GM 5.7 TBI Misses During Acceleration

[Giacopuzzi]

My patience is wearing thin. I have a 92 K1500 4x4 Z71 Ext Cab, 5-Speed, Crate motor LT1 with less than 20K. Truck has less than 50K. The problem all started when I went to go have a smog check. While running on the dyno toward the end of the test it starts missing under acceleration. So far I've replaced plugs, wires, cap, rotor, distributor, coil, fuel pump (twice), fuel filter, TBI fuel regulator. Completely cleaned out TBI and injectors. It has 140psi on every cylinder. Fuel pressure is at 12lbs. Idles smooth, only under hard acceleration does it miss. Smooth during slow acceleration without load. Solid miss accelerating all RPM ranges under load. It chugs. It's almost a lean miss, cleans up when letting up on accelerator. Any ideas would be appreciated.

 

Thanks!

[Friz]

Looks like you've covered the basics. I'd get the O2 sensors checked. It does sound like it's leaning out. You could check the plugs after a hard acceleration run. See if they look lean. Do a hard accel run then kill the motor. That will give a look at the plugs as you were accelerating.

Be careful, though. With the motor shut off, you have no power steering or brakes.

[Wingnut]

Is it throwing any codes (SES light)?

 

My '92 was doing pretty much the same thing, and it turned out to be the knock sensor (on the block, by the starter).

[Jerther]

would a faulty but working knock sensor throw a SES?

[Wingnut]

Mine only threw the light every once in a while. But would ping under load every time. If I really hammered it, it would come on just about every time.