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Unread 06-27-2014, 08:55 PM   #1
93zjer
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1993 ZJ 
 
Join Date: Jan 2010
Location: Humboldt, California
Posts: 317
Fuel pressure and vacuum question

How much should my fuel pressure and vacuum fluctuate when the jeep is running?
My fuel pressure fluctuates rapidly between 34 and 39 psi at idle.
When I unplug the vacuum line from the regulator the pressure goes to a very stable 39 psi.

My manifold vacuum also rapidly fluctuates between 17 and 20 inHg.

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Unread 06-27-2014, 08:57 PM   #2
93zjer
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1993 ZJ 
 
Join Date: Jan 2010
Location: Humboldt, California
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Yes I bled the gauge.
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Unread 06-27-2014, 09:27 PM   #3
ZeeJay1997
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sounds like you've got something going on with the valves. try some top end cleaner.
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Unread 06-27-2014, 10:38 PM   #4
93zjer
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Join Date: Jan 2010
Location: Humboldt, California
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I just noticed that my fuel pressure instantly drops to zero when I turn off the engine.
I clamped off the return line to see if it the check valve in the fuel pump or the a leaking injector.

Pressure rose to exactly 70 psi before shutting off engine. After 30 minutes it fell to by 19 psi to 51 psi.
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Unread 09-20-2014, 01:34 PM   #5
93zjer
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It was the check valve in the fuel pump for the return line.
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Unread 09-20-2014, 07:49 PM   #6
mikem350
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I bought a universal check valve (for gasoline) 3/8 line size off ebay...might work if you don't want to swap the pump
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Unread 09-21-2014, 01:43 PM   #7
93zjer
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1993 ZJ 
 
Join Date: Jan 2010
Location: Humboldt, California
Posts: 317
Interesting idea. I actually already replaced it, it was lifetime warranty.
I tried in the past to do the swampboy external pump mod but I got a new defective pump (MSD brand via summit). I waited almost a year before I went to install it and found it was defective so now I have a MSD paper weight.
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