Lt1 guys going lean, then backfires under load

[Sleeper]

Working on a swap car, oh what fun. 95 caprice lt1 in a elcamino.

I just messed with it a little. I cleaned the maff, has new plugs, wires, not sure on the opti. It runs fine when cold, but once you reach closed loop it will stutter and miss and eventually backfire under a load.

Im waiting on a cable to use with freescan. I've got a bluepoint microscanner, but it will not read. The car is a 95 with the obd1 computer, but the 16pin obd2 connector.

Any lt1 guys out there?

Fuel pressure is 39-40 at idle. I cant take it down the road and see as my line isnt long enuf.

[DC COBRA]

The 95-96 lt1 uses some different fuel pump varying the 8th digit of the vin#. Ran into the same problem when I replaces a pump in customers car, part store guy gave me the first delphi pump it listed, man that was a headache to figure out. Some pumps pumped 40 lbs some pumped 50plus. I got the 40 originally then tried the 50 fixed the problem same as your having. Part number for delphi wa FE0111.

DON

[Sleeper]

It has been running fine for a while. We dont know the vin because of the swap. Its all a guess. On the caprice forums the fp is within range.

Found out the car as a aftermarket 125lph pump.

[mustang_revival]

My 94 LT1 had similar behaviour when the Opti spark went out. There have been a few opti spark threads on here. I think you can pull it and have it tested.

[Sleeper]

I have a data log if anyone wants to take a look.