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Old 01-14-2011, 11:17 PM   #1
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Default 99 Cherokee Fuel pressure.

Ok, I have viewed this forum looking for answers, but so far haven't seen this issue. Here's a lil background.
I have a 1999 Jeep Cherokee Sport. It's 2WD with a 4.0 Liter L6. About a month ago it started to have issues with starting and running. I checked the basics and found my fuel rail to have little, if any, pressure. I checked a few things and ended up replacing the fuel filter/pressure regulator. The problem disappeared for about a week. So this told me to replace the pump itself and screens in the tank. Yesterday I put a new fuel pump and both in tank screens. The issue is still there. I disconnected the feed line from the tank and the fuel rail and blew compressed air through it. No clog was detected. I have checked all the fittings and connections and there is no external fuel leak. The truck has long crank times whether it sits 2 hours or 5 min. If I "prime" the ignition a few times(Key on and off but not cranking motor) the truck will fire right up. Once running, the truck runs great. So I can't figure out where I could possibly be losing my fuel pressure too. With the repairs made it "shouldn't" be going back into the tank. Where else could it possibly go, and what checks can I do to verify. I have already invested several hours and over $250 and I'm trying to avoid another $300. The $300 would be a set of 6 new injectors for the truck to make sure they aren't leaking.

So just to recap, truck loses fuel pressure after sitting short periods of time.
New fuel pump.
New in tank fuel strainers(both for pump and module)
New Fuel filter/pressure regulator.
Supply line is clear.
No external leaks.

Greatly appreciate and and all help available.
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Old 01-14-2011, 11:35 PM   #2
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if you have a milti meter check your power suply to your fuel pump and make sure you got the right pump for your truck.
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Old 01-14-2011, 11:43 PM   #3
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Might be a leaky injector.
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Old 01-14-2011, 11:44 PM   #4
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Quote:
Originally Posted by TbDk View Post
Ok, I have viewed this forum looking for answers, but so far haven't seen this issue. Here's a lil background.
I have a 1999 Jeep Cherokee Sport. It's 2WD with a 4.0 Liter L6. About a month ago it started to have issues with starting and running. I checked the basics and found my fuel rail to have little, if any, pressure. I checked a few things and ended up replacing the fuel filter/pressure regulator. The problem disappeared for about a week. So this told me to replace the pump itself and screens in the tank. Yesterday I put a new fuel pump and both in tank screens. The issue is still there. I disconnected the feed line from the tank and the fuel rail and blew compressed air through it. No clog was detected. I have checked all the fittings and connections and there is no external fuel leak. The truck has long crank times whether it sits 2 hours or 5 min. If I "prime" the ignition a few times(Key on and off but not cranking motor) the truck will fire right up. Once running, the truck runs great. So I can't figure out where I could possibly be losing my fuel pressure too. With the repairs made it "shouldn't" be going back into the tank. Where else could it possibly go, and what checks can I do to verify. I have already invested several hours and over $250 and I'm trying to avoid another $300. The $300 would be a set of 6 new injectors for the truck to make sure they aren't leaking.

So just to recap, truck loses fuel pressure after sitting short periods of time.
New fuel pump.
New in tank fuel strainers(both for pump and module)
New Fuel filter/pressure regulator.
Supply line is clear.
No external leaks.

Greatly appreciate and and all help available.
Make sure you have the right pump first off. Even if it is new it can still be bad. Losing the prime on your fuel pump is a good indication of a faulty pump. It's also a sign of a possible leak. Remember the fuel tank is under pressure with the gas cap on, so replacing your gas cap is not out of the ordinary either. Start by checking for leaks, replace cap, and if it's not solved, pump and gasket/o-ring on tank. let us know how you make out.
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Old 01-14-2011, 11:50 PM   #5
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hey man .... pre 97 jeeps were notorious for bad fuel tanks that eroded from the inside and caused havoc to your fuel system .... if you know your battery is good to go, then i would suggest drain and drop the fuel tank and have it cleaned/boiled really well - if it's bad, replace it ..... bad tank will cause fuel system headaches and strand you! ....good luck!
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Old 01-14-2011, 11:51 PM   #6
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^ x2
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Old 01-15-2011, 05:40 AM   #7
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With a fuel pressure gauge, the proper adapters, and an FSM that outlines the pressure leakdown test procedure and specs, you should be able to isolate this.

The real key here is that many gauges have adapters that allow you to "crimp off" or stop the fuel pressure right near the gauge.

With the fuel pressure crimped off, you can isolate whether the drop is coming from either the tank side or the fuel rail / injector side.
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Old 01-16-2011, 08:49 AM   #8
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Quote:
Originally Posted by kbad View Post
hey man .... pre 97 jeeps were notorious for bad fuel tanks that eroded from the inside and caused havoc to your fuel system .... if you know your battery is good to go, then i would suggest drain and drop the fuel tank and have it cleaned/boiled really well - if it's bad, replace it ..... bad tank will cause fuel system headaches and strand you! ....good luck!
This is for a 99.
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Old 01-17-2011, 08:19 AM   #9
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I took the fuel pump back out and back to the store for a swap. Installed the new pump and everything seems to be good now.

The jeep is starting like it's supposed to so far. I will update again and let you guys know if the issue returns, but so far this is possibly solved.
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Old 01-17-2011, 08:30 AM   #10
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Originally Posted by TbDk View Post
I took the fuel pump back out and back to the store for a swap. Installed the new pump and everything seems to be good now.

The jeep is starting like it's supposed to so far. I will update again and let you guys know if the issue returns, but so far this is possibly solved.
glad to hear it. Gotta love aftermarket junk parts.
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