I have the prime loc system installed on my truck. It has two test ports where the filter mounts. I have been told one port is pre filter the other is post. Put the sending unit on the outside test port and am getting just under 25lbs. I am going to switch to the other port and see what i get. I hope the pressure will go up. If it does, i will know i am seeing the pressure pre-filter. This is probably the better of the two places. What do we think?

 

I would put it post filter since that is what really matters in the end. It will also help you with when to change your fuel filter then.

 

Put it at the inlet to the IP. Drill and tap the bajo bolt and install a Tee.

 

Im gonna switch it over to the other test port and see what happens. I agree that fuel pressure after the filter is what counts. If it stays at only 24psi max, then it might be time for a new lift pump. Im gonna change out the fuel lines just as soon as they show up. It might have a little bit of an air leak. I put on a new filter right after the guage install and it made no difference in fuel pressure.

 

Before you go replacing the lift pump pinch off the return hose with pliers.
If the pressure shoots up the lift pump if fine, overflow valve is the problem,

 

Well, i pinched off the return line and the pressure did go up. It went up to just a little beyond 25lbs. like around 30 or so. So we think this might be a weak overflow valve? Im gonna pressurize the tank here pretty soon to check for leaks. Its gonna upset the wife if i buy an overflow valve, and then i tell her im gonna have to buy a lift pump. I have a holley blue i was gonna install. Ive been told that wont help anything. Let me know fellas!

 

It should have gone up over at least 60 psi when you pinched the line.
Lift pump is bad, supply line kinked or tank or heater screen clogged.

 

Well, thats enough work to keep me busy. Would a bad lift pump cause it to lose prime? One in a while, it will either crank but not fire, or fire for a second and die. Its obiously not getting fuel. This is a relativly new phenominum.

 

When one of the unfortunately nonreplaceable plastic check valves in the lift pump fails it can lose prime.
My experence with this failure is that fuel tank level or parking the truck nose uphill can make the difference between a hard or easy start.