I'll floor it to 5k in 2nd gear then just left off and let the car de-accelerate in 2nd gear.. While it starts to de-accelerate, it backfires a little. Is this a sign of being too rich...or being too lean???

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91 Formula
305 TPI 5speed
1LE/G92/WS6

Paxton SN92 polished kit, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL (5200rpm limit),Holley 9mm wires,Ac delco R43ts plugs,stock chip,Ford SVO 24# injectors,Bosch O2sensor,SLP 1 5/8" headers,SLP catback,shortened shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.

 

Maybe just time for a new muffler. Check for other holes/leaks in the exhaust system as well.

I don't think it's a mixture problem.

 

My whole exhaust sytem including headers is stainless steel.
I don't have any leaks by the way

 

TF,

Lean backfire is common in hot engines at higher RPM. Usually this occurs when the throttle is open, not closed. If you are experiencing afterfire (popping in the exhaust) that is a different situation. That is generally from a rich mixture in a hot exhaust system. Every time enough oxygen enters the exhaust stream, the fuel mixture "pops" again. If you lett off the throttle a little more slowly, you shouldn't experience this.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

 

very good point Vader. I remember now it only happens when I rev up the engine quickly, not when I actually am moving.