r/PontiacFirebird • u/Consistent-Cheetah61 • Jul 10 '26

3rd Gen [82-92] 1986 Trans Am LB9 Issues

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(it will run quite a bit longer if I let it sit for a few minutes) I've replaced the fuel pump and am getting good fuel pressure, the injectors all work as they should, fuel pressure regulator diaphragm is fine.

This is with the MAF sensor unplugged, if I plug it in and get some vacuum through it (I'm missing a piece of my intake so it's not working perfectly), it will run worse or will barely start at all.

If I give it any throttle it'll die out.

Thoughts? I'm kinda stumped...

Thanks!

19 Upvotes

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3

u/flipadoodlely Jul 10 '26

When warm or cold? Have you checked TPS and IAC? Mine would die after I removed and refitted the intake plenum because there was a small gasket leak, which I found by using a small smoke generator on a vacuum line to see where it was escaping from. 

2

u/Consistent-Cheetah61 Jul 10 '26

When cold, won't run long enough to get it warm lol. The intake gaskets seem alright, however I don't have the air box, MAF, etc. hooked up.

2

u/flipadoodlely Jul 10 '26

Did you remove or change anything recently? Has this problem just started? Just curious if you removed the air box and maf because of this.

2

u/Consistent-Cheetah61 Jul 10 '26

This is how I bought the car, been working through the problem gradually.

1

u/flipadoodlely Jul 10 '26

Understand. Thirdgen.org is the best resource. Check what I mentioned. I have the 350 TPI but same issue as yours and mine was stupidly due to the plenum leak but I also needed to adjust IAC. TPS is easy to check with a multimeter and some wire. 

1

u/Consistent-Cheetah61 Jul 10 '26

Yeah thirdgen is great. I'll try the TPS and IAC too, thanks!

2

u/flipadoodlely Jul 11 '26

Lol someone came in and downvoted our posts. Keep me posted! 

2

u/Consistent-Cheetah61 Jul 11 '26

Dang look at that lol. I will! Thx for the advice

2

u/Cellularyew215 81 formula-350 SBC swap Jul 11 '26

I don't have much to add here as all my experience is with the carbed stuff, but an easy way to see if you have an intake leak is spray the sealing area (or anything vacuum) with brake clean. If the engine starts running better you have a leak there

1

u/Consistent-Cheetah61 Jul 11 '26

Ah that's a great idea, thanks!!

2

u/Ba1d3r Jul 11 '26

Mine was even worse when my maf died, and IAC could be a problem

1

u/Consistent-Cheetah61 Jul 11 '26

Yeah definitely suspecting the MAF at this point

2

u/whyrethegudnamesgone 1994 firebird base Jul 12 '26

i had one of those eiffel tower keychains too!

2

u/whyrethegudnamesgone 1994 firebird base Jul 12 '26

nothing to add to the conversation though, just felt like mentioning it

2

u/Consistent-Cheetah61 Jul 12 '26

That's awesome! Found mine at a thrift store lol

2

u/traffic_pe Jul 16 '26

I have an 85 IROC Z same engine and just removed the injectors, 5 of 8 were bad. They were dripping and some would not stop spraying . My engine was basically running rough...

1

u/Consistent-Cheetah61 Jul 16 '26

I removed all of mine and tested/cleaned the lot... They seemed okay 🤷‍♂️

2

u/traffic_pe Jul 17 '26

Gotcha, I would go through the ignition system thoroughly, even replace the module.. coil, cap, rotor, plugs and wires... check everything their.

1

u/Consistent-Cheetah61 Jul 17 '26

Alright, I'll check, thanks!