Archived lift pump problems

[BRI7070]

After hooking up my gauges ( fuel pressure takne at schread valve at VP-44), I had found that the stock lift pump would run at about 12 psi for 5 minuets then it would quit. If I shut the motor off then restarted it I would have the 12 psi again for 5 minuets then quit again. I decided to replace the stock lift pump and relocate it to the frame rail just in front of the tank.



Heres what I did,

I cut the stock steel line just in front of the tank and added a 3/8" hose to a Carter 4601HP electric fuel pump (100GPH / 14PSI) mounted just behind the transfer case . Using 3/8" fuel line ran up to the fuel filter stepping down to 5/16"line and used the stock banjo fitting to connect and from there it is stock. for the wiring I used a 30 amp relay to connect battery power (fused) to the pump and tapped into the stock lift pump wiring for a signal to activate the relay. After all was connected I test ran the setup, turned the key to the on position and the pump ran for a few seconds at 13 psi then shut off. I bumped the started to run the pump for 30 seconds and it did at 13 psi. All is good so I started it . runs perfect. 13 psi at idle, 7psi wot.



Heres my problem,



After a week, I start my truck this morning and all is fine. go to the store and on the way home I see that fuel pressure is down to 6 at idle and 0 at wot. Shut off the motor and restarted it and still have the low pressure.



What is going on? I have checked all my mechanical connections and going to check all my electrical connections and voltages shortly. Any Ideas? Did I buy the wrong pump?



TIA

Brian Arnold

 

[Gary - K7GLD]

Before ANY other trouble shooting is attempted, I would change the fuel filter - even if it's only been a rather short time since the last change - often dirty fuel or debris will plug the elrment as long as fuel is flowing - but will drop off when the engine is shut down - and then slowly accumulate on the element and plug it again as the engine is operated next time...



Of course, that is also true of any other fuel filters you may have added along with the new pump - there SHOULD be one installed between the 4601 and the fuel tank...

 

[BRI7070]

hey Gary how are things going? Will you make the next meeting? I will be there.



I went out and got a new fuel filter after I had posted the topic and about to go change it now. I also got a volt meter to check the voltages. dont see how that could be an issue the waty it is wired but it is a good enough reason to get one. After I check the filter I will let you know.



Have a good day

Brian.

 

[Gary - K7GLD]

Not real sure about the next meeting Brian - if weather is real good, might take off during that time with the RV and head north for the week - my wife sorta vollunteers at a local small church school, and it will be their spring break - but if not, I'll be at the meeting...



Hope a simple filter change does it for ya - sure easier than some of the other possibilities...

 

[BRI7070]

??in tank???

Well I change out my fuel filter and now I have 0 psi. Checked for pre filter pressure and 0. Checked for out put from pump and no output. I have disconnected the input line to the pump and nothing. I can blow into the line and hear bubbles in the tank so I don't believe that I have a restriction there. Now have to figure out how to get the prime back. When I first did the relocation the tank was full and it self primed, and now I have half a tank and nothing is coming out.

Also when the lift pump was in the stock location I had never lost the prime when changing the filter.



Well, going back out to try to re prime the lift pump

 

[Bob Wagner]

Read This





buy a threaded banjo bolt

 

[Gary - K7GLD]

NAHHhh - you havea pump problem - that thing should self-prime with no trouble - I use a similar pump on my transfer tank, and it NEVER fails to prime...



And I realize "mileage varies" - but I have used the Shrader valve at the VP-44 as my takeoff point for my fuel pressure guage since it was installed, and my readings are entirely stable, no problems on ANY kind...

 

[BRI7070]

OK here we go.

I returned the system back to stock, leaving the pusher in place but electrically disconnected. hit the key and the stock lift started and got 12 PSI almost immediately. So I hooked up the pusher and pegged my 15 PSI gauge. I did not like that so I disconnected the power from the stock lift pump and the pressure dropped from pegged to 12 PSI. OK, so I shut the motor off and went to restart with the pusher and no pressure. I bumped the motor to get the 30 second run time and plugged in the lift pump the guage pegged. At this point I thought that the combination of the 14psi pump and the lift pump was to much so I replaced the 14 psi pump with the 7 psi pump. Both are carters 100gph pumps #4600hp(7psi) and 4601hp(14psi). once I had replaced the pusher I hit the key and pegged the gauge. Well I disconnected the pusher electrically and went for a test run with the stock lift pump. After about 20 minuets the stock lift pump shut down so while still running I hooked up the pusher and pegged the gauge. At wot the pressure would drop to 12-13 psi. and peg itself At idle.



I got home and disconnected the pusher and was trouble shooting the stock lift pump and noticed that after shutting down the motor and going for a restart I turn the key to the on position and the lift pump would not come on. and when I bumped the key the lift pump would come on for about 2 seconds. If I were to wait a few minuets it would act normal. Am I looking for an electrical/electronic gremlin?

 

[BillGotthelf]

I think the ECM controls the electric to the lift pump. It cycles the lift pump at idle to prevent over pressurization in the VP44. If you are using the stock lift pump wire to trigger solonoid for add on pump and if the signal isn't there no pressure from either pump. Just a guess on my part-someone more familiar with lift pump control needs to speak up.