I can sure use some help with something that has been going on about 3 months. Whenever I start my 96 Blazer it pops 2-3 backfires, sounds like nearer the front rather than tailpipe; then after that it runs just fine, not rough at all. This problem is worse when it is cold; after the engine has warmed up, and even sits for 2-4 hours, it will always start, sometimes with the popping sounds, sometimes starting normally as it is supposed to do. A couple of times, it refused to start at all, so I decided to try something--I drilled a small hole for easier access into the plastic air intake just above the throttle body ( I use a small metal screw to seal it afterwards.). I then sprayed some starter fluid into the throttle area beneath the hole I drilled. The car started right up! So, this tells me, at least I think it tells me, that it may be a fuel delivery problem. I still have not fixed the problem, but I need some good help in what I should diagnose. I will appreciate any and all suggestions.

 

Sounds like an issues I had with an '80 GM Sierra Grande years back. The coil was shot, it would start sometimes & other times not. Frusterating as all hell & it backfired once & sent the muffler into the great wide yonder (never found it or even parts of it lol) Also could be a timing issue & yeah, fuel delivery. Have you checked the fuel pump, hear it spin up when you turn the key to Run but don't start it?

 

I would start with a fuel pressure test. See what it goes up to as well as whether it bleeds down after the pump shuts off. The details are in the link found in my signature.

 

When I replaced the fuel filter, I turned the ignition on in order to see if the fuel pump was pushing ample fule out; it squirted out about 4-5 inches, which I figured made the fuel pump good. I will resort to a pressure test soon. I had autozone put a code reader on it and no codes showed and it read as a "pass". Thank you both so much for responding by the way.

 

The fuel pressure needs of your engine are very specific. A gauge is the only way to verify that the pump is functioning properly.

 

I went to a different autozone location and the scan showed there that it was o2 sensors or catalytic converter. Could these sensors malfunctioning make it backfire on startup only?

2nd question: is there a relay somewhere under the hood for these sensors? (the fuse box next to driver side fuses # 4,5,9 and 10 were all good.)