Poor electrical connection, open or short in circuit, defective esc module, defective knock sensor, defective ECM.

That's what the book says. I've replaced the following or tested,

Tps
Iac
Ecs
ECM
Distributer
Plugs
Wires
Maf burn off relay
Knock sensor
Egr valve
Egr solenoid switch
All fuel injectors
Rebuilt fuel pressure regulator
Distributed cap and rotor
Coil

I'm probably forgetting something but that's what I remember right now. This car used to be a v-6 car with auto trans and one ledger rear end. It is a 1990 firebird. It now contains a 5.0 bored out to 5.7, t-56 and posi rear end. Wiring harness came out of an1987 firebird and engine came out 87 iroc. Trans and rear end are out of 1994 formula. I've got everything working except speedo and this ghost I'm chasing through the engine compartment. Car runs great until you go into 5th on the way up through the gears then it feels like it loses power and when you let off the throttle, there's the good ol check engine light. Code 43. Any ideas? I'm fresh out.

 

But did you work through the code 43 fault chart completely to narrow the problem down ?
See
http://www.chevythunder.com/maf_esc_module_code_43.htm

 

Vetteoz, thanks for the flow chart. I'll be checking that a little later today.

 

POSSIBLE EGR COMING ON?
5TH GEAR ONLY RIGHT?

 

Ever figure it out?