I have a 1995 Blazer ls 2dr 2wd 4.3 with 170K. has always ran well. Approx 8K miles ago the fuel pump was replaced with new delco unit. 2 weeks ago after a 200+ mile drive it started missing and the longer I drove it the worse it got. If you gave it gas as it started to miss it would clean out, but as soon as the rpm leveled out it would start to miss again. finally as I let off of the gas as traffic backed up it died and would not start. After letting it set for about 1 hour it started like nothing had ever gone wrong. I was afraid to drive it so I trailered it home. Fuel pressure was 55lbs, checked the FPR area for leaks and all looked good. replaced the ECM and drove it around locally for a week and all was well. Took it on another 200+ mile trip and at about 185 miles it started missing again and progressively got worse. on arrival I let it idle and it ran smoothly, when gassed it would stumble but then clean out. The next day it would not fire. towed home. when I went to show someone how it would not fire it started perfectly and runs fine. I have let it idle for hours with no problem, but now im afraid to drive it over 150 miles.... where do I start.

 

Fuel filter, cap, rotor

and I think your fuel pressure should be a little higher... is that when it's running?

Check the pressure when the pump cycles and before you start

 

Thanks drperry
I neglected to say that the fuel filter was replaced at the time the new fuel pump was installed. I well replace the cap and rotor just because. In reviewing the symtoms it seems like it may be pulling a vaccum on the tank or a problem with the cat converter or muffler being plugged up or restricted, is it possible for those to cause these problems. How do you test for a restricted exhaust system.

 

It could be... For the gas tank vacuum problem... Make sure you tighten the cap until it clicks...

sometimes, if the cat is bad, it'll rattle if you hit it with something, or if it's really really really clogged, it can supposedly start glowing red after awhile...

 

Almost looks like you are having a very similar problem to what I am experiencing. I also thought it was the Cat converter so I replaced mine, but that was not it.

https://blazerforum.com/m_86234/tm.htm

Let the truck warm up then drive it around the block a few times (don't go too far just in case it acts up on you). Try putting a load on the engine by turning the AC to MAX AC and the fan to full blast. After about 30 minutes my truck will start acting up like yours does. When it does act up, hook up a fuel pressure gauge to it and let us know what the pressure readings are. Also listen to the fuel pump when it primes the system, does it sound normal?

I will let you know when I figure out extacly what is causing my issue. Please let me know if you find out what is causing yours also. Thanks.