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Old 03-25-2012, 10:49 AM   #1
dsmithwc04's Avatar
Join Date: Mar 2012
Posts: 57
Can't diagnose fuel pressure problem

Hello all, just bought a 93 wrangler 2.5 that was not running when I bought it. I diagnosed it as a fuel pressure problem since the fuel rail had 0 psi. Once home I have tried further to diagnose the exact cause of the problem and with no luck so hopefully somebody can help me out. Here is a breakdown of the problem.

1. Fuel pump does turn on for a couple seconds with ignition.

2. Reads 0 psi at fuel rail.

3. Fuel filter was just installed prior to my purchase of the jeep. ANd is installed correctly for proper flow direction.

4. I disconnected the line between the tank and filter and blew compressed air through the fuel supply line with the fuel lines disconnected at the fuel rail and it had no problem moving air through the system.

5. With the tank still disconnected from the filter I turned the iginition on again and some fuel is being pushed through the lines by the pump. Not sure how much flow I should have but I would say it is close to a sink faucet at 1/3 to 1/2 power.

So, could this be a relay turning the pump off prematurely from possibly unbled fuel lines? Do I have to bleed the fuel lines and if so how? The filter doesn't seam to be clogged nor does the line from the filter to the fuel rail. I did a search but couldn't find this particular problem. Any help is extremely appreciated.


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Old 03-25-2012, 11:44 AM   #2
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A mpi system is high Pressure. If the pump is working it should have been spraying the fuel out of the hose. Hanes states that fuel pressure at idle should be 31psi with vacuum and 39psi without vacuum.

Based on what you said I would think the fuel pump is bad.

Hanes has a thorough looking test, but requires the vehicle to be started and running at idle.
Hanes states If pressure is not within specification. [31 with vacuum, 39 without vacuum] that one of the following problems exist.

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Old 03-25-2012, 02:26 PM   #3
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Old 03-25-2012, 02:37 PM   #4
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That does seem a decent amount of fuel. You said you blew compressed air through all the lines, might be worth is to check the fuel pressure regulator. It the next possible failure point when it comes to fuel pressure.
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Old 03-25-2012, 07:50 PM   #5
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Location: Central Alabama
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could also be the in tank fuel filter on the end of the pump.....that get's clogged and you ain't get'n no fuel, period....
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Old 03-26-2012, 09:26 AM   #6
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Well, ended up an easy fix. I decided to unhook the fuel lines at the fuel rail and reconnect all other lines. Attempted to start until fuel began to run out fuel line. I was suprised any fuel came out since it had zero pressure when i tested it. I then reconnected the fuel line and tried to start it and it started right up. Didnt know fuel lines need bled when mostly empty. Its not registered yet so i only drove it in my neighborhood for about a minute but no fuel problems that i see. Thanks for everyones help and hopes this might helps somebody else out. Next issue is a burnt smell coming from the engine bay. Smells like oil and since the valve cover is seaping oil from everywhich direction i wonder if thats the culprit. Time for a valve cover replacement i guess. Any thing in particular i should watch out for or pretty much standard valve cover gasket replacement?
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Old 03-26-2012, 03:02 PM   #7
Join Date: Jan 2010
Location: Las Cruces, NM
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Not sure on your valve cover , but on mine which is the aluminum one, there is no gasket but you use black RTV, if yours is like that, lay a decent bead on the clean cover, (3/8"), let it set for a few minutes for it to start to set up. Its sort of tough to get the back of the cover on without messing up the RTV>>

(Sold)1994 Jeep Wrangler 2.5L, Bestop top
/w steel half door and slider windows
5 speed, 2.5" lift, 31" tires,rack lights
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