Engine/Transmission (1998.5 - 2002) high fuel pressure, anybody know why?

[ScottWright]

Recently I noticed that my fuel pressure was really high. My SPA guage shows it bouncing around, but it's as high as 40psi. At first I thought it was the guage, but I switched my fuel pressure and my boost guauge, and got the same results.



I have an old style Fuel Preporator on the truck, along with the factory lift pump. I can run either system, but I can only run them seperately. There is a silinoid between the two that controls which inlet is open. So when the Fuel Prep. is turned on, the fuel can only flow from that inlet. When I turn the factory lift pump on, it switches the inlet so only the lift pump inlet is open.



What's interesting is that no matter which pump I run, the fuel pressure is very high. Not quite as high on the factory pump, but still over 30psi.



The high pressure has caused some hard starting lately. If I wait for it to bleed some pressure, it fires right up.



Any idea what could be causing this? Does the VP44 have an internal fuel pressure regulator for the inlet pressure? I thought it only controlled the internal rotor vein feed pressure, and the high pressure, I didn't know it even could control the inlet FP?

 

[Todd T]

where are you picking up your pressure reading from, pre or post fuel filter? have you cleaned the fuel heater screen lately and how old is the filter?

 

[ScottWright]

The fuel pressure is picked up just before the VP44 inlet. The fuel preporator fuel system bypasses the stock fuel filter all together, so I'm reading just before it goes to the VP44. Where is the fuel heater screen? I ordered fuel filters today for it anyway, I'm due to change them anyway.

 

[BarryG]

Could it be the solenoid crapped out. ? I am not familiar with the preporator or how it is plumbed. However I would start with unplugging the harness from the stock pump and see what happens to the pressure. Then hook it back up and remove the power from the prep and see what happens. I also use spa gauges and from past expereince they do not like air in the gauge line. When that has happened to me I can get really high pressure readings but they usually jump around alot, extreme spikes both high and low.

 

[ScottWright]

I had also thought maybe the solenoid was the problem, but I don't think it is. The way it's wired/plumbed is.

There are two seperate fuel lines from the tank. One is the stock set, and there is a seperate fuel line from the Fuel Prep. In my case they "T" back together just before the Injection pump. They come together at that solenoid. There are 2 inlets (one from each pump feed) and 1 outlet. When I turn on the fuel prep. system, only the fuel prep. turns on. The solenoid is also wired on the same switch so it bypasses only the fuel prep. inlet. When I flip the switch, the fuel prep. turns off and the factory LP turns on. The solenoid switches over letting the LP inlet work, while closing off the Fuel Prep. inlet. I unplugged the solenoid and turned on the factory LP. I can hear it running, but no fuel pressure, which leads me to believe that the solenoid is doing it's job.



It's interesting what you said though about the SPA gauges. Mine definately presure spike. The fuel pressure reading is very unstable. 40~25 even at idle. I don't see how it could have air in the line though, because it's threaded right into the fuel line. If it does have air in the line, that means the whole fuel system has air in the lines! Which is obviously a very bad thing!!!

 

[BarryG]

Mine has gotten air in doing a filter change before but I had a 3ft 3-an hose from my fuel line to a needle valve to my sender so there was a place for the air to get trapped unlike just the main fuel line itself. Well if each pump seems to be working correctly, the solenoid is working and the gauge is working properly. Only leaves a couple things I think. One they are pumping that much pressure which seems unlikely at least for the stocker and especially both of them seperately. Or second there must be a restriction somewhere past the solenoid. Could be in the line from the solenoid to the vp or further inside the vp. Maybe (sorry dont know the part names) the fuel bypass valve is not opening fully/partially blocked for the return fuel. Or a clog/partial blockage of some sort in any of the internal plumbing of the vp before the actual high pressure pump inside it. Maybe even the return line on the way back to the tank is somehow partially blocked or pinched.



Have to admit just guessing and thinking out loud.

 

[Todd T]

is it possible your return lines are plugged, melted or kinked shut or extremely restricted? I take it the SPA guage doesnt have an isolator on it? if not you should invest in one and fill the line to the guage with glycol.



put a manual pressure guage on at the pump and see what you have.

 

[monkeyman]

You will blow that VP44 out in no time flat if your pressure is that high, I did!

Rick