2002 4.0 Hard-Start - Fuel Pump - Fuel Injector - PCM - JeepForum.com
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post #1 of 13 Old 06-28-2019, 08:05 AM Thread Starter
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2002 4.0 Hard-Start - Fuel Pump - Fuel Injector - PCM

I purchased my 2002 X about 2 years ago and it only had 30K miles on it. I was told the previous owner would leave it parked at his hunting camp for long periods. After I bought it, I changed all fluids, plugs, and general maintenance items and it is in great condition. About 6 months ago, I had some hard starting issues and after reading some nice posts here, I diagnosed my problem as a bad valve on my fuel pump. I tried to purchase a Bosch but I couldn't find one anywhere. The best quality available at the time seemed to be the NAPA one. The replacement went well and it immediately fixed that issue. I no longer needed to turn the key on/off 3-5 times to prime the pump in the morning. After a couple of days, the starting issues returned but it was different. A cold start seemed to have too much fuel. Hot starts became more difficult as well. Again back to the forum and I found the TSB for heat-soak issue.

I purchased the white cylindrical insulators recommended by the TSB and they have had some effect. Convinced this was my problem, I purchased the DEI Kit and will replace the heat shield with the DEI one which is thicker, the fuel rail sleeve, and the injector wraps.

Yesterday, after wrapping just the #3 injector with the insulation, I was surprised that I didn't see a more significant hot-start improvement. Also my morning cold start still wasn't great and it seemed to take about 3-4 seconds to fire up and chugs as if too rich. After it starts, runs great and has since the first day I bought it.

I have come up with a theory of what is happening and I would appreciate constructive input. After reading tons of posts here and other places, I'm thinking that the new fuel pump and valve that now keeps fuel pressure constant has revealed a leaky fuel injector. Anther guy had similar issues to mine and replacing the injectors did the trick. I have ordered some Bosch re-manufactured injectors and plan to install them this weekend along with the full DEI kit. For $100.00 it seems worth it to try it out. I will send an update Sunday evening hopefully with positive news.

Lastly, I have seen others flash or reset the PCM after installing new injectors. Is this required for it to relearn? The service manual didn't mention the reset as a requirement after replacement and I didn't know if the 2002 4.0 was any different.

I do apologize for all the detail but I wanted to provide as much information up front. Also, this has been frustrating and hopefully my issue and your responses can help the next person with a similar issue.

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post #2 of 13 Old 06-28-2019, 11:18 PM
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If you suspect one or more injectors are leaking, hook up a pressure gauge to the fuel rail, switch the ignition on and verify pressure rises to 49psi +/-5psi, start the engine and verify operating pressure is still in spec, then turn the ignition off and wait five minutes -- with a good check valve and injectors the pressure should not drop below 30psi.

Clearing the adaptive memory in the PCM shouldn't be necessary after changing the injectors, but it couldn't hurt. To do so, use the following procedure:
  • Disconnect the positive battery cable terminal and touch it to ground for 30 seconds
  • Reconnect the Battery Cable
  • Switch the ignition ON but do not start the engine
  • Turn Headlights ON then OFF
  • Switch the ignition OFF

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post #3 of 13 Old 07-11-2019, 03:24 PM Thread Starter
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I installed the new fuel injectors and my morning start is much better and very quick. After looking at the original ones i removed, it seemed debris had gone past the o-ring so I assume some fuel was leaking through as well.

I also installed the DEI kit which included a new heat shield above the intake manifold, complete wrap on the fuel rain and individual wraps for each injector. The problem is that I am still having an issue with a hot-start. It usually takes 2-3 turns of the key and sputters for a second and then assumes normal idle.

Any suggestions on what to try next? Seems like heat soak still but now I don't know. I have kind of ruled out IAC or TPS sensor since my cold start is fine, Jeep drive great, and I have no issues in the morning.
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post #4 of 13 Old 07-14-2019, 09:49 AM Thread Starter
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Well the improved cold start is back to being labored and takes 2 or 3 seconds then runs fine. Hot start still takes 2 or 3 turns of the key.

Spark plugs are only a year old Autolites. Any recommendations on where to go from here would be appreciated. I will probably try to clean the IAC. Any chance sensors could be the problem ? Which one if so?
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post #5 of 13 Old 07-14-2019, 09:59 AM
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as mukluk mentioned the fuel pressure test - to simple to ignore, BUT after checking running PSI, turn engine off but leave KEY in run/on position this will have the injectors powered with 12v.

Also ECT - if the PCM see's a bad skewed temp it adjust fuel accordingly.

And let us know after cleaning the IAC.

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 13 Old 07-14-2019, 11:40 AM Thread Starter
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It was good advice to check the fuel pressure...I just didnt want to believe my money and effort on replacing the pump in March was in vain.

Pressure running was @ 32 and as soon as I moved the key from run to start, pressure went to zero.
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post #7 of 13 Old 07-15-2019, 12:50 PM Thread Starter
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Is there anything else I should check prior to replacing the fuel pump assembly again? The brand I used in March was Delphi because I couldn't find a Bosch. Hopefully the Bosch are available again.
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post #8 of 13 Old 07-15-2019, 01:19 PM
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Only check that comes to mind would be to verify the pump is getting a good quality ground and 12v back at the connector near the tank skid. Ground is at pin 6 (BK wire), and power comes in at pin 1 (DG/WT wire) when the pump relay is on or you jumper the socket terminals 30 to 87.

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post #9 of 13 Old 07-28-2019, 08:04 AM Thread Starter
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Ok, I finally have time to work on the TJ but being a novice when it comes to electrical issues, it is not clear to me which tabs on this relay I need to jump to keep the fuel pump running on order to test the tank wires. I would appreciate any assistance.
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post #10 of 13 Old 07-28-2019, 09:11 AM Thread Starter
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I didn't think I was jumping the relay correctly because i couldn't hear the pump come on. Now I got it. Still working....
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post #11 of 13 Old 07-28-2019, 09:18 AM
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fused jumper 9 to 10
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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 #12 of 13 Old 07-28-2019, 09:24 AM Thread Starter
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Thanks, just confirmed ground and power are good at the connection near the tank. Looks like I'm replacing the Delphi fuel pump module I just installed.
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post #13 of 13 Old 07-28-2019, 04:05 PM Thread Starter
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Just to close the loop. Install of the Delphi unit was successful and the TJ starts perfectly.

The red locking tab on the electrical connection near the tank was broken....now i need to research on how to replace that.

Thanks mukluk and others for your comments.
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