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Skipping and misfires


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"Tanner, I'd check your temperature switch (cost me $20 from Carquest/Advance).  The white epoxy that acts as a thermistor gets old and cracks with age.  It's a PITA to get to but that would explain the temperature related aspects of the issue.  While you're back there (I removed my fuel rail to get to the switch), CLEAN THAT GROUND!  11/16" Wrench, PB'laster, and a wire brush."

 


 

I will have to look into that because I'm not sure that my temp sensor back there is any good. It's the only sensor on the motor I didn't replace went I rebuilt because it almost looked as if it was cross threaded in there and I didn't want to risk it at the time. But hearing that it has helped this issue you have been having I will have to venture in that direction.

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Yep, looks cross threaded because of the angle and when I installed the new one, I did get a few brass shavings.... Probably should have cleaned the hole with a tap but it's in and no leaking.

 

Seriously though, clean that ground with the sensor out. Much easier than having to dig back there again.

 

Also to get the connector off the sensor I found it easiest to squeeze the narrow ends of the connector. I don't know if mine was missing a release lever but be careful not to crack the connector if you use pliers.

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Tanner, I'd check your temperature switch (cost me $20 from Carquest/Advance).  The white epoxy that acts as a thermistor gets old and cracks with age.  It's a PITA to get to but that would explain the temperature related aspects of the issue.  While you're back there (I removed my fuel rail to get to the switch), CLEAN THAT GROUND!  11/16" Wrench, PB'laster, and a wire brush.

 

If you're referring to the sensor/switch on the left rear of the cylinder head, that's for the dash coolant temp gauge. It's a sensor if you have a gauge; a switch if you have idiot lights.

 

On your 92 HO engine temperature is monitored by the ECU based on input from the coolant temp sensor on the thermostat housing, not by the sensor on the cylinder head.

 

Tanner has a 90 Renix - entirely different from your 92. The Renix uses output from the temp sensor on the radiator.

 

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Whoops didn't realize he had a Renix.  I thought I had read that about the temp switch being for the gauge only, and that was why I hadn't replaced it earlier....my gauge was working (at least the needle moves when I let the truck warm up....as for accuracy, I don't know for sure but it didn't match my IR gun).  I do know my problem has been gone for 2 days which is the longest the Jeep has run without issues since October or Nov when this started.  Does anyone have a electrical diagram of the sensors on the 4.0 H.O. motor?  I'm curious now if that temperature switch could have shorted and effected my ECU by drawing down the voltage, although that doesn't explain why my gauge was still functional.

 

 

Really, I'm just waiting for the problem to come back again at this point because the fix I applied isn't logical.  I think.

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Well, skipping and such is solved, A/F gauge is in (running almost lean....idles at 15, runs right at 14.6-14.7 at cruise or WOT).  My coolant temp gauge now no longer functions (It did appear to work with the previous broken sensor, but also had the skipping issue).  My question now is does anyone know the resistance range of the temperature switch (the little guy that controls the dash gauge)?  I'd like to bench test the new unit and the wiring to find my issue.

 

I hear these 4.0s can tend to run hot, esp in the deep South and I'd rather not blow a head gasket.

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Well, skipping and such is solved, A/F gauge is in (running almost lean....idles at 15, runs right at 14.6-14.7 at cruise or WOT).  My coolant temp gauge now no longer functions (It did appear to work with the previous broken sensor, but also had the skipping issue).  My question now is does anyone know the resistance range of the temperature switch (the little guy that controls the dash gauge)?  I'd like to bench test the new unit and the wiring to find my issue.

 

I hear these 4.0s can tend to run hot, esp in the deep South and I'd rather not blow a head gasket.

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Found the issue. Sending unit I got wasn't for a gauge, it's for the idiot light.

 

Edit: no, I just thought I did.

 

The major retail parts houses don't carry this piece. If you ask for with the gauge you get a sending unit with a threaded stud coming out of the top. The proper piece is Mopar 56027012 Temperature Gauge Switch.

 

Should look like what the parts house have for the dummy light but with a white or cream colored plastic connector.

 

 

113b39f23a60f1fd2d8ab8cb1fa52cdc.jpg

 

Sent from atop the porcelain throne.

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Lol, "doesn't fit your vehicle". Now I know why I couldn't find it..... God I hate those filters sometimes.

 

Thanks!

 

I guess '92 is the year it changes then, making it a one-off. I'll have to remember that if I run into similar sensor issues.

 

Sent from atop the porcelain throne.

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  • 2 months later...

14mm on mine.

This thread. Never fully resolved this issue.

 

 

It seems like I cleaned the grounds and it helped until there was a weather swing and then the issue returned. Cleaned them all again, weather changed, issue comes back.

 

Anytime the temperature went from hot to cold, the problem came back. It looks like a ground issue but I can't get it to stay gone.

 

And yes, I did cruisers tips and then some.

 

Sent from atop the porcelain throne.

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  • 2 weeks later...

One thing I haven't seen mentioned is the egr. It could be sticking open or leaking. When you first drove it without the exhaust hooked up there was little or no back pressure. Now that is hooked up exhaust gas may be flooding the intake.

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One thing I haven't seen mentioned is the egr. It could be sticking open or leaking. When you first drove it without the exhaust hooked up there was little or no back pressure. Now that is hooked up exhaust gas may be flooding the intake.

I will have to try that. Was just up in Atlanta this weekend but didn't get to work on the MJ. Spent most of my time on my house instead.

 

Sent from atop the porcelain throne.

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One thing I haven't seen mentioned is the egr. It could be sticking open or leaking. When you first drove it without the exhaust hooked up there was little or no back pressure. Now that is hooked up exhaust gas may be flooding the intake.WW

When I rebuilt my motor I deleted my egr but I have the same problem tex has. 

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Took it out for a spin yesterday. Thrashed it up and down neighborhood roads, county connectors, and state highways. Not one hiccup.

 

I think that's what is most frustrating about this problem....when I do have time to work on it, the issue disappears.

 

Sent from atop the porcelain throne.

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  • 2 months later...

Well, I burned up an alternator. Picture attached. 33521b1a8b558e4ee684acb5794ec332.jpg

 

I've had the issue still come and go, although tonight I had a possible breakthrough. Replaced the alt with the 130A dodge truck one and ground down my bracket to make it fit. Old one is clearly shot. Read somewhere that a bad negative connection on the battery can cause alt failure, so cleaned and retightened my negative post (didn't really tighten, the cable end is shot). Issue came back with a vengeance. Fought it all day today and half of yesterday. Tonight, moved my negative cable on battery post and problem was instantly better (not solved but better it seemed on the test drive). Going to keep trying this as a "fix" until I can replace the cable with a heavier gauge one.

 

Side note: as my alternator was dying, I kept getting a tps engine code (24 I believe. Tps voltage out of range). I've replaced this thing 3 times this year with napa or Mopar parts after reading 4.89vDC @ idle. Think this is relevant?

 

Sent from my SM-G930T using Tapatalk

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If you haven't already, switch out your cables for bigger gage cables or just change them out because they are old...

I went from a 60amp to 100amp on my truck and melted the wires, luckily I caught it in time and not burn down my truck...

 

Pics of wires....

 

Damn, even without any extra load (lights, winch, stereo, etc)?

 

I was trying to get a set of pre-made wires but it's looking like I'll be buying a hydraulic crimper and making my own. Anyone have gauges/ lengths needed by chance?

 

Sent from my SM-G930T using Tapatalk

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Side note: as my alternator was dying, I kept getting a tps engine code (24 I believe. Tps voltage out of range). I've replaced this thing 3 times this year with napa or Mopar parts after reading 4.89vDC @ idle. Think this is relevant?

Most all of the HO sensors use a 5VDC reference voltage. This voltage is generated by the ECU and the tolerance is tight. One thing you should try is disconnect the 60-pin connector from the ecu and check for recessed pins, then clean both sides up carefully with a good electrical contact cleaner. Do not use dielectric grease when reconnecting. This usually brings the sensor 5V reference voltage back up to specs by cleaning up any corrosion (resistance) from the pins. 

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