Gremlins

[GranpaQB]

A few gremlins have been popping up and I can’t seem to fix all of them. My gas gauge keeps going from empty to full and back again, the speedometer doesn’t work and it wouldn’t start. First time I got it to start was by changing out the camshaft sensor (hadn’t used OEM when I changed it last year and learned hard way). Vehicle was driven for about a mile then wouldn’t start again. I got it to start by changing the location of the battery ground and putting on a new terminal (was having a machine gun sound so therefor not enough power to starter).

My speedometer issue has done this before and I had fixed it by taking out the sensor on the rear axle and sanding around the axle to get rid of the rust and therefor have a better ground. Tried it again but that didn’t work.

And as for the gas gauge I pulled out the gas pump and changed it but that didn’t solve the issue at all. I have access to a ton of Liberty’s at the local junkyard so it wasn’t a big deal.

Any ideas since both are issues with wires coming from the rear so are they related?

 

[GitEmSteveDave]

I had a similar problem on my Sunbird. It turned out it was a ****** battery terminal shorting against a body component and/or being loose.

 

[Billwill]

A few gremlins have been popping up and I can’t seem to fix all of them. My gas gauge keeps going from empty to full and back again, the speedometer doesn’t work and it wouldn’t start. First time I got it to start was by changing out the camshaft sensor (hadn’t used OEM when I changed it last year and learned hard way). Vehicle was driven for about a mile then wouldn’t start again. I got it to start by changing the location of the battery ground and putting on a new terminal (was having a machine gun sound so therefor not enough power to starter).

My speedometer issue has done this before and I had fixed it by taking out the sensor on the rear axle and sanding around the axle to get rid of the rust and therefor have a better ground. Tried it again but that didn’t work.

And as for the gas gauge I pulled out the gas pump and changed it but that didn’t solve the issue at all. I have access to a ton of Liberty’s at the local junkyard so it wasn’t a big deal.

Any ideas since both are issues with wires coming from the rear so are they related?

What year/model is your Jeep?......if it is a wiring issue I can help you if I know the year/model we are dealing with.

There have been lots of posts where the pigtail going to the rear diff sensor rubs against the e-brake cable or rubs against chassis nearby.
Also often a bad connector pin where good contact is not made to the sensor itself. I had this problem on my 2002 Export CRD where the speedo stopped working. I cleaned up this connection....speedo worked again but CEL light stayed on for about a week before going out which is normal as a few good runs are needed to clear the CEL.

The 2005 KJ all models have a TSB issued whereby 2005 models rear diffs were filled at factory with wrong oil. This oil chewed up the speed sensor and owners needed to take their vehicles to the Dealer to have the diff oil drained, diff cleaned out, new sensor fitted and correct lubricant used.

Probably worth replacing this sensor in any case.

The fluctuating fuel level sensor could be a wiring problem but first remove the fuel level sensor from the fuel tank and check that it is clean and moves smoothly and all electrical connections in that area are good.

Early KJs do not need the tank to be dropped....lift up the carpeting in the cargo area...drill out the pop rivets holding the base down to get to a removable panel. Later KJs you need to drop the tank!

 

[GranpaQB]

It’s a 2002. I changed out the whole fuel pump assembly by going through the floor but it didn’t change anything. I have also rewired the pigtail and insulated the crap out of it so that it is impossible to rub through. I had cleaned up the wiring that was grounding the battery and the ecm but I am not sure it is perfect and will redo. I am from up north a rust gets everywhere so it can be anything. The gas gauge keeps jumping from empty to full back to empty every minute or so while driving no matter how much gas is in. Does this ring a bell with anyone?

 

[Billwill]

If you do not have the wiring diagrams download the 2002 KJ Service Manual here...includes the wiring diagrams in section 8W.

Page 8W-30-4 shows the fuel pump module which has a variable resistor which drives the fuel gauge.

The Black/Light Blue wire on pin 2 of the connector on the fuel pump module is supplied Ground from the PCM C1 pin 4 via connector C105. If you measure this Black/Green wire at the pump module you should get 12 volts with respect to battery positive.

The Dark Blue/White lead at the pump module should show a varying voltage to ground depending on fuel level....between about 8 volts and 2 volts I think.
This lead goes through several connectors....C100, C201 C307 and C3 pin 26 on the PCM.

The Wiring diagrams give the locations of all these connectors so it is worth re-plugging them.

What is more likely is that one of these leads has a break in it or is chaffing through to chassis somewhere which is why the gauge moves up and down.

You would need to fit a voltmeter to these wires at the pump module with long leads so you can watch the meter while driving......the Black/Light Blue wire should be steady with reference to battery positive while the Dark Blue/White wire should show a steady voltage with reference to ground while driving.

Service Manuals:Index of /manuals/Jeep/KJ

I am struggling to download these wiring pages on this forum at the moment! The speedo problem could also be a wiring problem.

 

[GranpaQB]

If you do not have the wiring diagrams download the 2002 KJ Service Manual here...includes the wiring diagrams in section 8W.

Page 8W-30-4 shows the fuel pump module which has a variable resistor which drives the fuel gauge.

The Black/Light Blue wire on pin 2 of the connector on the fuel pump module is supplied Ground from the PCM C1 pin 4 via connector C105. If you measure this Black/Green wire at the pump module you should get 12 volts with respect to battery positive.

The Dark Blue/White lead at the pump module should show a varying voltage to ground depending on fuel level....between about 8 volts and 2 volts I think.
This lead goes through several connectors....C100, C201 C307 and C3 pin 26 on the PCM.

The Wiring diagrams give the locations of all these connectors so it is worth re-plugging them.

What is more likely is that one of these leads has a break in it or is chaffing through to chassis somewhere which is why the gauge moves up and down.

You would need to fit a voltmeter to these wires at the pump module with long leads so you can watch the meter while driving......the Black/Light Blue wire should be steady with reference to battery positive while the Dark Blue/White wire should show a steady voltage with reference to ground while driving.

Service Manuals:Index of /manuals/Jeep/KJ

I am struggling to download these wiring pages on this forum at the moment! The speedo problem could also be a wiring problem.

Thanks Billwill now have a project for the weekend.