Help with Jeep not holding fuel rail pressure - JeepForum.com

 
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post #1 of 10 Old 05-25-2011, 06:41 PM Thread Starter
Suzanna801
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Help with Jeep not holding fuel rail pressure

Hello everyone,

I am hoping to get suggestions or answers for a problem with my 1993 Jeep Grand Cherokee 5.2L. I have been having a problem with the engine not firing unless cranked a few times, we were told by an auto shop that we needed a new fuel pump. My boyfriend dropped the tank and installed a new pump today, but it did not fix the problem.

I have very, very limited funds right now due to having lost my job, so I'm hoping to get some directions on what we can check and hopefully solve this problem ourselves. Any help is greatly appreciated! Thank you.


1993 Jeep Grand Cherokee Limited, 5.2
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post #2 of 10 Old 05-25-2011, 06:56 PM
TallyZJ
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Quote:
Originally Posted by Suzanna801 View Post
Hello everyone,

I am hoping to get suggestions or answers for a problem with my 1993 Jeep Grand Cherokee 5.2L. I have been having a problem with the engine not firing unless cranked a few times, we were told by an auto shop that we needed a new fuel pump. My boyfriend dropped the tank and installed a new pump today, but it did not fix the problem.

I have very, very limited funds right now due to having lost my job, so I'm hoping to get some directions on what we can check and hopefully solve this problem ourselves. Any help is greatly appreciated! Thank you.
This doesn't totally explain your issue. Your title said "Not holding fuel pressure". Your explanation of the issue doesn't mention fuel pressure at all. You just say you have to crank it over a few times before it starts. If the fuel pump itself had been bad it likely would not have started at all.

All Jeeps have to spin over a few times before they crank up and run. This allows the ECU to register all the data it needs then allow spark and fuel to ignite.

Have you physically checked fuel pressure? Does it hold?

Does it eventually crank and run? How does it run? Good bad? Does it run better cold or when hot? Does it crank and start better when cold or after sitting or when still warm from previous running?



If you are not holding fuel pressure at the rail it can only be one or two of a few things.

- Fuel pressure regulator is bad (this is sometimes part of the fuel pump assembly which should have been replaced as a complete assembly, not just a pump module)

- On the fuel rail pressure regulator (this is a bell shaped regulator that is on the fuel rail itself. Check it for gas leaks)

- Injectors are leaking down into the cylinders

- Other fuel system leak somewhere

1996 Jeep Grand Cherokee Laredo 4x4 - 4.0L

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post #3 of 10 Old 05-25-2011, 07:08 PM
Grand_ZJ
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My ZJ didn't hold pressure at the rail either. It would start eventually. The problem was my fuel pump was bad.

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1996 XJ Sport
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post #4 of 10 Old 05-25-2011, 07:28 PM
classicmetalman
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Tr y this:
Next time you try to start, cycle the key to "on" twice and on the third time try to start. Does it fire right up? Do you hear the pump prime for a couple of seconds each time? Should.
Check your fuel pressure. Rent a gauge from the parts store ($ back on return) Running, pressure should be around 40PSI. Leave gauge hooked up and shut down Jeep. Let it cool down, there shouldn't be a significant loss in pressure. If there is, as mentioned earlier, you could have a couple of possibilities. Leaky injector or bad regulator being a few.
Leaking injector: pull the plugs and check their condition. Is it running rough? Could have a fouled plug because of leak.
If all the plugs look decent, could be a bad regulator. IIRC, yours should be on the rail.
Have you checked for an actual leak? Post back with your findings
HTH

Robert
93 Laredo 4.0
96 Limited 4.0

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I say you should still hit something just to let it know you mean business, or shake a hammer at it in a menacing fashion
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post #5 of 10 Old 05-25-2011, 07:29 PM Thread Starter
Suzanna801
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Well, I am not a mechanic so I apologize that my wording was incorrect.

I was told by the auto shop that it was not holding fuel pressure and that I needed a new fuel pump. He did not mention a specific number for the pressure. A few months back we were having some roughness issues and in the process of diagnosing that we did check the pressure ourselves and it read slightly lower than what the specs said it should be at; I do not remember the exact numbers.

I have owned this Jeep for about 6 years now, and it has never taken more than a couple of seconds to fire up. Now I have to crank the key 2 to 3 times for 4 or 5 seconds each time before it fires. Once started it runs just fine, smooth and no hesitations. When I go to the store for a few items, it usually has a slight cranking issue again, but not as pronounced as after it sit for hours.

We have replaced the fuel regulator and the filter as well, before we replaced the fuel pump. If there is any other information you may need, I'll do my best to post it. I need suggestions, and possibly explanations, of what and/or how to check things that may cause this issue.

1993 Jeep Grand Cherokee Limited, 5.2
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post #6 of 10 Old 05-25-2011, 07:32 PM Thread Starter
Suzanna801
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Thank you Robert! You posted as I was replying so I didn't see it until now. We will check these things and report back!

1993 Jeep Grand Cherokee Limited, 5.2
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post #7 of 10 Old 05-25-2011, 07:41 PM
classicmetalman
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Quote:
Originally Posted by Suzanna801 View Post
Thank you Robert! You posted as I was replying so I didn't see it until now. We will check these things and report back!
Your welcome

Quote:
Originally Posted by Suzanna801 View Post
I have owned this Jeep for about 6 years now, and it has never taken more than a couple of seconds to fire up. Now I have to crank the key 2 to 3 times for 4 or 5 seconds each time before it fires. Once started it runs just fine, smooth and no hesitations. When I go to the store for a few items, it usually has a slight cranking issue again, but not as pronounced as after it sit for hours.
Yea, sure sounds like your losing pressure. Get the gauge and check to verify. Heck, look for a leak first, FREE n EZ!

Robert
93 Laredo 4.0
96 Limited 4.0

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I say you should still hit something just to let it know you mean business, or shake a hammer at it in a menacing fashion
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post #8 of 10 Old 05-25-2011, 08:32 PM
TallyZJ
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Quote:
Originally Posted by Suzanna801 View Post
Well, I am not a mechanic so I apologize that my wording was incorrect.

I was told by the auto shop that it was not holding fuel pressure and that I needed a new fuel pump. He did not mention a specific number for the pressure. A few months back we were having some roughness issues and in the process of diagnosing that we did check the pressure ourselves and it read slightly lower than what the specs said it should be at; I do not remember the exact numbers.

I have owned this Jeep for about 6 years now, and it has never taken more than a couple of seconds to fire up. Now I have to crank the key 2 to 3 times for 4 or 5 seconds each time before it fires. Once started it runs just fine, smooth and no hesitations. When I go to the store for a few items, it usually has a slight cranking issue again, but not as pronounced as after it sit for hours.

We have replaced the fuel regulator and the filter as well, before we replaced the fuel pump. If there is any other information you may need, I'll do my best to post it. I need suggestions, and possibly explanations, of what and/or how to check things that may cause this issue.
No need to apologize. It is just that diagnosis is hard enough through the internet forums and is especially hard without a lot of details.

Sure sounds like the fuel pressure regulator is not letting pressure hold after it is shut down.

I would ask if you know what brand pump was installed? Was it just the pump or did he replace the entire assembly? If he used an Airtex brand pump or assembly then I am afraid you will likely be doing it all over again. Airtex is junk!


I recommend AC Delco replacement pump and do the entire assembly at once. It is more money but is well worth it in the long run.

1996 Jeep Grand Cherokee Laredo 4x4 - 4.0L

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post #9 of 10 Old 05-26-2011, 08:56 AM
HighLonesome
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You will lose pressure over time from sitting. That's why the system primes at startup.
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post #10 of 10 Old 05-26-2011, 02:44 PM
ratmonkey
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Quote:
Originally Posted by TallyZJ View Post
This doesn't totally explain your issue. Your title said "Not holding fuel pressure". Your explanation of the issue doesn't mention fuel pressure at all. You just say you have to crank it over a few times before it starts. If the fuel pump itself had been bad it likely would not have started at all.
that is the symptom of not holding static fuel pressure when not running. the cause is a bad check valve in the fuel pump assembly. the assembly should be replaced as a whole and not just the pump portion.
easy check for the reg is to remove the vac line and check the pressure at idle.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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