I have an '81 C10 that I just finished swapping an L33 5.3 into. I've been driving the truck a few weeks now trying to work all out all the bugs and making an everyday driver out of it. Truck runs awesome going down the road but stutters at takeoff. Less than half throttle is fine but anything more, it stumbles and seems to be misfiring. I've had a buddy watch misfire data while I drive but can't see a problem. If I'm running 50-60 mpg and just hammer down, it shifts down and takes off without issue. Seems to be narrowed down to just takeoff/low speed acceleration. I was told by my tuning guy that the issue is on my end and that all is well with the tune and he can't figure it out. I've also been told that it could be misfiring due to bad grounds, but I've checked every single one. Does this sound familiar to anyone?

Ps - fuel pressure is constant 58-60 psi at all times

 

posting in the correct forum.....

 

If it was bad grounds it would be all the time.

I'd look into the TPS or MAF to see if anything's weird.

 

Replace all the spark plugs. Sometimes they crack and cause a sputtering/missing under acceleration, but it's not noticed at idle or at speed. This can happen after a recent swap with all the header fitting, etc.

I had this issue, pulled all my plugs, and saw no visible cracks, but this was still the problem. Fresh plugs fixed my issue completely.

 

Any codes? Maybe a coil pack or maf sensor.