Poor Acceleration / Stalling under Load
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Junior Member
Joined: Dec 2023
Posts: 36
Likes: 3
From: Wilmington, NC
Car: Pontiac Firebird 91’
Engine: 305 TBI
Poor Acceleration / Stalling under Load
Hey guys,
I’m having a heck of a time trying to diagnose what is going on with my 1991 5.0 TBI Firebird Base Model.
When accelerating under any load the car seems to not fire properly or maybe it’s bogging (I’m not sure) but it accelerates fine in Park and Neutral. It is almost the same feeling as if you were driving a stick shift, and you were in too high of gear for the lower speed you were going - it just seems to not get any acceleration / power.
If you press and hold the accelerator for too long, it will keep bogging or whatever it is doing, and it will eventually stall out.
The only code I am getting is GM 12.
I have replaced the following to try and remedy this problem but none have seemed to work.
Rebuilt and cleaned entire TBI
New AC Delco fuel injectors
MAF Sensor
Throttle Position Sensor
IAC valve
EGR Valve
EGR Solenoid
Inner Air Temp sensor (air charge)
Engine Temp Sensor
Fan Switch
02 sensor
thermostat
Distributor
Spark plugs and wires
All New fuel lines, fuel filter and upgraded pump.
I have replaced all vacuum lines hooked to TBI and EGR
Installed new fuel line with an external regulator that regulates pressure at 13-14 psi (even under load) I’m getting plenty of fuel. I Platted off the internal fuel regulator (it was doing this problem before I messed with the fuel regulator)
The only solenoid I haven’t replaced is the charcoal purge canister.
What in the world am I missing here?
Someone mentioned the torque converter… why would this affect acceleration under load?
Any help would be much appreciated,
I’m having a heck of a time trying to diagnose what is going on with my 1991 5.0 TBI Firebird Base Model.
When accelerating under any load the car seems to not fire properly or maybe it’s bogging (I’m not sure) but it accelerates fine in Park and Neutral. It is almost the same feeling as if you were driving a stick shift, and you were in too high of gear for the lower speed you were going - it just seems to not get any acceleration / power.
If you press and hold the accelerator for too long, it will keep bogging or whatever it is doing, and it will eventually stall out.
The only code I am getting is GM 12.
I have replaced the following to try and remedy this problem but none have seemed to work.
Rebuilt and cleaned entire TBI
New AC Delco fuel injectors
MAF Sensor
Throttle Position Sensor
IAC valve
EGR Valve
EGR Solenoid
Inner Air Temp sensor (air charge)
Engine Temp Sensor
Fan Switch
02 sensor
thermostat
Distributor
Spark plugs and wires
All New fuel lines, fuel filter and upgraded pump.
I have replaced all vacuum lines hooked to TBI and EGR
Installed new fuel line with an external regulator that regulates pressure at 13-14 psi (even under load) I’m getting plenty of fuel. I Platted off the internal fuel regulator (it was doing this problem before I messed with the fuel regulator)
The only solenoid I haven’t replaced is the charcoal purge canister.
What in the world am I missing here?
Someone mentioned the torque converter… why would this affect acceleration under load?
Any help would be much appreciated,
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