TBI BACKFIRE

[Stevemoravsky]

95 chevy g20 5.7L tbi 4L60e
Tbi backfire about half way down on pedal under load only. No backfire at all in P/N at any rpm. No codes. Vacuum good. Compression good. Timing 0° btdc base idle. Advances to 20 btdc with EST.
New distributor. Fuel pressure 12psi at tbi. All sensors appear to be working fine. New wires.
Using 1320ELECTRONICS obd1 scanner. Cat removed. New muffler. No smoke out tail pipe. Not over/underheating. Shell 93 octane. Help?

[95GMC]

With the scanner hooked up are you seeing high integrator/BLM numbers over 128 when the issue happens? Also does the o2 voltage hit about 850-900mV under wide open throttle? Most common cause for backfire through intake is a lean condition. If your o2 voltage drops/stays the same instead of pegging at 850+ mV when you floor it then it's running lean.

[stew86MCSS396]

Is this a unaltered stock engine with no modifications? Just throwing this out, addition of vortec heads to a stock engine and running it on a stock tune can cause the issues you're describing.

[Fast355]

Is this a unaltered stock engine with no modifications? Just throwing this out, addition of vortec heads to a stock engine and running it on a stock tune can cause the issues you're describing.

Definately need more info. I have seen people put the wrong injectors in these as well as try to run them on the wrong memcals. Most 350s in 95 ran BJYL, BJYM, BJYN. The injectors should be 5235206. I have also seen a bad connection to one injector cause an engine to idle and cruise fine but bog or lean pop on acceleration. What does the injector spray look like?