Hey guys I just installed my fuel pressure gauge and it's reading 60 psi, but when I give it 1/2-3/4 throttle it dumps down to 50 psi. It does rebound to 60 psi when I let off the throttle. Is this normal? I checked my racor and I am getting a few super small air bubbles coming into the filter. Im going to pull what ever is left of my hair out with these damn air bubbles, Thanks for any help

 

Mine stays between 60-62 PSI, if I mash the pedal it will drop to 58 or 59 but only for a split second then it will rebound back to 60-62 even if my foot is still into it. So I would say no, that is not normal.

 

I have an Autometer with the sensor post filter and new pump with FRX, my pressure is at 63, on throttle it drops to 58ish. Where is your sensor mounted? What brand gauge?

 

autometer installed post filter

 

Ok, so what does filter look like and do you know how old your pump is?

 

filter is good, and I'm pretty sure the pump is original. Maybe the pump is getting weak? Or does this have anything to do with the fpr spring?

 

The FPR "could be weak".

Perform an AMP Draw on the Pump. You can do this by several ways, at the Pump for a Delta, and then at the Fuse Block to monitor when putting under load.

Do the Same with a "T" and Pressure Gauge just AFTER the Pump. I use an old 10' section of Ait Line with Couplers and Bungee the Gauge to the D/S Mirror.

If both those are withing Specs. Seek a failed Check Valve in one or both Heads, or a restriction in the Fuel Lines to either Head.

 

The ONLY way you are going to eliminate any chance of air getting in the fuel is to fully pressurize the entire fuel supply line between the fuel TANK and the engine. Only way to do that is to relocate the fuel pump to inside the tank. I did that ten years ago on my 1999 F550 and it was the single most effective modification that I ever did for that truck.

 

This is the fuel sending unit that I modified with the pump for my 550.

 

I had an issue with fuel pressure loss because of air in fuel. The full Hutch mod with removal of the quick disconnects was the answer. Even then, I struggled a bit with the hoses being properly clamped, until I double-clamped.

I run at 60 PSI (with a FRx), and I have 160/100 injectors on my stock fuel pump. I can make the pressure drop to as low as 50 PSI at WOT in high RPMs, but it always snaps back to 60 PSI.

 

The spring does make a difference. I replaced my pump last fall because I didn't know how old it was and although there wasn't an issue it was obvious it was very tired once the new one was running.

 

that is a great idea wish I would have done that. When I turn the key on engine off the pump turns on and stays at 58 PSI until the pump shuts off then I lose almost all pressure within a few seconds. Is that normal?

 

you lost me at Delta, LOL. If the fpr was week wouldn't I be getting pressure spikes? This is all new to me so just trying to learn, thanks

 

i did the double clamps and got rid of the quick disconnects. Those air bubbles are going to be the death of me. they are not nearly as bad as they were with the little plastic filter though. with koeo fuel pumps up to 58 psi but when it shuts off the presure drops to 0 with in 3 seconds, is that normal?

 

The Delta is merely the Pump Pressure Measured at the Pump, with Engine NOT running - "No load".

All following test pressures relate to that pressure [Delta] to determine where an obstruction is or perhaps a failing pump.

As for the FPR Spring - Not always the case. Eventually, the spring (all springs) will loose their ability to hold closed the Pressure Disc. The pressure at the FPR should be essentially the same as what's occurring in the Bowl for Supply. The Spring collapses until the pressure is near equal.

Some of these tests will point you in the right direction.

As for the falling pressure, is it the Feed or Return Side. You need to figure that out as well. Essentially, the pressure should maintain for a period of time as any other Fuel Injected System. These are Low Pressure Supply Systems as they are actuated by the High Pressure Oil on the Head.

How long? I don't have that answer. But, I will seek it out this weekend for you.