TJ won't run after sitting for a long time

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Bobsuruncle

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Norman, OK, USA
Sorry if this has been addressed but I haven’t found an answer yet.

Hello, Leo here. New to the forum but have read all I could find on the issue but it hasn't helped. So here we go. I purchased a nonrunning TJ with 4.0 manual xmission. Previous owner stated it started to idle poorly, after awhile it quit running and has sat for a long time. Don't know how long.
Battery good, grounds to body and block good, fuses and relays in engine power distribution center good, engine cranks over good, 145 to 150psi on all six cylinders, 47 psi at fuel rail. Old coil rail sparked on 1-6, and 2-5 but 3-4 did not. Replaced coil with new MOPAR coil. same 3-4 no spark. Ignition coil driver in PCM out? Possible, but why won't the rest fire off? Fuel injectors 1 thru 6 check with noid light and pulsing. Both fuel injectors and coil get power through ASD relay and fuse 28 so power is good. Two coil packs are firing so crank position sensor is working... Any suggestions? Yes, good fuel with seafoam in tank. New plugs as well. Has darn SKIM but no key light flashing. Thank you!
 
Are you using the skim key? I accidentally used the wrong key on my ram ID it did the same thing, crank but not fire.

Id think even with the center 2 not sparking it would try and run (although badly) on 4 cylinders. I'd check the FSM for a wireing diagram on the coil pack though and still spend some time troubleshooting that. It may be a corroded wire.

—
There must have been a time
when we could have said no.
 
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Thanks, I have no idea on the key. I’m using the only one that came with the Jeep. I get a single flash on the SKIM indicator in the instrument cluster but no flashing red key upon cranking. I am assuming it is ok. I have checked the wires going from the coil to pcm and have continuity. I’ll check them for a short to ground tonight. The coil driver in the pcm removes the ground from the coil pack allowing the magnetic field to collapse and give the spark. So if it is continuously grounded no spark. I’ll check for corrosion as well.
 
I don't think this could be a SKIM problem. A SKIM key problem would only allow the Jeep to run for maybe 2-3 seconds then die.

Does the Jeep stay running or does it not even start? If it runs on the 4 working cylinders and you're sure the one coil pack isn't firing, I would look in the FSM and trace the wires from the PCM to the coil rail. If all the wires are good I was suspect a bad PCM.
 
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Bobsuruncle said:
Bluedriver scanner is on the way. No codes when I turn ignition on three times for codes.
Click to expand...
The codes don't appear immediately after the third on-off-on of the key, you have to give it some time for the diagnostic routine to complete before they begin appearing. If you do the key sequence right you will always at least see a 'DONE' message in the odometer display even if there are no stored codes. The only model years this doesn't work on are 98-99 and possibly early 00 models.

With everything that has been done, make sure the IAC and the orifice in the throttle body its plunger fits into are clean. A dirty IAC can cause a poor idle or inability to idle. The TPS can also cause a bad idle as can a bad upstream O2 sensor.
 
Yep doesn't sound like a skim problem then.

I assume you have tried cranking it while giving a bit of throttle? That would eliminate a plugged IAC as the issue. I remember reading a long time ago about a possible corrosion location inside the ecm plugs. Apparently the plugs can be split appart and corrosion can hide inside. I've never checked mine to verify this it's just something I tripped over online years ago. It's another place to look though.

—
There must have been a time
when we could have said no.
 
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Jerry Bransford said:
The codes don't appear immediately after the third on-off-on of the key, you have to give it some time for the diagnostic routine to complete before they begin appearing. If you do the key sequence right you will always at least see a 'DONE' message in the odometer display even if there are no stored codes. The only model years this doesn't work on are 98-99 and possibly early 00 models.

With everything that has been done, make sure the IAC and the orifice in the throttle body its plunger fits into are clean. A dirty IAC can cause a poor idle or inability to idle. The TPS can also cause a bad idle as can a bad upstream O2 sensor.
Click to expand...
Thanks Jerry, I do get the done message. I’m getting a live data reader so I can see if the sensors are all working. I would think if it was the IAC it would still run but badly. But I am scratching my head and it won’t hurt to clean it. Thanks.
 
Drizit said:
Yep doesn't sound like a skim problem then.

I assume you have tried cranking it while giving a bit of throttle? That would eliminate a plugged IAC as the issue. I remember reading a long time ago about a possible corrosion location inside the ecm plugs. Apparently the plugs can be split appart and corrosion can hide inside. I've never checked mine to verify this it's just something I tripped over online years ago. It's another place to look though.

—
There must have been a time
when we could have said no.
Click to expand...
I’ve tried full throttle, no throttle, pumping throttle... good tip on the connectors. I’ll pull them apart this weekend. Thanks
 
Bobsuruncle said:
Thanks Jerry, I do get the done message. I’m getting a live data reader so I can see if the sensors are all working. I would think if it was the IAC it would still run but badly. But I am scratching my head and it won’t hurt to clean it. Thanks.
Click to expand...
True it would run but only if you held the throttle open slightly with the gas pedal. Same with starting... it wouldn't start unless you held the throttle open when the IAC isn't working properly. Not that I think it's causing it not to start but one of the problems it had before it stopped starting was a bad idle. The big mystery is it not getting spark on two of the cylinders even after already having replaced the coil rail. :)
 
Who knows, perhaps the ecm is doing something to prevent the engine from running due to not getting signal on that wire.

—
There must have been a time
when we could have said no.
 
Bobsuruncle said:
One step closer to solving the mystery... Wire 4 from coil to PCM #3 coil driver open. After tearing 80% of the wire harness apart I found the break. I'll work on it this weekend. Maybe...maybe there is hope. At least this solves the coil not firing on 3-4 cylinders. But still....
Click to expand...
Can you see what caused the wire to break? Rubbing somewhere?
 
I know reading this thread that we are missing spark in 2 cylinders. (now 1?) But nobody brought up the fact that he only has fuel at 47 psi at the rail. I checked mine a few weeks ago on an unrelated issue and mine is a solid 60.

Will a TJ run on low fuel pressure?

I guess it probably would, it would just die like the skim issue.

Sounds like you have some electrical issues that need chasing down.
 
ac_ said:
I know reading this thread that we are missing spark in 2 cylinders. (now 1?) But nobody brought up the fact that he only has fuel at 47 psi at the rail. I checked mine a few weeks ago on an unrelated issue and mine is a solid 60.

Will a TJ run on low fuel pressure?
Click to expand...
49 +/- 2 psi is correct for 97 to 04 TJs. 58 psi +/- 2 psi is correct for 05-06 models.
 
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