Hey all,

I am embarrased to be posting on a problem since I am a shop that specializes in GM EFI performance but I am stumped and will give up a bit of pride for any helpful suggestions.

I just finished up an engine rebuild for a customer, threw in a big cam,ported heads, and all the usual items to make a 420RWHP N/A set up.

I fired the car up off a base tune and pulled it over to the dyno side of the shop. All was as expected, had the idle and part throttle nailed down from running the same combo a few times before.

As I was warming the car up on the dyno it seemed to pull good at part throttle but would bog down a bit on shifts. A/F was looking good and the logs showed nothing unusual. I put it back in neutral and reved to four grand with no problem. I then reved again, backed off, then hit it again before the rpms dropped much and the thing bogged harshly and let a back fire like nothing else out.

The problem was repeatable and the A/F never flinched while bogging. I have checked all the usual suspects so the common sugestions while appreciated are not going to help. Plugs changed, wires changed, opti changed twice, coil,Ecm, MAF, all change to no effect. Wire routing checked twenty times, all grounds tested, turned lights out in shop looking for arching, valves re-lashed a couple times, not comp R lifters. I have changed programs, and ran a file that worked flawless on the same combo from a past car.

I appreciate any help that you guys can throw out there, I just don't see where to go next.

Thanks,

Martin

 

more info would be a start. Year, suporting mods, ect.

Did you run a fuel pressure load test? Sweep the TPS? ect

 

Check your fuel pressure.

 

I have checked the fuel pressure a few times and it holds steady under load. One thing I have not changed yet is the TPS. It checks out fine when sweeping but I looked a little further into it on the logs today and it seems to be acting weird. it looks like the TPS postion is dropping down to zero in spots were the rpms are elevating or maintaining.

It is the TPS from the stock car installed on a Holley 58mm T-body. As for the mods it a 95 camaro, gm847, ported 2.02 heads, rockers,long tubes, 42# injectors, complete emissions AIR and EGR delete.

Thanks for the suggestions, I will dig up a TPS and give it a shot.

Martin

 

You might want to verify that the coolant temp sensor for the PCM is functioning properly.