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Michael Moore
Michael Moore, GM MASTER/WORLD CLASS. ASE MASTER
Category: Chevy
Satisfied Customers: 2866
Experience:  ASE Master/GM WORLD CLASS/GM Master/GM ASEP/Dodge Gold/Mazda cert.
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Running fuel pressure be on a 1997 Chevy S10 4.3L engine

Customer Question

what should the running fuel pressure be on a 1997 Chevy S10 4.3L engine
Submitted: 4 years ago.
Category: Chevy
Expert:  Michael Moore replied 4 years ago.
What is the pressure after turning the key off? Check to see if the fuel pressure drops to zero, if it does then how long dose it take?
Customer: replied 4 years ago.
No the pressure stays up maybe drops to about 40or so pis over time.
Expert:  Michael Moore replied 4 years ago.
The specs for the pressure from GM is 60-66psi with the pump on engine off, engine running should be 60-64psi. The pressure should not drop below 50 psi within 10 mins after turning the key off. The problem is the fuel pressure regulators have been known to leak on these trucks. Your pressure drops a little more then it should but its hard too tell if your regulator may be causing a issue. Its best to check the pressure over night. What happens is the regulator leaks raw fuel into the intake ( the regulator is located inside of the intake) and this will cause a hard start and even black smoke when first started. Also your fuel pressure is a little low wile running, but how good is your gage?
Customer: replied 4 years ago.
After running the engine to warm it up. After 10 minutes, this time,the gage is holding at 61psi. Again the running pressure is 51-52psi. Then goes up to 61psi when the engine is shut down. I'll wait and see what happens over night. A little background on the truck. It has 173K miles and has had the fuel pump replaced in Aug of 2004. Idle is a little rough and will occasionally run in a fast idle until you kick down the gas pedal. i.e. the truck will run at 25mph without the cruse control or application of gas.
Customer: replied 4 years ago.
Ok, Now after 2 hours the pressure has bled back to 22psi. Engine started fine. Pressure back to 61psi at shut down.
Expert:  Michael Moore replied 4 years ago.
Let me know what happens in the A.M.
Customer: replied 4 years ago.
First thing this morning ...checked the pressure. It was down to 0. Turned the key on pressure up to 61psi but it took three tries to get the engine to start. Running psi is still at 51-52psi. Could it be that the pressure reg is letting to much cycle back to the tank?
Expert:  Michael Moore replied 4 years ago.
Its possible. There can be a few causes. First, there is a check valve on the fuel pump. This valve keeps pressure inside the fuel line. If this valve is leaking down it can cause this issue. Next is the fuel pressure regulator is not holding and letting fuel back to the tank. Third and most common on this truck, the fuel pressure regulator is leaking fuel externally and flooding the intake. To check, pressure up the fuel lines then pinch both lines off with a fuel line clamp (or vise grips) to stop the flow of fuel. If both lines are pinched off and the pressure still drops, the regulator is leaking, if it holds, then release one of the lines until the pressure starts to drop. If its the fuel supply line, then the check valve inside the pump is bad, you will have to replace the pump. If its the return line, then the regulator is bad.
Customer: replied 4 years ago.
OK Michael I'll try that this weekend and get back to you. I am leaning toward the regulator at this point.
Expert:  Michael Moore replied 4 years ago.
Let me know what you find.
Michael Moore, GM MASTER/WORLD CLASS. ASE MASTER
Category: Chevy
Satisfied Customers: 2866
Experience: ASE Master/GM WORLD CLASS/GM Master/GM ASEP/Dodge Gold/Mazda cert.
Michael Moore and 5 other Chevy Specialists are ready to help you
Customer: replied 4 years ago.
Well I replaced the pressure reg and that seems to have fixed the problem. That was not an easy task. Price was about $90 for the gaskets and the regulator. Thank you for your help Michael.

Regards,

Mike
Expert:  Michael Moore replied 4 years ago.

Glade to help.

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