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Unread 03-04-2014, 10:49 PM   #1
JackTupp
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1995 YJ Wrangler 
 
Join Date: Mar 2014
Location: Tahoe City, Ca
Posts: 12
Getting a high reading on fuel pressure test

I've been having some trouble starting the 95 4.0L. It starts and runs well but I have to pump the gas or hold the pedal down then it just barely starts. So I ran a fuel pressure test on the MPI fuel injection. I received a psi of 48 and no change when I detached the line from the vacuum assisted pressure regulator. The book says to check the return fuel line. I can't determine which is the return line. Is the pressure regular bad?

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Unread 03-05-2014, 05:35 AM   #2
Jeepsr4me
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return lines are always smaller..
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Unread 03-05-2014, 07:29 AM   #3
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,143
The return line comes off the pressure regulator. Disconnect the return line from the regulator. Take a piece of hose and put it on the fuel rail and run it to a gas can. Start and check your pressure again. Then shut it off. If the pressure drops then the issue is the return line and you need to repeat the process by disconnecting it at the tank. If it stays high then the regulator is bad.
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Unread 03-05-2014, 08:23 AM   #4
jsipe007
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1994 YJ Wrangler 
 
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Location: Reno, Nevada
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Que will be able to help you, I had a very similar issue not long ago.

Sounds like fuel pressure isnt staying at the fuel rail in addition to the high fuel pressure. Did you check the pressure after shutting the engine off? pressure should hold at the fuel rail. I dont know the exact specs but they're available online. If it doesn't hold fuel pressure, the fuel pressure regulator is likely bad. Be careful though and don't assume it is only the regulator. High fuel pressure is generally caused by a blocked return line. If you install a good fuel regulator, the high fuel pressure can cause it to fail again.

is your tub in good shape? I only ask because there is a spot in the rear of the jeep where the fuel lines go between the tub and frame. It is a common area to find a pinched return line (unless you have a body lift)
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Unread 03-05-2014, 08:45 AM   #5
JackTupp
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1995 YJ Wrangler 
 
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Location: Tahoe City, Ca
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Quote:
Originally Posted by jsipe007 View Post
Que will be able to help you, I had a very similar issue not long ago.

Sounds like fuel pressure isnt staying at the fuel rail in addition to the high fuel pressure. Did you check the pressure after shutting the engine off? pressure should hold at the fuel rail. I dont know the exact specs but they're available online. If it doesn't hold fuel pressure, the fuel pressure regulator is likely bad. Be careful though and don't assume it is only the regulator. High fuel pressure is generally caused by a blocked return line. If you install a good fuel regulator, the high fuel pressure can cause it to fail again.

is your tub in good shape? I only ask because there is a spot in the rear of the jeep where the fuel lines go between the tub and frame. It is a common area to find a pinched return line (unless you have a body lift)


Thanks for the info. I'll go after the return line. My tub is in good shape and I have a body lift.
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Unread 03-05-2014, 04:16 PM   #6
Mark05059
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1989 YJ Wrangler 
 
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there has also been times when the hoses get pinched when the tank is dropped and reinstalled.
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Unread 03-05-2014, 04:38 PM   #7
Que89YJ
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1989 YJ Wrangler 
 
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The pinched line is why you do it again at the tank if it stays high. If it is normal at the tank fuel line then its the return line in the tank.
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Unread 03-08-2014, 11:10 PM   #8
JackTupp
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1995 YJ Wrangler 
 
Join Date: Mar 2014
Location: Tahoe City, Ca
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Just went through the return line. Chased it all the way to the tank. The return line in the tank had sunk down and was pushed against the bottom of the tank. I cut the return tube down a quarter inch and the supporting washer. runs like a champ.
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Unread 03-08-2014, 11:36 PM   #9
jsipe007
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Sweet! Same exact solution as in my yj.
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Unread 03-09-2014, 06:56 AM   #10
Que89YJ
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1989 YJ Wrangler 
 
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Location: Detroit, Michigan
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It seems to be happening a lot. Glad it is running better.
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