another 4.3 running like crap
 

i just picked up a 99 zr2 blazer, has a miss when i bought it... really bad, was sitting for a couple months, the guy didnt have money to put into it so i picked t up fairly cheap... has 170xxx miles, got it home, did normal stuff, cap, rotor, coil, plugs, wires, fuel filter.. fixed acouple vacuum hoses. ran better but not perfect... ran a compression test all cyl. between 115 -125 psi.. ran a fuel pressure test, just key on goes up to 62psi.. at idle bounces between 52-56 psi.. i replaced the spider with new updated version... runs better but still stumbles and misses... mostly under medium throttle between 1500-2100rpm and at idle... not sure what else to do ... i removed the cat. and gutted it.. had code p0300 for miss fire, cleared it out light hasnt been back on... had a code p0452 evap pressure sensor signal low/ short... cleared hasnt come back.. also when i take fuel tank cap off it releaves pressure.. none of my other s10s have done this.. any help would be great!!! thanks for your time...

What brand did you use for the tune up? Have you cleaned the MAF sensor? Usually a random misfire is always do to secondary ignition componets.

Accel cap,rotor,coil... duralast wires...ngk plugs...cleaned maf already

These things only like ACdelco cap, rotor, coil and wires.

Ngk plugs do well in these motors

Thats what i have been reading, but i dont see how it would effect it... accel stuff has to have better fire than acdelco..only down fall i bought would be duralast wires

I took a brand new cap out of the box installed it on mine and chased a cylinder #1 missfire for 3 weeks before I listened to this forum and brought a delco cap, The forum was right! cap was the issue, and visually the other cap looked perfect

i will do alil more digging if nothing else looks like ill start buying parts again... kinda sux if i have $150 worth or parts i cant use..

clean the EGR valve?

swapped it with one from a spare engine i have no change