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Old March 11th, 2018, 10:01
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Ben824 Ben824 is offline
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Intermittent gauges mystery

Hey guys, been a while since I was on here. So my uncle brings his 99 XJ Sport 4x4 Auto 4.0 to me for work that needs to be done to it.

Recently he brought it to me with an intermittent gauges situation. I think its the usually dirty contacts so I pull the gauges and clean the contacts, put a little dielectric grease on there and put it all back together.

That did not fix the problem, not even the slightest.

First, the XJ will not pass emissions here in Georgia because it is still in Readiness.

Second observation, all the indicator lights and the odometer still work regardless of the gauges being operational.

I thought maybe the grounds for the computer harness might be dirty or corroded so I went to address the grounds on the inner fender right next to the computer and still no change in the problem.

I checked the battery negative post, the negative cables, and the negative ground connection to the chassis. I even relocated the negative chassis ground because the old one was corroded with rust and the bolt snapped off when I tried to remove it. Still no change.

I even ran a test lead from the negative post all the way over to the negative computer grounds and no change.

What am I missing here?

What can I try next?

Is this maybe a faulty ECM?

I have a spare ECM from my 97 XJ I could test with but I know they changed something in 98 or 99 and started storing the VIN in the computer, will that be something of a problem is I try and hook the 97 computer up to the Jeep for diagnostic testing and ruling out of the faulty computer idea?
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Old March 11th, 2018, 17:33
Dragonslayer Dragonslayer is online now
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Re: Intermittent gauges mystery

Check the ground wires that are bolted to the passenger side of the engine block at the
threaded stud holding the oil dip stick tube bracket.

When I say "check" I mean you need to physically remove the nut, check for frayed wires, and clean or repair them.

A few years back, my own gauges were going wonky and I did a "visual" check and
tightened the dipstick tube bracket nut, only. It didn't do anything.

After more frustration, I went back to it and removed the nut - and the ground
wires had been holding on the the ring terminals by only a few strands and they
fell apart when I tugged them off of the threaded stud!

I soldered on a 4-inch length of extension wire ("pigtail"), and new ring terminals,
and all has been good since.

Lesson learned.
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Old March 12th, 2018, 05:31
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Ben824 Ben824 is offline
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Re: Intermittent gauges mystery

Quote:
Originally Posted by Dragonslayer View Post
Check the ground wires that are bolted to the passenger side of the engine block at the
threaded stud holding the oil dip stick tube bracket.

When I say "check" I mean you need to physically remove the nut, check for frayed wires, and clean or repair them.

A few years back, my own gauges were going wonky and I did a "visual" check and
tightened the dipstick tube bracket nut, only. It didn't do anything.

After more frustration, I went back to it and removed the nut - and the ground
wires had been holding on the the ring terminals by only a few strands and they
fell apart when I tugged them off of the threaded stud!

I soldered on a 4-inch length of extension wire ("pigtail"), and new ring terminals,
and all has been good since.

Lesson learned.
Haven't tried those grounds! I wouldn't have thought that the grounds for the block would cause an issue like this but I guess anything is possible! I will get him to bring it back to me and give it a try!
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Old March 12th, 2018, 17:20
Dragonslayer Dragonslayer is online now
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Posts: 281
Re: Intermittent gauges mystery

Oh, you'd be amazed at how important that ground is. It's called "G101" on the FSM
schematic and all sorts of things in the car depend on it being clean and proper (including the PCM, fuel injectors, O2 sensors, instruments, etc.). The wires there
are short and taut and after a few years of engine vibration and acceleration torque,
and bumping into the wires during oil filter changes, the wires become fatigued and
they loosen and fray. Replacing the ring terminals and adding an extension
"pigtail" fixes this.

...but wait ... there's more (maybe) ...

It later occurred to me that there is another instrument ground on '97+ XJs.

It is ground "G107" on the schematic. Look for black wire(s) on a ring terminal that is
screwed to that sheet metal - located in the area near the glove box lamp switch.
You'll need to remove the glove box to access it.

Try fixing ground G101 first. If that doesn't cut it ... then inspect the ground at G107.
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