How do I test my external electric fuel pump

[kat]

So been having some fuel delivery problems that has popped up all of a sudden. I have checked anything mechanical dealing with my fuel delivery system and want to check the electrical side of things.
I have a Carter P4594 mounted on inside of frame, and has been there with no issues. I am running a 4 barrell carb on a 351W. I know this thing has a built in regulator and was wondering the best way to test it while still on Bronco. I read where it has 4.5 amps at max pressure so it should fluxuate correct? What do I need to do? This weekend I plan on crawling under to check any loose/broken wires and want to put a multi meter on it.The pump still whines so I know its working but maybe not working the best. BTW the pump is about 3 months old with a clear in line filter before it and after it. Thanks

 

[fluffybunny]

You could try installing a fuel pressure gauge to see if you're getting proper psi.

 

[Teal68]

Mark,
I agree with fluff. "T" in a pressure gauge as close to the carburetor as possible. Use a long piece of hose from the "T" to the gauge so you can tape it to your windshield. That way you can see the psi under all conditions. My bet is your filter closest to the carb may be clogged.

Hope you are doing well!

Tyler

 

[pcf_mark]

I would remove any filter before the pump. Electric pumps push really well but the are terrible at sucking through any restriction. That is one of the reasons modern cars have the pump in the tank.

 

[Rustytruck]

I would check the voltage at the pump both at the battery to make sure the voltage at the battery is actually getting to the pump both when first started and after it gets warmed up.. I would pull the end of the fuel line and pump into a can and see if flow volume is up to spec. Make sure you have good ground. just where is the pump mounted? any chance it is getting overheated? maybe an exhaust shield

is needed. on this pump Carter requires a pre pump filter. if the pump is failing you need to send this filter in with the pump for warranty replacement. when this pump was installed what did you doe for safety? oil pressure switch or roll over switch or nothing? maybe these subsystems are having a problem? check your wire connections at the pump to assure they are staying tight. I am assuming you have a relay to run this pump so check voltage going into and out of the relay. I am in the middle of installing a carter P4070 pump myself.

https://static.summitracing.com/global/images/instructions/crt-p4070.pdf

 

[Broncobowsher]

Fuel pressure gauge by the carb inlet, route it up toward the windshield, go drive and get your issue.
If the fuel pressure holds, you are not looking at a fuel supply issue. If it drops, we can start going through what it is.
I will recommend keeping the pre-filter. If you have a stock tank the original pre-filter sock in the tank has probably fallen apart by now. Aftermarket tanks rarely have a pickup sock. That pickup sock is the factory pre-filter and is engineered to be there for a reason.

Air leaking into the fuel line before the fuel pump can cause a LOT of issues. Ever try drinking from a straw that has a pin hole in the side?

 

[jamesroney]

So been having some fuel delivery problems that has popped up all of a sudden. I have checked anything mechanical dealing with my fuel delivery system and want to check the electrical side of things.
I have a Carter P4594 mounted on inside of frame, and has been there with no issues. I am running a 4 barrell carb on a 351W. I know this thing has a built in regulator and was wondering the best way to test it while still on Bronco. I read where it has 4.5 amps at max pressure so it should fluxuate correct? What do I need to do? This weekend I plan on crawling under to check any loose/broken wires and want to put a multi meter on it.The pump still whines so I know its working but maybe not working the best. BTW the pump is about 3 months old with a clear in line filter before it and after it. Thanks

Sometimes the view is not worth the climb...

Adding diagnostic features and testing and measuring is the proper way to troubleshoot. But for some things...It can be easier to throw parts at it.

I would buy another P4594 pump and install it. If the problem goes away...it was the pump. If the problem persists...now you have a great spare pump.

I seriously doubt if your problem is the pump...but if it IS an internal issue in the pump motor causing an intermittent problem, it can be torture to catch it when it is mis-behaving. Vastly more likely that you have a fuel restriction problem, or a voltage delivery problem.

Everything else posted above is also valid. I'm assuming that you have a tricky, intermittent issue...and you have already done the appropriate fuel delivery, pressure, and flow rate tests.

 

[kat]

Thanks for all the advice. I have done all mechanical problem solving I can figure. Fuel sending unit is not that old but pulled it and took the sock off the pickup, still didn't help. Filters before and after the pump are new and not clogged. I have found WITHOUT having a filter before pump I was picking up trash and it was getting stuck in the veins.
The pump is where it has always been which never gave me issue for 3 years. The pump is not that old, I replaced it because I was having the same issue so I already have a spare pump.
My gut feeling is wiring of some kind. Are everybody connections on the pump covered with supplied wires? Or is the pos/neg exposed?
I do like the idea of fuel pressure gauge, but after I crawl under and check the wires with my brand new handy dandy multimeter I might install one.

 

[pcf_mark]

If you really think it is the wiring hot rod it. Run a new good clean ground wire and new positive from the battery to a switch in the cab then out to the carb. Just tape it in place of wires to keep it safe not win a beauty contest. Easy and cheap test. My money is it is not that but a piece of mind is good to have so test it.

Rusty Truck has a good idea - if the voltage running at the pump is the same or very close to the battery voltage you know you are getting volts. If there is enough amps is hard to measure. But if you hot wire like I said it is 100% new, solid connection see if it changes. If not go back fuel restriction.

If you have the specs for the pump it should tell you how many gallons per hour - turn into gallons per second and just run the pump with the hose into a gas can to see if it delivering.

 

[kat]

Well I THINK I found the problem. I had a sketchy ground wire so rewired it. Drove to town, filled up both tanks and drove her for about 2 hours straight with not even a hiccup.
But walked by it today and gas was coming out of the filler neck tube. When I filled it up and didn't go past one click of the pump so I know it wasn't overfilled, especially driving it for a couple hours. So now I'm down another path to see what is going on. Now she sits out in the sun so I know the gas is expanding in tank so there is definitely a venting issue. Hope to look at tomorrow.

 

[Broncobowsher]

Thermal expansion. I did that a few times. Fill both tanks, go for a drive. Heat will expand the fuel (and vapors) and so long as you have driven a little bit there is room in that tank for expansion.

I made it a habit to drive one tank a few miles then switch to the other and run it down. There was a hole in the asphault parking lot at work for 15 years (until they repaved) from the main tank dribbling out on a hot day after filling on the way to work.

 

[kat]

Thermal expansion. I did that a few times. Fill both tanks, go for a drive. Heat will expand the fuel (and vapors) and so long as you have driven a little bit there is room in that tank for expansion.

I made it a habit to drive one tank a few miles then switch to the other and run it down. There was a hole in the asphault parking lot at work for 15 years (until they repaved) from the main tank dribbling out on a hot day after filling on the way to work.

So yours only did it when you filled both tanks at the same time?? Like I mentioned, I filled them up and drove it on main tank for a good while. So I should have drove a few miles off the aux tank??

 

[Oldtimer]

My 68 came from factory with Aux tank.
The Aux tank had NO vent.
I don't know how PO lived with it, but it was one of the first things I fixed.

 

[1970 Palmer]

My 68 came from factory with Aux tank.
The Aux tank had NO vent.
I don't know how PO lived with it, but it was one of the first things I fixed.

The early trucks had a short reach gas filler cap. They vented the tank through the cap vent. Not having a true tank vent, also made them a PITA to fill at anything more than a trickle. The later trucks got closed (sealed) fuel systems to meet the coming emission requirements and they have sealed caps.