Bad fuel pump signs?

Chadsjeep

New Member
Jan 18, 2020
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Hello I'm new here so bare with me. I have a 94 jeep y2k with a 93 5.0 302 swap(efi) it sat for about 5 years due to a bad distributor and I finally got it running. Ran great for about a month then it started to spit and sputter and randomly die. Now its to the point that it will start right up but shuts right back off. Changed the fuel filter ran great for all of 5 mins and right back to where it was... I have a bbk fuel pressure regulator on it and my guage on the cluster will read 40 psi and hold.... As soon as it starts it fluctuates... Please any help is appreciated.
 
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7991LXnSHO

wanna catch the space herp
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Sep 1, 2010
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If the vac line is hooked up to the regulator, it is supposed to not be a steady pressure while running.
As far as signs, a high pitch whine has been a sign on two other vehicles that needed pumps. They also did not have as much full throttle power and mileage slipped. But the last two symptoms were so general to not be as helpful as the pressure and noise.
 

jrichker

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Mar 10, 2000
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What type and year wiring are you using to run the fuel pump - Ford or Jeep?

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the EEC test connector and jump the connector in the Upper RH corner to ground.

attachments\68357


Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.
 

7991LXnSHO

wanna catch the space herp
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Sep 1, 2010
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@jrichker to the rescue! I could not remember the second part of the test enough to be sure.

Do higher volume rated pumps also make more pressure when blocked like this test? I am speculating about what the ability to move more fuel through the same line has.
 

Blown88GT

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Nov 13, 1999
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@jrichker to the rescue! I could not remember the second part of the test enough to be sure.

Do higher volume rated pumps also make more pressure when blocked like this test? I am speculating about what the ability to move more fuel through the same line has.
They sure do, 100psi or more. Fuel will blow out past many clamps & fittings.