I was driving my 90 blazer w/4.3 and never had any issues. I parked it monday afternoon. 1 week later on monday morning I have a crank/no start issue. Here is the thing that has me stumped. I have spark, I have good fuel pressure and the injectors are working, the timing is also there so what else can it be. I have tried a known good map sensor and oxygen sensor and will be trying a coolant sensor tommorrow but I don't beleive it is any of these. It really wants to start but then either pops thru the throttle body or every now and then thru the exhaust. It really acts like it is out of time but it isn't. Did a compression check and lowest was 130, highest being 142. I was thinking a head gasket failure but not sure now. Any help is greatly appreciated.