Hi all

I bought a 91 Firebird 3.1 V6 in December and all I've done since then is chase an intermittent misfire/idle issue.

It had other problems too which I've fixed along the way thinking it might of cured this problem but it's still there. The previous owner replaced the fuel pump. The car then died when I tried to start it a few weeks after getting it but it had been ok until then. That turned out to be the fuel pump relay.

I've changed the fuel filter. New fuel injectors from south bay as the pressure was dropping to zero after priming the system. That's fine now. New fuel pressure regulator. Some new vacuum hoses where needed. New plugs and leads. New MAP sensor. New IAC valve. New TPS. Still ran crap.

lastly I've just fit a brand new dizzy today as the inside of the old one was looking pretty corroded around the reluctor...... And still runs crap with that too!

the car starts right up and idles. Then you notice it's got a slightly miss. It was running about 10 minutes and suddenly dropped about 400rpm then slowly recovered. Then idled ok for a few more minutes and done the same. It does that a few times.

I've only tried to drive the car twice and it's worse when driving. You set off and it's missing quite badly under load. Just regular acceleration to get the car going and it's missing terribly. Felt like it was going to cut out as I turned around at the end of my street to try and nurse it back home.

I've also tried two spare ECUs from the same year car and it remained unchanged.

I'm just starting to feel at a loss now. My friend who has the same year car and engine thinks it will be some sort of electrical problem with how up and down it is and intermittent. Or possibly a bad knock sensor?

but any ideas where to go from here are greatly appreciated!

Thanks

 

Just curious, since you say it appears to be an ignition miss, have you tried a new ignition coil?

I ask because your list includes plugs, plug wires, and a whole new distributor which I presume must have come with a new cap & rotor, leaving the coil as the only part left original?

 

The coil had been changed by the previous owner too. It still looks very clean and shiny. The old one was in the box of spares that came with the car. That's one thing I havnt checked actually now you mention it. Possibly a faulty coil?

 

I swapped out the computer on my 86 Iroc because the car just never ran good. I bought a used one on ebay for $15 shipped. Car ran like new.

 

I've tried 2 other ECUs that I know to be good and the car was exactly the same

 

Swap in the spare coil, see if anything changes. If not, unplug the O2 sensor, see how it drives.