1996 Chevy Blazer-misfiring engine

My blazer died on me one night on my way home from work. My boyfriend checked the fuel pressure and realized that the car needed a new fuel pump. While he was replacing that, he also replaced my spark plugs, & wires & distributor cap. The car started right up, ran beautifully and then started to misfire. We then replaced the fuel injector harness, it ran great for three days and began misfiring again. Whenever we try to scan it, it says the car is misfiring on a different cylinder. We replaced the plugs again, and it was ran good for a day or so, then started to misfire again. The problem is intermitent, so it has been hard to diagnose. We don't know what else to really do at this point. Any advice?

Have you looked into the egr valve? Common problem for these trucks. Does the truck seem like the exhaust is getiing bottled up? If you let it idle then try to take of and it feels like it is running rough or missing, it could be the egr

when it missfires try tapping the EGR and see if it clears up

I asked my boyfriend about the EGR valve last night, and that's working fine, they have already checked it-thanks!!

This probably does help much, but my father had a intreped that ran bad when it wanted to and it ended up being a bad computer. He would be doing 55mph and the car would just start to skip and missfire. Hopefully that is not your situation.

Actually, that's what we're concerned about. If it's the computer, that's a ton of money. At this point, we still have no clue. The mechanic wants nothing to do with me anymore because he cannot figure it out! Thanks!

I would look into getting a parts truck with a 4.3 motor to get the computer from. You would need the computer of course. Or even a junk yard would have the computer for you. Maybe a few hundred dollars. If you knew somebody with a similar truck that could maybe let you test theirs with your truck that would be very helpful. Even Ebay might have something like that. Check there first.