I own a 99 blazer that I have been dealing with a miss at highway speeds lately and on ocassion I have a miss on 45 mph roads with the ac on. Did a fuel pressure test and when i turn the key on it only raises to 20 or 30 max. Turn engine on and it jumps to 52 at idle. driving around it stays 52 to 55. Come to a stop and park turn key off and the pressure will actually jump up to 60. Wait for ten minutes and it leaks down 10 psi in ten minutes. Don't know how to apply vacume to the fuel pressure regulator to see if it is working properly or not. But I do have a definite starting issue after it sets over night. Been cycling the key on a few times to see if it makes a difference with it starting.

99 blazer
189,000
4.3

 

Sounds like you have a bad fuel pump. Especially if it's the original fuel pump - considering your mileage.

I did a few tests myself last week and finally was able to trace my problem to the fuel pump. Not knowing the type of fuel pressure tester you have you may want to try what I did on my Blazer. Connect the gauge directly to the fuel filter, you can use a small piece of 3/8" inside diameter fuel rate tubing, and do the same test you conducted before but this time your numbers should be very different (just turn the key to on and off to prime the pump - don't try to drive). Connecting the pressure gauge directly to the fuel filter will allow you to test for maximum fuel pump output pressure. The number should be between 73 psi and 108 psi., and remain above 55 psi for 10 minutes after the pump shuts off. If this does not happen, then you need to replace the fuel pump.

Also, when was the last time you changed the fuel filter?