95 blazer runs rough

My sister 95 blazer runs really rough. we just swapped motors in it and had it a a mechanics shop for two months. He had gotten it running smooth and told us if it had ever happen again that the egr valve was probably to blame. A month after driving it around it started acting up again. It was backfireing so bad it blew the muffler out.Ii replaced the egr valve which made it worse so i put the old one back on. it still ran rough so i trailered it to my house. When i unloaded it it ran fine, i parked it in my back yard and was going to but new exhaust on it. When i started it today it started running rough again. The check engine light has not came on yet even when running it with out the egr valve pluged it. That same mechanic told me the computer may be fried. But he is known for messing with the lights and other stuff so you will bring your vehicle back to him. This motor has been a pain in the ( l ) since it was swapped. If anybody has any ideas of whats wrong i would greatly apperciate your input. Thanx

But he is known for messing with the lights and other stuff so you will bring your vehicle back to him.

Then why would you take it to him in the first place?

What was the new motor out of? What year? Injection type?

the motor was out of an s10 truck its a 95 It is a 4.3 ltr. And the only reason it was took to him was because he was the one that found the motor for us and he warrenttied the motor, that is why.

How about you take it back to the mechanic and have him fix the engine he installed that is not running right.

It is HIS job to fix it, not yours.

he got the motor out of a salvage vehicle so he only gave us a 90 day warrenty. he got it to run but it took him 60 of the 90 and now the 90 is up

So what, if the problem occurred before the 90 day warranty was up, he still has to honor it.

The 90 day warranty should have started when you got the thing back, not when you took it to him.