Eric_who

I have an 03 C5 Z06 that has a weird intermittent power loss and bogging issue, usually when the engine is cold, and tends to go away when warmed up. I put new plugs and wires, no change. Checked the fuel pressure at the fuel rail during idle and revving, fuel pressure is a constant 55-60psi. Next im going go use my diablosport i3 to do datalogging, but I’ve never done it before. Is there any specific parameters i need to be looking at for a problem like this? Im assuming this problem is being caused by a vacuum leak or unmetered air getting into the engine after the MAF. Thanks for any info

wobblyflopper

I'd pay close attention to your spark advance/retard. If the pcm sees something it cant make sense of it'll pull spark way back which would account for it being intermittent.

wydopnthrtl

If its only a vacuum leak, it would generally be ok when cold and get worse as the engine warms (ECU leaning out the mixture as ECT increases)

C5 Diag

Since it’s acting strange when cold I’d be checking live data for your ECT…if you are able to graph with this tuning software I would also look at TPS and APP sensors…if TPS signal drops momentarily while graphing
the car will bog and hesitate…look at your O2 sensors and fuel trims too…if long term fuel trims are elevated at idle…over 10% but decrease at 3000 RPM it’s a vacuum leak…this is diagnostics 101 !!

tblu92

AGREE a vacuum leak would cause a way Positive LTFT fuel trim----Also you can spray some brake cleaner while idling around the intake manifold /T-Body/ vacuum like to see if the engine either surges or tries to die--Tell tell sign of a leak
Also data log the actual final timing as well as the Front 02 voltage averages-- They should read between .400 and .550 millivolts