Ok, the 2.8 is finally running in my 84, after I hooked up the fuel injectors. Now after fixing a vacumme leak, my engine is now making popping noises, like if someone is making popcorn, not full out, but like, pop, de pop, pop, pop, de pop, something like that, and its not the exhaust I think and its not backfiring. Is it a rod maybe?

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Proud owner of a Bright Red 1993 Grand Prix SE, 3.1 V6, 4 speed on the floor, fully loaded, very nice

In Progress Restoration/and attempt of a 1984 SE, to be powered by a 2.8 V6.

1984 SE converted with 86 GT parts being parted out, pm me with requests.

Possibly the injector harness is intermittant? Or has a mechanical pressure gauge been hooked up while engine is running?
I like being first response, it allows me to guess the easy stuff first. I have not followed the history of your swap so do not know where you are at, so don't get mad if I seem to patronize. The four cylinder fuel pump won't feed the injectors on the six. It sounds like a fuel mix problem to me (that's one out of eight thousand) so more vacuum leak somewhere is still very possible. Hope it turns out simple.

fuel pump's been replaced with a v6 delco, maybe its the catalytic convertor?

Check for exhaust leaks and insure that your timing is correct @10*BTC. Done a compression check to look for a leaking valve (lash adjustment?).
Just a few common things, a bad rod will sound like someone knocking on the door.

The old chevy 283's used to pop like that through the carb when the cam was wiped out. Pull the air cleaner hose off and take a ride to see if it gets louder. Hope it doesn't!
Kevin

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85 Fiero-based ASPP GT-40 MarkII. 3800 S/C, Auto, Held suspension all around with 2" drop spindles and sport fr. end. RCC bump-steer correction. Mr. Mike's interior.

I'm pretty sure I got my timing reset, I moved it back and forth finding the best area the engine likes to run in, and it idles at about 1200-1500 rpm's. I did think I heard about the cat making popcorn popping noises when it was bad? Of course this cat's only got 50,000 miles on it from 86.

quote Originally posted by 1985FieroGT: I'm pretty sure I got my timing reset, I moved it back and forth finding the best area the engine likes to run in, and it idles at about 1200-1500 rpm's. I did think I heard about the cat making popcorn popping noises when it was bad? Of course this cat's only got 50,000 miles on it from 86.

So you set the timming by ear?
Use a light to get it in the rest of the way.
Sounds more like an exhaust leak, check the rear header for cracks. Leaks at the "Y" pipe and other connections of the exhaust.

It does have a crack on the weld on the 5th cylinder, the exhaust manifold by the trunk wall. About an inch through the weld.

quote Originally posted by 1985FieroGT: It does have a crack on the weld on the 5th cylinder, the exhaust manifold by the trunk wall. About an inch through the weld.

You just found the source of the popping. Good luck removing that exhaust manifold.