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Unread 09-06-2010, 09:38 PM   #1
jdk3034
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Join Date: Nov 2005
Location: Pittsburgh
Posts: 280
no power to fuel pump

Well I have a 94 Grand Cherokee 5.2L and ran really rough then stalled. Threw a fuel pressure gauge on it and had 0 psi. Got it home, tested for power at the fuel pump connector right before the tank and have no power going through the orange/black power wire. Traced that wire all the way up to the driver's kick panel and no power there. Tried swapping the fog light relay with fuel pump relay and asd relay with abs relay and still no power. I have power at terminal 30 of fuel pump relay in the power distribution center with the ignition off. With ignition on I have power at terminals 30, 85, and 86. Does the PCM provide grounds for the fuel pump relay and asd relay when the ignition is turned on? I'm not exactly sure what to do next, I need to get the damn thing back on the road tho.

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Unread 09-07-2010, 02:02 AM   #2
iPlay1515
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1993 ZJ 
 
Join Date: Jun 2006
Location: Southern Pines NC USA
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I don't have a 95 manual, but on a 93, the PCM does control the fuel pump relay by grounding the coil to close it on pin 51 of the PCM. The auto shutdown relay is controlled by the same circuit.
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Unread 09-07-2010, 11:46 AM   #3
jdk3034
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well turns out there is power to the fuel pump only for about a second or less when i first turn the key on, so i dropped the tank and am changing the pump assy
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Unread 09-08-2010, 03:37 AM   #4
jeepheller98
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when you do it, get new gas tank straps, and good luck with the large fuel pump ring that holds the pump down.. best way to get it off is to tr and spray some lubricant so it gets near the threads and use a WIDE screwdriver and a hammer.
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Unread 09-08-2010, 05:33 AM   #5
iPlay1515
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1993 ZJ 
 
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Location: Southern Pines NC USA
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Quote:
Originally Posted by jdk3034 View Post
well turns out there is power to the fuel pump only for about a second or less when i first turn the key on, so i dropped the tank and am changing the pump assy

If the power to your fuel pump is only there for a second or less, the fuel pump itself may not be your problem. On my 93, when I first turn on the ignition, I can hear the fuel pump run for several seconds and then it stops if I haven't engaged the starter.

The PCM does not monitor or control fuel pressure directly. It relies on a fixed time for the pump to run long enough to build enough pressure to start the engine.

A few years ago, I had a problem with a significant delay with the fuel pump not operating after I turned the ignition switch on. I had to replace the PCM to correct the problem.
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