd gear and about 3000 rpm it just fell completely flat. Acted the same way in 4th at the same speed and lower rpm. Like a rev limiter on a 4 wheeler. I didn't hear any knock and no engine codes came up (traveled about 1/2-3/4 mile). As soon as I was back in my driveway in 2nd gear it ran smooth again (though I didn't test it by revving back up).

Curious if anybody has any insight as to what was going on? I have since learned that the car has a larger cam in it as well. I thought perhaps the diablo tune wasn't compensating for all the increased air intake and as the rpm's built up this caused the mixture to become lean enough that the ecm cut back the timing/fueling system somehow?

Any thoughts?

(The car is tuned now and I'm not using the diablo. I just want to understand what was going on.)

 

It might have had too much timing causing spark knock or just the cam causing the knock sensors to go crazy to pull out a ton of timing which will make the car feel like a dog.

Tobin

 

Does the computer have a speed limiter built in?
could be the transmission isn't locking up properly and kicking the computer into limp mode

 

valet switch?
fuel preasure low?
Does it do it with out the tuner?