Fuel injectors or fuel pump? - JeepForum.com
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post #1 of 27 Old 05-17-2019, 03:43 PM Thread Starter
xj2000cherokee
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Fuel injectors or fuel pump?

Hello. Looking for assistance on a problem I知 having with my Jeep. It starts right up in the morning without a problem. If I drive it for a while and then turn the engine off (for say 1/2 an hour or so), there is a very long crank time that occurs when I try to restart it. However, if I turn it off and then start it immediately, the engine comes on without a long crank time. If I let the car sit for a while and then prime the fuel pump with the key a few times, the engine starts right up. I知 thinking it is a fuel pump problem and I will need to replace it. However, I know that vapor lock in the injectors might also cause this problem. Looking for input before I go out and buy and replace the fuel pump. Thanks so much in advance.

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post #2 of 27 Old 05-17-2019, 04:42 PM
CJ7-Tim
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2000-01 are very prone to those symptoms. It is called heat soak, and is basically vapor lock at the fuel rail. The fuel pump is OK and does not need to be replaced.

Read this thread >> www.jeepforum.com/forum/f11/hot-start-heat-soak-4352929/

The best cure is to buy an ELK-960 delay timing device for the electric fan and set it to run the e-fan for 4-8 minutes after the engine is shut off. Running the e-fan cools the engine and engine bay enough to reduce or eliminate the heat soak symptoms.

www.elkproducts.com/product-catalog/elk-960-delay-timer-module
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post #3 of 27 Old 05-17-2019, 05:06 PM
jtec
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Do a fuel pressure test, then leaving gauge on and with (KOEO) Key On Engine Off observe pressure drop, drops Xpsi in 5minutes, post results.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 27 Old 05-17-2019, 05:34 PM Thread Starter
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Thanks for replies guys. Had no idea about heat soak. Cj7-Tim: thanks for link to old thread. Great information there. While the fan timer seems to be a great solution, I might start with the fuel injector wrap from Amazon that was mentioned. It seems easier. I値l also look into the fuel pressure test.
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post #5 of 27 Old 05-17-2019, 06:40 PM
jtec
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I am not so sure of heat soak - maybe the temp here at mid 60's Has me second guessing that scenario.

Has the jeep always had this issue?

Maybe check pressures first and put insulators on the shopping list.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 27 Old 05-17-2019, 07:57 PM Thread Starter
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Ok. I値l check pressure first and report back. Just need to purchase a fuel pressure gauge. I値l get one in the morning. So after I attach the gauge to the schrader valve, I just turn the key to the on position and watch the pressure rise and then possibly fall? Or do I run it first, then turn the engine off and then turn the key to the on position to see if it falls?
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post #7 of 27 Old 05-17-2019, 11:03 PM
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Quote:
Originally Posted by xj2000cherokee View Post
Ok. I値l check pressure first and report back. Just need to purchase a fuel pressure gauge. I値l get one in the morning. So after I attach the gauge to the schrader valve, I just turn the key to the on position and watch the pressure rise and then possibly fall? Or do I run it first, then turn the engine off and then turn the key to the on position to see if it falls?
Do several tests.
- Key On Engine Running at idle. Observe & write down fuel pressure.
- Key On Engine Running, power brake the engine (1500-2000 RPM's for afew seconds). Observe & write down fuel pressure.
- Key On Engine Off. Observe & write down fuel pressure every 5 minutes for 30 minutes. You can even leave the gauge hooked up overnight & record what you see.

*****Note, do the power brake last. If your fuel pressure drops off on any of the tests, there is no need to proceed. You will have to determine the reason for the fuel pressure dropping off.

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post #8 of 27 Old 05-18-2019, 06:19 AM
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the last test mentioned above - be sure Key ON engine off, I had to restate that, KEY ON eng off.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 27 Old 05-18-2019, 05:24 PM Thread Starter
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Ok, I picked up an Actron fuel pressure tester today and ran the test. The results are as follows:
1.) With the engine on and at operating temperature, the gauge read a steady 50 psi.
2.) When the engine was turned off, the gauge did not hold pressure. It fell from 50 to about 4 psi very quickly (5-10 sec).
3.) With key on engine off, the gauge rose quickly to 40 psi but then fell down to about 4 psi within 5 to 10 seconds.

Do these results conclude fuel pump or are more tests needed? Leaking injector(s) possibly? Thanks in advance for any input.
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post #10 of 27 Old 05-19-2019, 07:39 AM
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The 1997-2001 fuel pump check valve is supposed to hold pressure in the fuel line while the engine is off. The check valve is located on the fuel pump and located inside the gas tank. Check valve failure is very common. A failed check valve allows fuel to drain back to the tank very quickly after shut down. This results in one or more of the following symptoms:

SYMPTOMS
• Longer than normal cranking times
• Never starts on first try, almost always starts on the second try
• Rough idle for a few moments of idling
• Rough running for first ス block of driving
• Little or no fuel pressure at the fuel rail test valve similar to this -
 
1- Key in on position; fuel pump primes for 2 seconds then stops. 0 PSI
2- Cranking over the engine. 2-3 PSI
3- Engine starts and idles for 20 seconds. < 5 PSI
4- Engine idles and fuel pressure creeps up to 45-50 PSI.
 
 
POSSIBLE CAUSES
• Failed check valve on the fuel pump in the gas tank.
• Leaky fuel injector(s) may be the true cause of your problem, but more likely they are simply contributing to the check valve issue.
 
Testing of the fuel injectors should show if any are faulty and are allowing fuel to drain into the cylinder. Either problem can allow heat soak to vaporize the remaining fuel in the fuel rail, and you may be dealing with a bit of vapor lock as well, especially in warmer weather.
 
1. Connect the gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 psi.
 
2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank. Watch the pressure gage and see how long it takes to loose pressure.
 
If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably one or more leaky injectors.
 
There are a few solutions to the problem –
 
1. Turn the key to ON for 5 seconds and let the fuel pump prime. Turn the key to OFF, turn the key back to ON for 5 seconds, start the engine.
 
2. Crank the engine for 3-5 seconds, pause, and crank the engine again. It will almost always start on the second try.
 
3. Replace the fuel pump assembly in the gas tank. The check valve is not a separate part and cannot be serviced. This is both expensive and time consuming because you have to remove any hitches and skid plates and then remove the gas tank from the vehicle.
 
You can use solutions 1 or 2 for as long as you want to, they do not harm anything and the fuel pump will continue to function for many more years.
 
 
If you do replace the fuel pump assembly, purchase a high quality OEM style pump assembly such as Bosch or Carter. Some cheap aftermarket fuel pump assemblies, like Airtex, and Precision don’t hold up and will fail completely within 12-18 months.
 

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post #11 of 27 Old 05-19-2019, 08:48 AM
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CJ7-Tim is correct. If you replace your injectors, dont forget to upgrade to 4 pintles. Better fuel atomization. Econ, throttle response, etc. I got a set of remans on Amazon for $50. They were perfect. I have 15k on them with no issues.

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post #12 of 27 Old 05-19-2019, 12:37 PM
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Quote:
Originally Posted by CJ7-Tim View Post
 
1. Connect the gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 psi.
 
2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank. Watch the pressure gage and see how long it takes to loose pressure.
 
If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably one or more leaky injectors.
Just be careful with what you clamp the fuel hose with. A pair of Hose Pinch Off Lock Pliers works really good.

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post #13 of 27 Old 05-19-2019, 01:35 PM Thread Starter
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Thanks for the really detailed and informative reply CJ7-Tim. I致e been using the key trick for awhile now and it has been working. At some point I値l get around to replacing the pump and possibly injectors if needed. I値l check out those fuel injectors from Amazon that were mentioned. I壇 like to go with a Bosch fuel pump but have been having trouble finding them. I値l keep looking though. Thanks again to everyone for all of your suggestions and help.
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post #14 of 27 Old 05-21-2019, 05:38 PM
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If the problem turns out to be the fuel pump check valve, you can consider putting a fuel check valve inline. I did that with a generator that had a similar problem.
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post #15 of 27 Old 05-22-2019, 05:19 AM
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Quote:
Originally Posted by xj2000cherokee View Post
Hello. Looking for assistance on a problem I知 having with my Jeep. It starts right up in the morning without a problem. If I drive it for a while and then turn the engine off (for say 1/2 an hour or so), there is a very long crank time that occurs when I try to restart it. However, if I turn it off and then start it immediately, the engine comes on without a long crank time. If I let the car sit for a while and then prime the fuel pump with the key a few times, the engine starts right up. I知 thinking it is a fuel pump problem and I will need to replace it. However, I know that vapor lock in the injectors might also cause this problem. Looking for input before I go out and buy and replace the fuel pump. Thanks so much in advance.
I'm not being Jeep Specific but it might just be a Fuel pump relay getting hot. Can you hear the Pump running when you Prime it? When you turn the Key to Run position you should hear the pump run for a full second and then the relay click off.

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