I have a 1991 blazer 4x4. its a plow truck. I've done a full tune up on it. double checked everything. nothing is off. all wires are where there suppose to be. but now its back firing thru the exhaust and the throttle body. any answers?

 

I believe it a throttle body injection system correct me if wrong.Did you adjust timing when you tuned up truck? and when you did, did you also unplug wire under passanger carpet near dash while timing?

 

well ty for your return replies. thanks to the retards that make these parts, they stamped the number one cylinder in the back of the distributor cap. so me pulling my hair out trying to figure out what I did wrong, wasn't my fault. lol ive spent 3 days trying to figure this out. so I just had a buddie come over that has the same truck and went through his. found the problem that way.