hey im stuck i have a 96 s10 blazer and i developed an occasional miss that turned into an occasional misfire. i had the codes read and it said misfire on #1 ive changed the plugs,wires, cap and rotor. the problem got a lot worse. now it misses at idle and when i rev the motor it misfires. i traced the vacuum lines and they seem fine, well all the ones on the diagram under the hood anyway. it sounds like i may have a doughnut gasket leak would this cause my problem? i should mention that i have the 4.3 vortec v6. any and all advice is welcome......

also i should mention that i tried to unplug the vac. line where it runs to the rear of the vehicle while it was running and there was no change in the motor

 

A tune up should not have caused the problem to get worse. How did the plugs look?

If you have an exhaust leak in the area of the 'donut', it can throw off the O2 sensor readings causing a rich condition.

 

the plugs where worn quite bad it looks like they where in the truck for some time. but would that cause the misfire issue?

 

Plugs with too wide of a gap could definitely cause a misfire condition, but that 'should' have been remedied by the tune up.

What brand of plugs did you install? What were they gapped to?

 

Another thing to make sure of is make sure none of the spark plug wires are touching, in cheaper sets the spark can jump across to another wire causing all sorts of fun things.

 

If the misfire got worse after tune up it seems most likely that something went wrong with the tune up. Make sure plugs were gapped properly, make sure wires are going to the correct cylinders, cap n rotor both screwd down tight, and that you have all o the wires connected good at both ends. and NEVER use autolite plugs on a GM

 

kk ill double check these things tomorrow. ill let you guys know what i find

 

i have a miss in my #1 cylinder too. i got my 96 blazer worked on a month and a half ago. the LIM needed replaced when i got it back i had a miss in the first cylinder and it was not there before it got worked on. the place told me i had miss and it could be the cylinder or the injector. i found out form a friend that when they took my intake manifold apart they had to remove the injectors and they could have been damaged in the process and that is why it has a miss now. the place that worked on it wont fix there possible mistake at their cost since they messed up so my friend is gonna work on it for me. the spark plgs and wires are fine according to the place that worked on it but i know i cant trust what they did because im having my blazer worked on again for overheating which the place was supose to fix. i was told the miss wasnt bad but it is you can hear it its slow to start and when its idoling you can feel it. what could cause the miss if the place didnt mess it up?