Fuel pressure leaking down after shut off - JeepForum.com
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post #1 of 6 Old 07-22-2013, 10:01 AM Thread Starter
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2000 XJ Cherokee 
Join Date: May 2011
Location: Albuquerque
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Fuel pressure leaking down after shut off

1994 ZJ, 4.0L, 5 speed manual. This is my son's car and he has had it two years now. Since the day we got the vehicle it has taken several seconds to start. Always starts, runs great, but has always been a little frustrating. The fuel pressure is right at 32 lbs. but leaks down within 15 seconds after shutting the engine down. I am not one to throw parts at a car but this weekend we dropped the tank and replaced the fuel pump with the Bosch unit. We also replaced the fuel pressure regulator. Neither of these fixed the problem. I hate when that happens! Where is the fuel pressure leaking down. There is no sign of leaking injectors. The jeep idles smooth, has plenty of power, doesn't smoke at start up, doesn't smell of fuel. No signs of a leaky injector.

Could it be the plastic fuel lines? They have the original plastic clips and do not leak fuel, but they could be allowing air in the lines when there is not pressure. Is this something I should look at or is it obviously an injector because that is the only place it could be leaking down?

Just so you know the long story, this is the second pump we put in. We put a Airtex pump in last weekend and it pumped fine except the fuel gauge would not work, so we got the bosch pump. Neither pump took care of the leaking pressure problem.

87yjrad is offline  
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post #2 of 6 Old 07-22-2013, 11:02 AM
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1994 ZJ 
Join Date: Sep 2007
Location: Bloomington
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Sounds like a bad fuel pump/regulator. They come as a whole unit, don't buy a cheap one, they don't last. Stay away from the Airtex ones (my dad went through 3 of them in 8 months). Bosch makes a good fuel pump though (around $200).

chetzar is offline  
post #3 of 6 Old 07-22-2013, 12:09 PM
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1998 ZJ 
Join Date: Feb 2012
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Do you by any chance get a check engine light that shows a misfire on a cylinder My 97 did the same thing, I had 1 bad injector that would stick open occasionally. I fixed it the easy way, I totalled it in an accident and bought another......
But, I agree with chetzar, sounds like a bad check valve in the pump.
V65Ozzie is offline  
post #4 of 6 Old 07-22-2013, 12:23 PM Thread Starter
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I just installed the Bosch pump. I really have a hard time believing 3 different pumps have the same problem.
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post #5 of 6 Old 07-22-2013, 01:32 PM
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1993 ZJ 
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My money is on a leaky injector. I know you said it doesn't smoke at startup but I've sprayed carb cleaner in the intake to clean it out and never noticed smoke on startup. Pretty easy to check too.

Take off the throttle cable bracket. Loosen the fuel rail but leave the injectors attached. Support the fuel rail with the injectors pointing down. Turn the key to run and off a few times to pressurize the system. You can also pull the coil connector and have someone crank the engine to watch the injectors fire. Be careful not to have any sparks though.

I also once had a fuel pressure tester with a button to bleed off fuel pressure. The button bled into a piece of clear hose. I spent a long time trying to find a small leak in my fuel system that turned out to be that bleed button leaking into the hose. My system was fine the whole time.
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post #6 of 6 Old 07-22-2013, 02:26 PM Thread Starter
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2000 XJ Cherokee 
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Cool, I will try that next and report back. I have read the entire leak down test instructions but it takes two separate special adapter tools. Hopefully I can figure it out without having to find those tools.
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