have a guage on my fuel pump it reads 55 psi when key is in on position and about 52 psi when running when i shut off key it drops to about 20 psi over the course of about 5 to 10 minutes can someone tell me if this is normal cuz ive been having a very hard time getting it started when its cold and then after about 5 miles of driving it bogs down and sputters if i give it too much throttle now i just went out and turned it back on it read 60psi and when i shut the key off this time it didnt lose pressure whats this mean

 

It's common for fuel pumps to fail in these from what I see. When you put the key in the on position can you hear the fuel pump whine?


What year is your truck? Most late model 4.3L model V6's require at least 60 PSI of fuel pressure (key on, engine off) and usually decrease in pressure (from starting pressure) anywhere between 3 to 10 PSI with the engine at idle. Your fuel pressure shouldn't more than 5 PSI from the your engine off starting pressure after 10 minutes.


It sounds like you either have a fuel pump issue or fuel pressure regulator issue. You can test for these by blocking the return fuel line on your fuel system. There are three fuel lines going to your fuel pump (largest is pressure line, one is EVAP, and the other is return fuel). If your return line is properly blocked; when in the key on position your fuel pressure will either skyrocket past 55 PSI (Pump good, Pressure regulator bad) or will stay the same (Pump bad).

 

oh I def hear it whine i just replaced the tank before all this started and never heard the pump like i do now its def louder than it was nor did i have this problem before i chand
ged the tank

 

oh its a 1996 4.3 blazer

 

and if properly blocked and both pump and regulator are good what will it read 0?

 

If the return fuel line (the excess fuel going back to the fuel tank) is blocked and your pump is good you may see pressures as high as 100 PSI (the pumps for these trucks are powerful); if it's stuck at 55 PSI the fuel has nowhere to go, it's the pump. I've seen this test in person at a shop, but was with a car that had fuel rails the return line was blocked at the rail. Blazer's with CSEFI don't fuel rails making the this fuel pump test a little tricky.

If the pump and regulator are good it's something else in the fuel system. I didn't think to mention it before, have you replaced your fuel filter. At only about $20 it's easy replacement that will at least give you peace of mind and it could if fact be the fuel filter, a clogged filter can give you the symptoms you described above.

If the pump and pressure regulator are good and the fuel filter is new check the fuel injectors. I've seen these fuel injectors call it quits (we had a GMC Jimmy with a rough running engine that quit in the middle of the shop floor, new fuel injectors fixed it and it ran like new).

Also, since these vehicles are known ignition issues too. Make sure it isn't your ignition system. I speak from personal experience on that one, my truck died last night in the drive way.

 

And here's the specs for engine off, key on fuel pressures at your truck's model year.
VIN X: 55 - 61 PSI
VIN W: 60 - 66 PSI
The 8th digit of your truck's VIN will tell you which pressure your truck should be at.

 

I havent changed the fuel filter yet I will do that and let ya know and thanks for the specs
on the psi requirements I appreciate it