I have an 02 blazer with 4.3l v6. Its had an intermittent problem with missing for the last 2 years. Idle is a bit rough, mostly misses when giving gas while driving. First time it had the problem, I changed out plug wires and it ran perfect for a few months then slowly got worse again, then did spark plugs, also fixed it for a few months. Then did cap and rotor, also helped for a while. A while later I did the plug wires again. Same thing, fixed it for a while then back to missing. Seems like there is some electrical component that is weak and every time I replace something, its just enough to compensate. I have a few ideas to try, but they are getting more expensive. There is the ignition coil, the alternator (voltage regulator built in) and the battery. One other problem it has that makes me suspect the voltage regulator is the headlights and interior lights will sometimes pulse while the car is running. Especially when I turn up heater fan or turn brights on. Would a bad voltage regulator cause engine missing? It also has a problem with the battery dying if it sits for more than a day. Napa tested my battery and said it was good so that also makes me think bad alternator or voltage regulator. Trying to decide what component to try next between alternator/voltage reg, or ignition coil. Any advice would be appreciated.

 

This is almost certainly a fuel pressure problem. Either the fuel pump is not suipplying enough pressure or the check valve is bad or the problem may be the regulator whis is part of the spider assembly under the upper plenum on the intake manifold, Due a pressure and leak down test. there is a test port on the fuel line next to the throttle body. It must read 60 psi key on engine off and hold it for ten minutes after turning key of. If it doesnt it is mostlikely the fuel pressure regulator bleeding down or fuel pump check valve is bad. The spider is the most likely problem they are notoriously troublesome.

 

I was suspecting something fuel related, but why would the problem temporarily go away when I replace the spark plugs and wires?

 

Just went out and did the test. When I turn the key on, it instantly came up to 58psi. After 10 minutes it was at 50. Is this acceptable? Or is that too much of a leak? Should I try some sea foam in the fuel? It really does act like its fuel related, I just don't get why the problem would go away for a month when replacing plugs and wires.

 

It needs to be at least 60 PSI and you should not have any leak down. This is a possible fuel pump related issue but the fuel pressure regulator can not be ruled out either.
It looks like you may need to go the same route I did and start with a new fuel pump. Be sure to use an AC Delco or OEM Dephi unit. Do not substitute for a less exspensive part it will not be worth it. If that does not resolve the issue then a new injeection spider will be needed as the fuel pressure regulator is an integral part to this unit and can not be replaced on its own, Besides the new updated spiders are a much better design and well worth the effort to replace them. Again Only use an AC or Dephi part.