Intake Backfire

[Albrainya]

Heres my setup:
92 5.0 stock bottom end/rebuilt
thumper heads (ported e7's)
b-303 motorsport cam
1.7 roller rockers
gear drive advanced 2 degrees (cam was degreed)
efi spyder intake
24# injectors
76mm c&l mass air
t-5 5 speed
8.8 rear with 4:10s

I get a single backfire in the intake on hard accel, cold or hot, then the car takes off. any suggestions - my FP is set to 40 psi, timing with spout out is set at 12 degrees.
pass codes from computer.

 

[jrichker]

Backfiring is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, misconnected. Check the line for the vapor recirculation system – it is easy to nock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen. Check the mass air flow electrical connection and see that it is tight, the same goes for the fuel injection wiring harness connectors up on top of the manifold near the firewall.

 

[troyGT03]

jrichker is on the ball. lean condition, timing, or the main culprit- vacuum leak

 

[Albrainya]

set the base timing to 16 degrees and the intake backfire is gone and the car pulls like a raped ape, no pinging either.