I recenty finished an ls1 t56 swap in my 85 iroc, it has been running amazing for the past month up until last week, in high rpm under a load the car bucks...bad, as if it were a pissed off bull, it feels like the ignition is being shut off and turned on rapidly, not really a missfire. It doesnt do it every time either only 1 out of 3 WOT pulls and not in any specific gear. The engine is rebuilt, has a new aeromotive 340lph pump, everything has about 1200 miles on it. I have a fuel pressure gauge in the car and when it starts bucking it doesnt seem to drop enough to cause the issue in my opinion, its only losing 1 or 2 psi when the vaccume eases up on the regulator. Every sensor on the engine is new, im not sure where to start with this, any help would be greatly appreciated......i have searched through forums there are similar issues out there but i cant seem to find a confirmed fix on any of them

 

Hmmm. Based on a somewhat-similar experience I had several years ago, my first inclination would be to start looking at the wiring. In my case, there was a two-wire harness that went to the coil that (apparently) had flexed repeatedly until the wires were nearly broken clear through. You couldn't see anything wrong, & since the problem only happened intermittently, it was a bit of a B!TCH to track down (although that was at least partially made up for by how easy it was to fix when I found it).

I would suggest lettng the engine run in your driveway & grabbing different sections of the wiring harness (I'd probably start with each of the coil harnesses) & just wiggling that part of the harness a bit, just to see if that has any effect on how the engine runs. Of course it could also be something like the TPS, MAF sensor, etc., do don't get too focused in on just one thing... Finally, if you don't have your harness tied down to the engine/bodywork to minimize flexing, this would be a good time to address that, just to stave off potential future problems. Good luck!!

 

Also, the FIRST question that should be asked - have you pulled any codes yet?? That can dramatically shorten the time it takes to track something like this down!

 

 

Yea, i have a code scanner and i check for codes almost every time im in the car it always has nothing

 

I dont have any tuning software, i do have access to a snapon scanner at my job it doesnt save the data tho it just does live data, hard to keep track of it while doing 100+mph and i have no brave soles willing to take a ride with me to watch the scanner