Engine/Transmission (1998.5 - 2002) Lift pump going bad??

[66gt350]

I'm trying to find out if my lift pump is starting to go bad or if it is something else.



The past couple of mornings it's been a little cooler than normal out here in California. I'll start up the truck and have good fuel pressure, between 14-15 psi. I'll drive a little ways and all of a sudden the fuel pressure will drop to under 5. I can turn the truck off and then right back on and the pressure will be back to where it belongs. Normally, it does that once and it's fine. This morning it was the worst its ever been. I had to do that about six or so times before it operated normally. After it warms up, it has no problems, and the truck can sit here at work all day and won't have any problems. I was under the impression that the bearing would get hot and quit working, but then why does it only happen first thing in the morning?



Is this the lift pump going out, the sender on the fuel pressure guage, or something that could be causing this? Any help would be appreciated.



Thanks

Rob

 

[Casey Ray]

What type of gauge, electrical or mechanical? If electric, could be your grid heaters drawing on the circuit and affecting the gauge, once the truck warms up, the heaters don't factor. I've noticed the same thing on my truck, once it warms up, the gauge reads as it should.



Bocifus

 

[66gt350]

I am running an electric gauge. I don't believe that it is associated with the grid heaters, because after the gauge goes down, it doesn't comeback up until I turn off the engine.

 

[Jetson]

My original fuel pump would only show 2 psi when it was cold. I started cycling the key before I started the truck. After 3 or 4 times pressure would come up and be fine the rest of the day. Eventually, it took 10 or 12 times cycling the key before I had good pressure, and I replaced the pump. The pump sounded pretty sick, like it had a bad bearing.

 

[Casey Ray]

Do you have anyone that you can borrow a fp test gauge from. Like the one from Black Mountain?

<http://www.blackmountaindiesel.com/contactus.html#pressuregauge> I am going to get one just to make sure my sending unit isn't going south. This is my second lift pump and this problem <?> only started after the dealer replaced the 1st pump. So I am a bit concerned as you are.



Bocifus

 

[66gt350]

This lift pump only has less than a year on it, and I don't drive the truck much in the summer. It will have good pressure warming up and as I leave, but after a short while it drops.