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Old 06-13-2009, 12:23 AM   #1
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Post Loosing fuel pressure went sits for awhile

Hey guys

What could cause the fuel pressure to "bleed off" when the Jeep sits for awhile?

Fuel pressure regulator?

Is there some sort of one way valve between fuel pump and fuel rail??

To get it running, I've been "jumping" the connection on the fuel relay to activate the pump manually for a sec ... then it primes up to 30psi and stays that way.

And the next day or so -- its back to 0 psi, even when I turn on the Jeep for the first time. But kicking off the pump for a sec primes it and then it seems to stay working for awhile.




some specs;
1992 Jeep Cherokee Laredo
4.0L 6 cyl - fully rebuilt 2006
new fuel pump 6 months and then 3 weeks ago
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Old 06-13-2009, 12:31 AM   #2
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on mine i had to replace the pump. i am not sure on your year but it may be a check valve in the pump that holds pressure. there are people on here that would know about the pre 96 model better then me. but i say it is the pump
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Old 06-13-2009, 07:19 AM   #3
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Thats right theres a one way check valve in the pump that holds the pressure yours is probably starting to leak and allow for drainback in to the tank causing low pressure youl have to replace the pump to fix it but for the mean time just turn the key on to get the pump running dont start just turn to run do that 3 times and it should fire right up
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Old 06-13-2009, 07:24 AM   #4
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Mine has been losing fuel pressure for about a year now and I use the pump on pump off pump on method. I consider it my anti-theft device. I did find out that the check valve is in the actual fuel pump so if you decide to replace just the fuel pump will suffice.
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Old 06-13-2009, 09:06 AM   #5
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You should be able to turn on the key and wait until the fuel pump builds the pressure before turning the key to the start position. The check ball in the pump is not holding but the pump is fine so the above trick will save having to replace the pump.
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Old 06-13-2009, 12:23 PM   #6
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A inline Check valve could be used...but to be honest the pump is probally weak anyway...and should be changed...
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Old 06-13-2009, 03:18 PM   #7
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Lightbulb

Well, replace the pump again ?!

I paid a local shop to replace it last October - and replaced it again myself last month.

NAPA sold me the last pump -- and I already returned thier plug wire and cap-n-rotor cause it was crap!

Hmm -- so I'll have to check and see if they warranty thier pumps.

Is there like a heavy duty aftermarket replacement for these pumps?

I've already upgraded the ignition use the UID/FIREPOWER 4.0 Kit -- so perfects a better pump would be worth the investment.

Suggestions ?
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Old 06-13-2009, 03:58 PM   #8
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there is a few more test you can do specially for the pre 95.....it involves blocking off the return line to see if the regulator is the cause of the loss of pressure....i was reading the whole process from my hanes manual....might benefit you to pick one up. as it sounds like your problem is elsewhere.
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Old 06-14-2009, 02:31 PM   #9
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Lightbulb fuel pressure regulator

Yeah, I did the tests for the fuel pressure regulator but it was confusing.

the test says to remove the vacuum tube and the fuel pressure should jump up 8-10 psi -- which is does not.

in fact, removing it or leaving it on makes no change.

So perhaps thats the issue -- but I haven't had time to do much more testing yet.
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Old 06-14-2009, 06:41 PM   #10
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before you go through more greif...replace the regulator.
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Old 06-18-2009, 09:14 PM   #11
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Angry now fuel pump is doing nothing at all

I'm waiting for a new fuel pressure regulator to show up in the mail ... but meanwhile I noticed I no longer get pressure even but forcing on the pump.

Now the fuel pump is not working - again!!

This is 3rd pump in 6 months ... I even took the hose off the input end of the fuel filter -- and forced on the pump.

I hear it making noise but no gas is pumping out of the tank.

So - its back to pulling off the stupid tank (which I just filled up) ... and returning the pump to NAPA.

It was a full pump replacement, but wonder if there is something on the assembly that could be causing these pumps to stop working.

It had no fuel pressure last week - but kicking on the pump for a minute seemed to resolve it and it fired right up.
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Old 03-29-2012, 06:34 AM   #12
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I had the same problem with my 2001. Tried the in line check valve idea first. Bought a in line check valve from some guy made for this purpose and it lasted about a week before it essentially disintegrated. Replaced just the fuel pump next, that did not fix it. Replaced the complete fuel pump module next that fixed it for about a month and it started leaking down again. Did the 784 fuel injector swap last night and it held pressure all night and started on the first try this AM. The fuel injector swap is a lot easier than the fuel pump so you might try that first.
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Old 03-29-2012, 09:51 AM   #13
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Mine bleeds down to 10psi almost instantly, then drops to 0 in just a few minutes. So I figure that is a bad check valve too. I was told to watch what brand pump you get, Bosch being the first choice and Carter being second. And then to consider the rest a bad choice. Bosch pumps are big $$ but the Carter pumps can be had on eBay for about $160 and at Rock Auto for $185.
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Old 03-30-2012, 02:41 PM   #14
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I put in the Carter from Rock Auto and have had no problems. The Bosch is big dollars your right. Since I put in the new fuel injectors(784) mine has held pressure and is starting with one key turn. Wow. If you put the new pump assembly in and it still leaks you can do the fuel injector swap for 6 X $24.99. Good upgrade even if doesnt leak.
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Old 04-02-2012, 12:12 AM   #15
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Quote:
Originally Posted by macasylum View Post
I put in the Carter from Rock Auto and have had no problems. The Bosch is big dollars your right. Since I put in the new fuel injectors(784) mine has held pressure and is starting with one key turn. Wow. If you put the new pump assembly in and it still leaks you can do the fuel injector swap for 6 X $24.99. Good upgrade even if doesnt leak.
would you mind telling where you found 4 hole injectors for $25?? Thanks...
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