Engine/Transmission (1998.5 - 2002) Droping Fuel Pressure

[Forsberg]

I'm having a problem diagnosing a problem with my 99 5. 9L. I have a 5 month/10K mile transfer pump and new fuel filter element. When I start the engine, all is well. Fuel pressure is 14 PSI at idle on both the input test port and output test port on the filter. After 30 seconds, pressure drops to 3 psi. If I shut of the motor and restart, same effect. It is consistant with both a warm motor and cold. There has been no noticable differance in performance with the motor other than 1 MPG less mileage. I've blead the air from the low pressure system without an issue. I would like to know if it could be something other than the transfer pump. ;#@$%! Any words of wisdom would be greatly welcomed.



Gary

99' 2500, EDGE Tow Pro

 

[Partyat33]

This might not be too helpful, but when your grid heaters turn on, it can really reduce the fuel pressure.

 

[rjrkihap]

Hi



Had similar issues (with two pumps). One minute it was normal then it would drop instantly to 7 then next day to 6 and finally to 0. I am on my 4th lift pump (now on the frame). The second was dead within a week (bad right out of the box). Initially the pressure would quickly return to normal and then a few moments later drop back down. Over the week it would continue to drop lower and lower staying at the lower pressures longer and longer.



When my 3rd lift pump started this routine (after a year in service) I paid Rip and Bob at Source to put the 4th pump on the frame. I probably should have spent the $$$ on a FASS but Quadzilla and Mag Hytec were already in line.



Good Luck.



Ron

 

[Forsberg]

Thanks for the help. I know I want the pump on the frame, I was determining getting the FASS transfer pump (warrenties help)

 

[mhenon]

I'm having a problem diagnosing a problem with my 99 5. 9L. I have a 5 month/10K mile transfer pump and new fuel filter element. When I start the engine, all is well. Fuel pressure is 14 PSI at idle on both the input test port and output test port on the filter. After 30 seconds, pressure drops to 3 psi. If I shut of the motor and restart, same effect. It is consistant with both a warm motor and cold. There has been no noticable differance in performance with the motor other than 1 MPG less mileage. I've blead the air from the low pressure system without an issue. I would like to know if it could be something other than the transfer pump. ;#@$%! Any words of wisdom would be greatly welcomed.



Gary

99' 2500, EDGE Tow Pro

Don't know what kind of gauge you have but that sounds just like the problem I was having. Turned out to be air in the isolator. It drove me nuts for awhile but cleared up for good once it was fixed.

Mike

 

[Hookemupman]

My truck is doing the exact same thing. When you first start it it has 14 psi of pressure about 20 to 30 seconds later it goes to around 2psi. If you shut truck off and do it all over again the same thing happens over and over. Do any of yall have any ideas?I also checked with a mechanical gauge with the same results. I am just about ready to order a air dog. Thanks Jason

 

[JLandry]

Do any of yall have any ideas?I also checked with a mechanical gauge with the same results.

Jason,



Assuming the lift pump is being told to pump fuel as it's supposed to, then...



Could it be a mostly-blocked strainer screen inside the fuel tank? To find out, maybe you could disconnect the fuel line at the lift pump and blow some low-pressure compressed air through the line back into the fuel tank. If that happened to cure the problem, it would probably be only temporary and you'd have to drop the tank for cleaning.



Or could the lift pump be sucking air from a crack somewhere in the fuel line or maybe in a fitting near the top of the tank?



Maybe a collapsed or kinked fuel line between the tank and lift pump?



Just some wacky ideas to think about.



Good luck,



John L.

 

[ChrisWilliams]

You may have a collapsing suction line and/or a restirction in the tank.

 

[draymorris]

I like the heater scenario - the easiest to solve - do nothing. I mounted my lift pump on the frame a few weeks ago and withing days heard the pump noise changing in the morning. Figured out that it was the heaters cycling.



I also believe that you could have a blockage. To me the easiest way to test would be to open the filter drain and see if the pressure really does change. If it does I would look remove the pump, disassemble it and see if the screen is blocked, before I dropped the tank to look for trash. If it was blocked with some trash I think I would be tempted to go ahead with a frame mount system and place an inline screen before the pump.



I may be wrong, but I don't think the pump has enough suction to collapse many types of hoses - and it would need a blockage to create that kind of suction - so your back at the blockage problem.



Air coming in from a leak would be another issue to look at when you are pumping through the filter drain.



Let us know what you find.