For the past month and a half or two months my 91 Z28 has had some really bad sputtering issues, car goes really quite for a second and then kicks, seems like it wants to go but feels like its lagging not getting any power. If I hold the gas in while it will be making small backfire sounds like its clogged while sputtering. It seems to happen alot more often around 30-50 mph in 4th "OD" sometimes if I have it in "D" as well. If you turn the car off after all of this and the turn it on after waiting about 10-15 minutes it will have an incredibly bad idle. I have had these issues since I had my new Borla cat back exhaust system put on and can't figure out what is going on.

I had the the garage replace the plugs, wires and distributor cap with a full tune after a previous issue about 3 or so months ago. So a two weeks ago I hooked the car up on my scanner and found nothing. I took it to my buddies garage who put the exhaust on for me and he had his tech hook it up on the transmission scanner and engine scanner and also found nothing. I just in the last 3 weeks had the oil and trans fluid flushed and changed and its still doing it. The heat shield on my cat had fallen off and had it welded back on last time I was at my buddies shop. I think the catalytic converter might be clogged or messed up, I really don't know the signs of that The cat converter is the original from the factory so I think that that might have something to do with the issue.

I don't know what is going on here so any help or suggestions are welcome! I thought of getting a highflow cat put on see if that can do the trick. Or is it sound like possibly my fuel pump is going?

Car info:

1991 Camaro Z28 (TPI 305)
700R4 Automatic
141k miles on all (engine, trans ect.)

Borla 3" Catback (200 miles ago)

 

Have you checked your injectors.

 

Possibly a bad o2 sensor. They can cause numerous gremlin-like behaviors. So can a vacuum leak.

 

Check the exhaust back psi b4 the cat.
Ohm check the injs cold and hot (if stock).
Check fuel PSI
make sure the tune up shop didn't leave a plug wire close to the exhaust and burn thru a wire. (my guess)

 

I was thinking injectors as well.

Had a similar issue 3 or 4 years ago. Bad idle, up and down, near stall at stop lights. Incredible backfiring in 3 or 4rth (manual).

Checked the original bosch injectors with a volt meter for ohm reading. I think they should be around 13 or 14 ohms or so (don't quote me it's been awhile). I remember 2 of them were reading at about 16 or so and 1 at about 8.

Replaced them with a new set of Ford SVO 24 lb'ers (blue tops) and she ran like a champ afterwards.

 

Turned out to be a combination of a bad starter and bad fuel pump. The fuel pump was low on pressure and starter was boarder line fried and eventually died at a gas station. Thanks though guys. The car runs as clear as day now.