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  #1  
Old October 20th, 2005, 09:26
jp's xj jp's xj is offline
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Question 98 Cherokee gas line pressure

I have been having the same problem many others have had with cold starts. Engine turns over for 6-8 seconds then finally starts. Only happens when sits for a long period like overnight. Just changed the fuel filter/regulator and that helped, but still happens intermitantly. Trying to figure out where a possible leak off of pressure could be coming from, changed the gas cap, checked lines. Could this be a leaking fuel injector?? How would I check something like this?? I don't see anything in my manual about a check valve in the fuel sending unit, which is something else I was thinking could be a problem. Any other ideas??
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Old October 20th, 2005, 09:35
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LazarusMJ LazarusMJ is offline
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Re: 98 Cherokee gas line pressure

I haven't seen a 4.0 that hasn't had this problem. In my opinion it is just backfeeding to the tank, like you said. A check valve might fix it but I have learned to live with it. If yours has the vacuum operated fuel pressure regulator like my '88 (not too familiar with newer 4.0s) it will take a while to start after sitting over night because even though the fuel pump pressurizes the line when you turn the key, the fuel rail still needs to be pressurized once vacuum opens the regulator.
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Old October 20th, 2005, 09:38
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Re: 98 Cherokee gas line pressure

You would have to connect a pressure gauge to the test port and see if it's leaking down.
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Old October 20th, 2005, 09:42
jp's xj jp's xj is offline
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Re: 98 Cherokee gas line pressure

How would I determine exactly where it is leaking down??? The pressure gauge will tell me if it is or not, but doesn't say where.
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Old October 20th, 2005, 10:20
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Re: 98 Cherokee gas line pressure

Quote:
Originally Posted by jp's xj
How would I determine exactly where it is leaking down??? The pressure gauge will tell me if it is or not, but doesn't say where.
If it's leaking down then you need to block the line back to the tank to tell where the leak is. Injectors need to be tested one at a time with a hand pump.
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Old October 20th, 2005, 10:31
jp's xj jp's xj is offline
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Re: 98 Cherokee gas line pressure

Sounds like a lot of work, do you know if there is indeed a check valve in the fuel sending unit for this year ? (it has the serviceable fuel filter / regulator on top of the tank) If I pull each injector and test them, do I have to replace all the o-rings?
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Old October 20th, 2005, 10:40
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Re: 98 Cherokee gas line pressure

Quote:
Originally Posted by jp's xj
Sounds like a lot of work, do you know if there is indeed a check valve in the fuel sending unit for this year ? (it has the serviceable fuel filter / regulator on top of the tank) If I pull each injector and test them, do I have to replace all the o-rings?
Every fuel pump has a check valve. Always replace the 0-rings.
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Old October 20th, 2005, 10:59
jp's xj jp's xj is offline
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Re: 98 Cherokee gas line pressure

Do you know If I can replace just the pump itself, or do I have to replace the whole fuel sending unit?
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Old October 20th, 2005, 11:02
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Re: 98 Cherokee gas line pressure

Quote:
Originally Posted by jp's xj
Do you know If I can replace just the pump itself, or do I have to replace the whole fuel sending unit?
You should be able to get either.
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