Low Fuel Pressure after replacing pump - JeepForum.com
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post #1 of 23 Old 05-18-2020, 10:11 AM Thread Starter
Zuber87YJ
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Low Fuel Pressure after replacing pump

I have a 1987 YJ with a 2000 4.0L I6. I have an external electric fuel pump and I have replaced the fuel pump, fuel filter, dropped the tank and checked the sending unit and have replaced all of the rubber lines. Tested fuel pressure at the fuel rail and at the pump and it does not go above 20 PSI, I’ve bled the fuel lines and there are no fuel leaks. Fuel pump is also getting 12v to it. What might be the issue and where else should I troubled shoot? Thanks!!

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post #2 of 23 Old 05-19-2020, 06:49 AM
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Did you replace the pump because of low pressure or another reason?

93 YJ SOA 2" springs front, XJ springs rear w/main leaf added, High pinon 9 inch rear detroit locker front Dana 44 ARB 4.56 Gears, 36 inch Irok tires too much to list.
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post #3 of 23 Old 05-19-2020, 07:02 AM
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YOur jeep is a 1987 the engine is 2000.

Did you use a fuel pump for a 1987?
>> What is the rated fuel pressure ? SOmething like teens IIRC
I am to lazy to look it up...

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 23 Old 05-19-2020, 10:29 AM Thread Starter
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I replaced the fuel pump because the old one failed while out driving and it would run for maybe 15 min and then cut out.
No I did not put an 87 pump in, an 87 engine is not fuel injected. I have an external electric pump system so I replaced the external electric pump similar to the one I had before it failed.
The rated pressure is 49 PSI (+\- 5) at the fuel rail and I’m not getting over 20, most of the time it’ll stay at 10 and then drop to 0 with out the engine cranking.
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post #5 of 23 Old 05-19-2020, 10:42 AM
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Quote:
Originally Posted by Zuber87YJ View Post
I replaced the fuel pump because the old one failed while out driving and it would run for maybe 15 min and then cut out.
No I did not put an 87 pump in, an 87 engine is not fuel injected. I have an external electric pump system so I replaced the external electric pump similar to the one I had before it failed.
The rated pressure is 49 PSI (+\- 5) at the fuel rail and Iím not getting over 20, most of the time itíll stay at 10 and then drop to 0 with out the engine cranking.
Without pictures/brand names/part #'s there are a lot of assumptions to make. I am assuming that the old pump system ran for quite awhile before crapping out, and you haven't relocated or changed anything in the run.

Where are you measuring pressure, and with what device?
Is it an identical replacement, or just similar?
Are you running dead-head or through a regulator?
Do you have a return/recirculation line?

I'm guessing (totally) that the diaphragm or seat is bad in the new pump and it leaks internally, based on what you have stated, but I really don't know because it's not enough.
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post #6 of 23 Old 05-20-2020, 09:44 AM Thread Starter
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Quote:
Originally Posted by gutthans View Post
Quote:
Originally Posted by Zuber87YJ View Post
I replaced the fuel pump because the old one failed while out driving and it would run for maybe 15 min and then cut out.
No I did not put an 87 pump in, an 87 engine is not fuel injected. I have an external electric pump system so I replaced the external electric pump similar to the one I had before it failed.
The rated pressure is 49 PSI (+\- 5) at the fuel
rail and I’m not getting over 20, most of the time it’ll stay at 10 and then drop to 0 with out the engine cranking.
Without pictures/brand names/part #'s there are a lot of assumptions to make. I am assuming that the old pump system ran for quite awhile before crapping out, and you haven't relocated or changed anything in the run.

Where are you measuring pressure, and with what device?
Is it an identical replacement, or just similar?
Are you running dead-head or through a regulator?
Do you have a return/recirculation line?

I'm guessing (totally) that the diaphragm or seat is bad in the new pump and it leaks internally, based on what you have stated, but I really don't know because it's not enough.
Very true, I’ll take some pictures and add them later today. The old pump did run for quite a while and I have not changed the configuration or relocated everything but I have tried that as a potential fix with no success.
I’m using a fuel pressure test kit borrowed from Oreilly’s and have tested pressure coming from the rail, the pump directly, after the pressure regulator before heading to the rail, pretty much everywhere possible using a T line splitter to connect to the tester.
It is identical since I did not put the original pump in, I was thinking it might be a faulty new pump but I have tried other pumps similar to it as well so I’m doubtful that so many pumps are bad and producing the same result.
I’m running through a regulator but have tested before and after the regulator in order rule that out.
The return line runs from the regulator back to the fuel tank.
I’ll add some pictures later for some added clarity.
The pump I have in currently is Oreilly part number E16138
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post #7 of 23 Old 05-20-2020, 01:01 PM
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Might sound like a stupid question but, are you sure you have it going the right way?
How about the electrical connections are they wired the right way too?

93 YJ SOA 2" springs front, XJ springs rear w/main leaf added, High pinon 9 inch rear detroit locker front Dana 44 ARB 4.56 Gears, 36 inch Irok tires too much to list.
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post #8 of 23 Old 05-20-2020, 05:53 PM Thread Starter
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Yeah I’m confident that everything is connected properly, also tested the connection and made sure it was getting 12v

Here are some pictures of it, it’s not the clearest but the tank is dropped right now so it’s below but you have the sending unit in the tank with hose going to the filter, to the pump, to pressure regulator which has a return line attached that feeds back into the tank and then from the pressure regulator up to the fuel rail.

I’ve tried 3 different fuel pumps that are all similar and multiple configurations, also tested the pressure right after all pumps before going into the PR.
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post #9 of 23 Old 05-21-2020, 06:56 AM
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Have you inspected the pick-up inside the tank? Corrosion or rotting rubber can partially block the inlet.
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post #10 of 23 Old 05-21-2020, 08:14 AM
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if you dropped the tank and replaced, are you positive that none of the lines were pinched?

"money talks, mine always says goodbye"
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post #11 of 23 Old 05-21-2020, 08:16 AM
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Quote:
Originally Posted by gutthans View Post
Have you inspected the pick-up inside the tank? Corrosion or rotting rubber can partially block the inlet.
this too. the rubber nipple on my sending unit basically turned to silly putty.

"money talks, mine always says goodbye"
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post #12 of 23 Old 05-21-2020, 10:08 AM Thread Starter
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Quote:
Originally Posted by danthman View Post
Quote:
Originally Posted by gutthans View Post
Have you inspected the pick-up inside the tank? Corrosion or rotting rubber can partially block the inlet.
this too. the rubber nipple on my sending unit basically turned to silly putty.
Yeah I took out the sending unit made sure nothing was blocking it and replaced the mesh filter, no issues with it and no pinched lines, all of them have been checked and made sure that they are clear. Very stumped, does anyone know if the external pumps take time to build pressure?
the one I have should be pushing 75+ PSI but tested it yesterday just after the pump and did this with the other two pumps I’ve tried as well and it will hang around 10-15 PSI while the pump is running and that’s only when the engine is attempting to run and get nothing when the key is turned and the pump runs for about 3 seconds
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post #13 of 23 Old 05-21-2020, 11:56 AM
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Quote:
Originally Posted by Zuber87YJ View Post
Yeah I took out the sending unit made sure nothing was blocking it and replaced the mesh filter, no issues with it and no pinched lines, all of them have been checked and made sure that they are clear. Very stumped, does anyone know if the external pumps take time to build pressure?
the one I have should be pushing 75+ PSI but tested it yesterday just after the pump and did this with the other two pumps I’ve tried as well and it will hang around 10-15 PSI while the pump is running and that’s only when the engine is attempting to run and get nothing when the key is turned and the pump runs for about 3 seconds
its a good idea to bleed the line going into the fuel rail. I had to on mine. are you sure that your regulator is good? I have alittle different setup on mine. I have a 4.2 with the mopar efi kit on it and im not using a regulator... or at least its not like yours and I havnt found it. look at the pump to see what the output psi is. mine has it stamped on the housing.

"money talks, mine always says goodbye"
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post #14 of 23 Old 05-21-2020, 02:36 PM
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How about get rid of the fuel filter and then check the pressure?
I run my filter after the pump. Just what I am thinking as long as there is a screen to filter out any big particles, you should not need a filter before the pump. I wonder if the filter is slowing down the pressure and making the pump work harder than it needs to. That would explain why your old pump went out.
Oh and you can get rid of that trac bar on the rear!

93 YJ SOA 2" springs front, XJ springs rear w/main leaf added, High pinon 9 inch rear detroit locker front Dana 44 ARB 4.56 Gears, 36 inch Irok tires too much to list.
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post #15 of 23 Old 05-21-2020, 08:19 PM Thread Starter
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its a good idea to bleed the line going into the fuel rail. I had to on mine. are you sure that your regulator is good? I have alittle different setup on mine. I have a 4.2 with the mopar efi kit on it and im not using a regulator... or at least its not like yours and I havnt found it. look at the pump to see what the output psi is. mine has it stamped on the housing.[/QUOTE]

Yeah I’ve done that as well and I’ve hooked it up bypassing the regulator with no difference unfortunately.
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