HELP PLEASE!! random stall & idle issue

ColbyCo

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Hello KJ forum I am hoping your collective knowledge can save me from burning my Libby to the ground.

So I guess I should start from the beginning about 2 months ago completely randomly my KJ stalled out coming out of a parking lot. would start right back up but kept doing it if I was not on the gas. Turned out the IAC had loosened itself out I tightened it back up and the problem disappeared for a week or so then started to stall when coming to a stop. So I replaced the IAC and cleaned the throttle body and everything worked fine for about 10 days then it started up again so I replaced the TPS on a recommedation and the issue still happened. So by now I just didn't feel like playing wack a mole with sensors and took the KJ to a shop to get diagnosed (since I no longer have a full scanner) They looked at it and recommend the cam and crank sensors and said it may be the PCM as their scanner would randomly lose connection. So I replaced the cam and crank sensors and got a reflashed PCM, after doing the cam and crank the KJ ran well and it seemed like it was fixed but 2 days later the issue reemerged on a whim and out of a need for a new one I replaced the gas cap. Now still having the issue some times won't idle after a restart or stall and still no CEL. Any and all recommendations are greatly appreciated the truck is my daily and I do love it but it's slowly killing me at this point.

Thank you all in advance for your knowledge and time

C.
 

LibertyTC

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Welcome to the forums.
What year KJ do you have? The IAC controls the idle, did you install a Mopar or aftermarket one =brand type..?
Have you installed new spark plugs? Do you have the correct spark plugs in the Jeep? USE only NGK ZFR6F-11G (gap them at .040 inch) replace every 35k miles.
Next I'd like to know your fuel pressure test info. Key on psi reading, Jeep running psi, and off for 15 minutes reading.
Try spraying some carb cleaner around the base of throttle body while running. Any change in rpm when you do that?
PCV valve clean & it rattles?
Inspect PCV lines for any potential cracks etc.
 

ColbyCo

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2003 KJ 4X4 RENEGADE, Delphi IAC. Sparkplugs are done every 10-15mile NGK proper gap also replace the PCV and all filters at the same time plugs PCV were last done in May. I will do the throttle body spray test this evening and am waiting for my buddy to bring over his fuel pressure gauge will report back.

thank you
 

ColbyCo

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No vacuum leaks detected with fog and spray test. Did the fuel pressure testing
Key on 50psi peak settle to 45psi
Idle 48—50psi
15 minutes after shut down 45-47psi

But after restart pressure with jump from between 35-45psi rapidly then engine dies.will repeat if trying to idle but will jump up to 50 if revved

Any ideas?
 

ColbyCo

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yes with keyless entry and fog lights. my PCM is 3 blocks if it assets i can supply photos and or video
 

LibertyTC

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You can use the 49.2 psi as standard for the 3 block. I'm still wondering why the jump from between 35-45psi then engine stalls.
It would be recommended to replace the fuel filter first, and then repeat the fuel psi test.
Let me dig into the 03 manual further as well...
 

LibertyTC

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Inspect closely around the gas tank for any cracks in lines/connections etc.
Gas cap should seal properly as well.
The 35 psi is definitely low, it should be consistent. The fuel pressure regulator may be responsible. The regulator is included along with the new fuel pump.
Good news is you do not have to drop the gas tank. Access is though cargo area/ carpet, and read from section 14-1 onwards.
http://www.colorado4wheel.com/manuals/Jeep/KJ/2003JeepKJServiceManual.pdf
I would also replace the external fuel filter as well while there.
 

ColbyCo

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So upon some more tests, I believe the PSI drop is a result of the engine hunting for idle and the alternator surging as all the lights flicker at the same time and once the car dies the psi is rock steady at 49-50psi....... Seems like there might be a problem with the ignition or injector circuit that is dropping off and coming back causing the stall but again that is just a hunch. I don know if anyone else has had this similar behavior, Heard somewhere speed sensor can sometimes cause the issue or similar. Anyone have any other ideas of what to try next.

Thank you LibertyTC for your assistance thus far
 

LibertyTC

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Could this also be an injector issue? I run Chevron Techon Concentrate to help clean the injectors.
If the idle rpm is dropping /stalling, I wonder if it doesn't like the Delphi IAC. Jeep is picky, and possibly a Mopar IAC may be best.
Ensure that the battery & Alt is good, no corrosion to terminals & tight. Get the battery load tested & your alternator bench tested as well.
 

ColbyCo

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So after a year of BS two shops missing it (one being the dealer), I finally figured out *** was going on. The MAP had cracked and as a result, was miss reading. So a $20 dollar part and my KJ is back on the road and back to service.

Thank you all for all the advice.

C.
 

ColbyCo

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The crack was at the base of the connector right above the mounting holes, required removal to see the crack. sadly i don't have the sensor around but I will check if it has been thrown away next time I'm down at my work space.
 
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A warning about $20 MAP sensors. I just installed a rebuilt engine in my 2002 Liberty 3.7; when I did so, I also replaced the MAP sensor with a China made unit from Amazon, because my old one was damaged. Engine ran fine for a week, then it started stalling and loosing power randomly. Wasted a lot of time checking all the other sensors, except the MAP, because it was brand new, but I ended up replacing it with a proper USA made one, and the problem was gone. Engine runs better also and gets better gas mileage.

The lesson here is pay the $100 for a USA made MAP.
 

klc

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From what I’ve read around here, these cars can be quite persnickety about their sensors. I’m grateful there wasn’t much wrong with my car when I bought it.
 

LibertyTC

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OEM/ Mopar sensors for the Jeep is recommended.
Car ? We drive Jeeps !
 

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