So my buddy and I were off-roading with my 2003 ZR2 and we got a little stuck. After calling for help my buddy's dad came by with his truck and chained us up and tried pulling my car out. I let my friend try to guide the car out, but he stayed revving it at like 5k for about 15 seconds and pieces of burning metal started shooting out of my tailpipe. I yelled at him to stop and all was well. Once I get home, I realize that the vehicle is running rough at idle, but is fine when under load/power. I drove around a bit, and I swear to god I lost an eighth of a tank after driving down 2 miles with a little aggressive acceleration. Well, 2 months later and I still cant find the god damn problem. The injectors/ Fuel Pressure Regulator passed the leak down test, the intake gasket was replaced recently, MAF is clean, TPS is good, IAC valve is good, entire exhaust system is new, and the air/fuel filter is also new. I was thinking about putting a 5.7 in her soon, but I would really like to figure out what this problem is first. Burnt valves maybe? Any suggestions?

 

Misfires will show up on a capable scanner using the Misfire Counter PIDs. Just display them all and see which one has misfire counts that are going up. Certainly the misfire is turning on the SES light, right? Alternatively any scanner should be able to tell you which code was set. P0301 is cyl 1, p0304 is cylinder 4, etc. p0300 is random misfire. Hope you didn't get rid of the cat converters. That will turn on the SES light for sure.

If you attempt a 5.7 swap on a second gen blazer, use the vortec 5.7 and retain the fuel injection and PCM. Otherwise it will be a big hack job. Doesn't NY emissions testing prevent a lot of engine swaps. Also could be a problem if engine is older than the vehicle, and a 2003 might require a LS engine swap if it matters in your state. Fortunately for me I live in Indiana! We don't have vehicle inspections here.

 

Time to do a compression check and/or leak down test on all cylinders. Start engine, pull fuel pump fuse, let engine die and then get started pulling all the plugs out. Also place something to hold throttle body open before doing compression check, not needed for leak-down test.

Just a suggestion.