Howdy. Just replaced the fuel pump on my 1999 Blazer 4 door LS. Got a Delphi fuel pump. Got 2 readings of 56 psi on initial key on only pressure checks. Is this a good pressure reading? I am still experiencing some misfire or rough running when at idle and in gear, like at stop lights. Read elsewhere that it should be at least 60 psi, but it was not clear what year the Blazer was.

Thanks for your comments.

 

Your pressure is good if the pump is off. When your not using the pump prime terminal or the blazer isn't running the pump isn't running. When you cycle the key on without starting the pump only runs for 2 seconds. If the pump was primed pressure should hit 60 in those 2 seconds but if you don't keep the pump running pressure immediately drops to about 55 and then very slowly leaks back to the tank. 55 while the blazer running has been good for me. The correct way to read pressure at the service port is with the pump running and the engine off.

 

should stay above 55 with key off for ten minutes. If not then you need to do a tast a the filter exit to determine if its the pump or spider/ regulator

 

Thanks guys. Very helpful.
I think I am going to replace the EGR valve and see what happens regarding the misfire before I do a recheck on the plug & coil wires. So far since January I have replaced the CPI Spider with a MPFI Spider and new regulator. Also, spark plugs(Iridium), distributor, fuel line, and fuel pump. I figure the coil is the next weak link, but the EGR valve could be a easier fix, I am told. Hope so. Will keep you all posted.

 

How are the sparkplug wires also, is it the same plug misfiring?