I have a fairly modified 91 305 tbi, 700r4 Firebird Formula with 54,500 original miles on it. I bought it new and did most of the mods myself. Haven't done any mods in the last couple of years.
Problem -
When I frist start my car and drive it, driveability is normal, but after about 5 minutes, when I stop at the same stop sign down the road and then begin to accelerate, the car will miss and on occation stop running. At other times, again after about about 5 minutes and only on acceleration, the car will miss and sometimes backfire through the exhaust. If the car stops, I can restart it immeaditely and it runs normally for as long as I drive it. Likewise, if the car misses/backfires for a couple of minutes, it then drives normally for as long as I drive it. I have not been able to capture the problem with my XP240 scanner. I have tried to find the sloution in the Firebird service manual, but to no avail. I wonder if the problem could have something to do when the car goes from open loop to closed loop, but why does the problem go away after a couple of minutes?
Has anyone experienced a problem similar to this?

Thanks for any help,
Don Moore

 

it would help to know your mods

 

These are my mods-


1991 Pontiac Firebird Formula 305 TBI
Purchased 7-16-90.
54396 original miles (10-15-03).
Synthetic oils and grease.

Modifications -

Edelbrock TBI Performer intake.
TBI modified by Turbo City to flow 565 CFM.
TBI bonnet 1-inch spacer.
Auto Meter air/fuel ratio monitor.
Crane roller tip/needle bearing fulcrum Gold Race Rockers.
SLP cam - Dur. @ 0.050 0.209/0.214, Lift 0.471/0.490, 112° CL.
K&N air filter.
Bosch platinum plugs.
Accel 8mm spark plug wires.
SLP Tri-Y 1 5/8th-inch headers MCCI coated inside and out.
Flowmaster two chamber cross flow muffler.
Custom 3” Cat-Back exhaust system.
Random Technology 3-inch catalytic converter.
Auburn posi.
Richmond 4.10 gears.
TA Performance Products rear end cover.
Dacco 2500 stall torque converter.
Hayden transmission oil cooler.
Darrel Young 700R4 TV Valve 0.521.
Fairbanks 2-4 Billet Servo (700R4)
B&M megashifter.
Paxton supercharger.
Adjustable fuel pressure regulator-external to TBI.
Corvette fuel pump-inside tank.
Vacuum-Boost & Fuel Pressure gauges-mounted inside car (isolator mounted on firewall).
ADS custom chip (primary), Hypertech Thermomaster (secondary).
160° thermostat.
MSD 6AL ignition.
MSD Blaster 2 coil
MSD tach adapter.
MSD adjustable timing control.
Trunk mounted battery.
Mickey Thompson Indy Profile S/S tires, rear.
Crager Drag Star polished aluminum wheels, 15x8.
Monroe adjustable air shocks, rear.
South Side Machine weld on Sub Frame Connectors.
Cloyes double true roller timing chain set.
Cyberdyne speedometer calibration box.
Mildly tinted windows.

Don Moore

 

wow, what does that thing run?

 

And you call that thing a fairly modified 91 formula????!!!!
Should call it "my fairly modified dragster"
Do you have any dino numbers for that...thing?
How about pics of it? I'm sure we all would love to see some pics to believe that all that fits inside one car...
Sorry but I don't know about your problem. Well, I had an 88 firebird that used to do something like that: It might drive fine fora week, and then suddenly it would stop running. Then it would fire right up. It ended up being the control module inside the distribuitor.

 

I tried to post pictures, but i get an error message. I guess I don't know how to do it right.

Don Moore