Ok, i have a '94 GMC S15 Jimmy 4x4 with the 4.3L cpi engine. Did a fuel pressure test and with engine off and for 2 seconds after key is turned over pressure is at 56 psi, but after 2 secs it drops to 50 psi and with engine running at idle it is art 50 psi. With ignition off it stays at 50 psi but drops to 40psi in 5 minutes and to 20psi in 15 minutes. Sounds like I may be replacing a fuel pump soon. Just replaced fuel injectors/ fuel pressure regulator with reman unit as well as fuel filter in the last few months. Fuel pump was replaced about 2.5 years ago and ran for about 4 months than sat for 2 years while engine was rebuilt. Maybe sitting for so long ruined it? Or am I completely wrong and these results are acceptable?

 

Oh, and the issue I am having is that the engine idles well but has no power when accelerating and feels like it is misfiring and backfires a little too when engine is under heavy load.

 

https://blazerforum.com/forum/tech-a...agnosis-23038/

this has all the information for fuel pressure testing