89 iroc 5-spd, originally a 305. I spun a bearing in the 305 7 years age, car sat in a barn for 5 years, replaced engine with a used 355 out of another iroc tpi car. The car ran ok, but above 3000 rpms at full throttle it just missed, backfired and fell on its face. I assumed it was a bad distributor, but as soon as I started the car with the new engine it was knocking so I didnt worry about it then. I parked the car for two more years.

About a month ago I started the second engine swap. The new engine I just had built by a good engine shop (the local chevy dealership recommended it). Bored 40 over, fordged everything, corvette tpi aluminum heads, and a 4/7 swap cam w/510 lift and 112 lobe seperation. Put in a used msd distributor from a friend of mine (his car was running fine when he took it out) to fix the high rpm miss.

Got the engine in and running on monday. Idles a little rough, but the big problem is that at 1500 rpm's it misses, and pops out the exhaust. It runs so bad that even with the throttle wide open it will not go past about 1700 rpms (or any throttle position in between WOT and idle). I read on another post that the ESC module and knock sensor need to be changed when changing to a 350 but if you unplug the knock sensor it will run ok. I have my knock sensor unplugged with no change. The timing is set right, not 180 out.

I am checking the fuel pressure and ignition voltage today.

Any info would be helpful. Has anyone had a similar problem and fixed it?

Thanks

 

I replaced the distributor with my old one and it fixed the popping and backfiring, but its still missing.

 

Start with simple stuff, do you have spark at every cylinder? Is it a random misfire or is it a certrain cylinder? One way to check this (not the best way, but it works and is easy) is to pull the spark plug wires 1 by one and see if it misses worse, or if there is no change, the one that has no change is the problem cylinder.

Also, are all your injectors plugged in properly? I know thats a dumb question, but there are lots of connections involved in a motor swap, its easy to overloook one.

 

Its a random misfire, all the injectors are plugged in. Its running really rich, I'm thinking its time to have it tuned.

 

Random misfire...those are fun..hmm