I seem to have a stumble at higher RPMS. The car doesn’t really miss, but it’s more of a “stumble” and the car falls on it’s face. The best time I ran today was 12.9 @ 107mph with this problem. The first two runs, the car didn’t seem to have a problem at all. After that, it seemed to have problems in the higher rpms. The last run, I noticed that it seemed to run great all the way through first, shift to second and then start stumbling or falling flat. If I let off the gas a bit, it would clear right up, until it got up in the higher RPMS again. This happened earlier during the summer and I thought the car was getting heat soaked due to it being 85 degrees out when I was last at the track. Today, it was about 60 and it was still doing it.. On the way home, I did a couple WOT blasts from a stop and not a problem whatsoever. The car earlier this summer did act up a few times on the street at higher RPMS like this, but it went away. I have noticed this problem from anywhere at 4000 rpm on up. I’m sorry if my post is hard to understand.

These parts have about 3k on them, as I installed them last winter with the engine rebuild.
Brand new GM opti
AC Delco Platinum Plugs gapped at factory spec.
Taylor plug wires


These are not new.
ACCEL coil that I installed in 2004
Original ignition module
Original fuel pump
Original fuel injectors

Suggestions on where to start? First, I was going to hook up a fuel pressure gauge to see if my fuel pump isn’t keeping up.


Rob

 

If its really not a misfire, have you considered the possibility of knock retard? That can make it drop power as the timing is retarded.

 

I never thought about that, but I think it's more of a stumble/breaking up. It's kind of hard to explain. One thing I forgot to add, I replaced the MAF with an autozone one back in 2005, not sure if that would have anything to do with it, but I have had nothing but problems with autozones electrical stuff.

 

I have this problem as well. Would love to know the reasoning, a quick search shows many many lt1 owners having this problem. With no answers.

 

Did you scan it at all during these runs? Mine did that last year when my injectors were too small. They would max out at 4500 RPM. Bigger injectors this year and the car pulls all the way through now. Also, could be your fuel filter.

 

Nope, I didn't scan it during the runs.

Found out the problem though, the fuel pump is failing.