04 4.0 TJ starting issue

[broganobrien]

Been battling a starting issue for about a year now. (2004, 4.0L Jeep Wrangler Unlimited with 42RLE, no significant mods passed tires, 160k kms/100k mi) Have scoured forums, youtube, you name it, and did hours of troubleshooting and going to send the bobber out into this forum for some advice.

Started after I replaced spark plugs (with NGK OEM replacements). Changed those out as preventative maintenance, and the Champions that were installed were very worn. Initially gapped the replacements to .040, later to .035 to try and solve this issue.

For context, this happens very intermittently, sometimes leaving it overnight it will start perfectly fine, no long crank, no problems at all. Then sometimes when sat overnight it will do the following to some degree. But it almost always will do the following when hot, or warm from being shutdown over at most a few hours.

When starting;

• Engine turns over/starter engages strong, starter seemed (and still seems) fine
• The engine will "catch" (I'm unsure of another term to use here) but will stumble/hesitate and stall out turning itself off. Sometimes it'll catch "stronger" than others, but almost always will stall
  • After sitting overnight, sometimes it will crank, start up, have a DEEP chug/hesitation into the low RPM danger zone for a split second, then you'll feel the engine jump around, but will come back to life. When this happens I don't have to press the gas. Other times when sitting overnight/several days it starts right up with no stumble.
• Starting when warm/hot while pressing the gas will always start it. And because it's been doing it for so long, I'm sometimes able to start it, wait a split second for the stumble, and lightly tap the accelerator to pull RPMs up and keep it alive.
• I can turn off the engine, and try to start it immediately with the exact same problem persisting, can be 2 seconds, or 2 hours. If the gauge is showing anything off the bottom peg I'd put money on; start, tries to catch, stumbles, dies
  • For context, the last 3 events happen before the starter stops free-wheeling when it's disengaged. Too quick to be SKIM IMO.
• Trying to restart following this may get it to start right up like it's brand new, other times it will do this for 3 and even 4 starting cycles. Very dynamic.

So here's the troubleshooting/parts cannon order of operations;

• Throttle body cleaned with spray cleaner, very shiny
• Idle air control (IAC) valve cleaned with spray cleaner, while running, and while not running with IAC module removed from throttle body assembly
  • **It's clean enough I'd have no problem using it as a utensil, port passage is also clean as a whistle
• Audibly checked injectors with long-screwdriver-stethoscope technique. All are clicking and no obvious signs of solenoid failure
• Wiring for spark plugs were checked as well as the plugs themselves, engine runs perfectly fine when started so I don't suspect the coil rail is faulty
• Checked for vacuum leaks, visually and with an ether can (checking for idle RPM changes) all clear
• Ran a code scanner on it, checked running conditions of sensors, all appear normal
• Battery was replaced with an AGM (battery was going bad on it and died one day, what a bear to boost that was with this trouble starting issue)
• Followed TSB for injector 3 heat soak, MOPAR insulator wrap on injector 3 secured with ziptie, no change.
• Removed and checked the spark plugs, no cracks, electrodes were perfect, re-gapped them to the sticker-spec .035 (Some mention that .040 is fine as well, but I was able to rub off 18 years of undercoat from the sticker and see it calls for .035)
• Replaced the alternator, could see battery voltage dropping with blower motor on at idle, preventative at least as was still DENSO factory unit. Replaced with rebuilt CarQuest unit
• Replaced the pair of upstream O2 sensors, 2x NTK units, old sensors were worn but not faulty yet
• Changed fuel pump with a Delphi, new from RockAuto (I was praying hard this was the culprit, pressure was out of spec but not crazy low, calling this preventative for my sanity)
• Replaced exhaust header/air intake heat shield. Old heatshield was rotted and performing no insulating
• Throughout this time I slowly cleaned every ground I could see and resecured them

That's everything remotely related to this specific issue. The jeep has stalled while running, shifting from drive to reverse or vice versa. That has happened twice - maybe three times if memory serves - in the last year.

3 months ago it started to idle low/rough when stopped and in gear, and with the A/C off. I'm under the assumption this is unrelated but might not be. Will sometimes drop idle at a red light to well below 750, I think first notch on the post-refresh gauge cluster is 500, so it's dipping to that point but not enjoying running. I typically crank the AC for a moment and turn it off, or I'll quickly slot it into neutral and back into drive, it will stabilize at 650-700 after that until I get underway and stop again. My guess is it's the TPS on the way out as I've witnessed it hunt for idle a handful of times before putting A/C on to bring revs up. This is VERY intermittent and I can sometimes do an entire drive through the city (about an hour) without it happening.

This is a very long post to start off the thread, but wanted to make sure I got as much detail as I could as I've seen threads in the past that I thought may be the same issue as me but might be missing some key details for my case. The symptoms haven't really changed/worsened since they presented. Next step is taking apart the fuel rail and checking the injectors closely for leakage or faults. Has only thrown 1 potentially related DTC in April of this year, P0622: Generator Field/F Terminal Circuit. Added dielectric grease and resecured the connector, cleaned passenger side engine block ground, no code following that. Wondering if anyone else has had this issue, and if anything else they did differently than me seemed to have fixed it?

 

[Steel City 06]

Be sure to check all the lines coming from the gas tank. Not just the fuel line, but all the vent lines as well. If one or more are kinked or clogged, or if the charcoal vapor canister has given up the ghost, it can easily cause a stalling and hard starting issue.

 

[ChasUGC]

It sounds like the issue that I had with my Cat. many years ago. It would chug and stall on me, intermittently. I spent like $2500 dollars at the stealership and the problem persisted. Finally, I took it to a muffler shop and told them about the noise I heard and the problems. He tapped my cat. underneath with a rubber mallet, and it sounded like broken glass. So, my Cat. had collapsed inside, causing the exhaust to back up and stalling my engine. It was hard to start at times, because of the built up exhaust smoke, especially after it stalled. Replaced the Cat. and the problem went away completely. I was so angry with the dealership, and this problem was eventually a recall on my '97 Wrangler.

 

[broganobrien]

Updating this thread:

Starter died on me one morning, the hard starting issue probably set it back several years of useful life so can’t say I’m horribly surprised. This happened back in August, and I replaced it with a rebuilt unit from NAPA. Tonnes of torque rolling into the flywheel and the issue persists.

As of yesterday, the jeep has now thrown an ignition related trouble code (!!!):

P0320

Set Condition: No signal from the Crankshaft Position Sensor is present during engine cranking, and at least 3 Camshaft Position Sensor signals have occurred.

Now, considering my symptoms to date being heat-related and affecting fuel delivery, I’m betting on some kind of intermittent short in the hall effect sensor in the bell housing upon a hot startup. I have had this issue on a previous vehicle, but that one died after the tach went haywire - but it would refuse to start when warm and would start when cooled off. That one was easier to diagnose because it was just crank, crank, crank, UNTIL it was finally cooled off and would start right up. Easy money. The jeep is more intermittent and hasn’t caused a no-start condition to date.

After inspecting the wiring and confirming the paths are good, receiving ref. voltage, and have little resistance to the PCM and ground, I’ve ordered a MOPAR new CKPS.

Will update when that’s replaced, arrival estimated Tuesday and should be an easy swap with the automatic trans having it mounted on the passenger side of the bell housing.

Hopefully this finally puts this issue to bed.

 

[broganobrien]

Sensor install update:

New CKPS is in and the results are promising.

As I’ve said I’ve been battling this issue for several years, once I installed the MOPAR sensor it started right up and worked fine. Took it for a test drive and got it hot. Tested starting it immediately after turning the ignition off, and also after letting it sit a few minutes to let the heat soak.

So far so good, I’ll revisit here in about a week before I mark this thread as SOLVED. But for anyone else exhibiting similar issues, check those sensors and I guess just patiently wait for a code. This did not come up with a check engine light - it was dumb luck that I happened to check for codes when it was presenting.

The idle problem also seems to be addressed with this. W/o AC it held steady at just below 700RPM, stopped, and in gear and didn’t feel as strange as it used to.

 

[broganobrien]

Sensor install update:

New CKPS is in and the results are promising.

As I’ve said I’ve been battling this issue for several years, once I installed the MOPAR sensor it started right up and worked fine. Took it for a test drive and got it hot. Tested starting it immediately after turning the ignition off, and also after letting it sit a few minutes to let the heat soak.

So far so good, I’ll revisit here in about a week before I mark this thread as SOLVED. But for anyone else exhibiting similar issues, check those sensors and I guess just patiently wait for a code. This did not come up with a check engine light - it was dumb luck that I happened to check for codes when it was presenting.

The idle problem also seems to be addressed with this. W/o AC it held steady at just below 700RPM, stopped, and in gear and didn’t feel as strange as it used to.

Last update. CKPS has solved the hard starting issue consistently. Low idle problem still is happening when at operating temperature with AC off but will investigate that further.

 

[broganobrien]

Last update (for real this time)

The low idle appears to have been caused by a faulty/lazy/burnt up downstream O2 sensor. Against all available logic, it seems the downstream O2 sensor either; affected the target idle with A/C off on open loop, or somehow gave the engine poor feedback to achieve the target idle with the A/C off on open loop. I didn’t get access to a good OBD2 scanner until after the replacement, so didn’t verify what way it was happening. I can only guess it’s option #2.

Started with an P0161 B2S2 heater circuit malfunction code and check engine light. Hammered on it with a wrench, opted for a torch after that. Before getting the heat to it, it also displayed P0158 voltage high B2S2 (likely shorted from the hammering). After changing both the B1S2 and B2S2 units (California setup), the engine now maintains target idle at open loop and closed loop consistently. I was able to check the catalysts in both downpipes with a scope and appeared to be in tact. Snaking inside of B1S2 is a pain though.

I was under the impression that downstream/ post catalyst sensor had no effect on engine performance and simply monitored catalyst efficiency. So was surprised when this solved the issue.

I had also changed the camshaft position sensor without having a code showing. No obvious symptoms, but figured new crank sensor might want a friend? Wanted to change it for a while but that did not solve the problem, I would say it did make a difference in overall idle stability though.

Throttle position sensor also had a failure a few months ago and replaced that with no change in the low idle issue. Failure showed symptoms as surging at a stop at idle and awful throttle response, so figured that was unrelated. It was.

Friendly reminder to always change sensors with Mopar/OEM suppliers. I’ve strayed from that in the past and paid for it two fold. Do yourself a favor and spend a few extra bucks - if you can find them. Otherwise try salvage yards, or do as much research as you can before buying aftermarket stuff that runs on electrons.

After chasing the above gremlins for 3 years, can finally retire this thread and enjoy the jeep with the top off and the AC OFF AT A RED LIGHT!