Strange, intermittent gauge cluster issue...

[JeepNoob]

'96 XJ 4.0 Sport, 5-speed, 4x4, no ABS, no cruise, no fog lights, pretty much as basic as you can get...

I was driving around yesterday when my tachometer, speedometer, and fuel level gauging starting acting funny. Sometimes the tach and the speedo would bounce around erratically (especially when accelerating), sometimes the tach and the speedo wouldn't register anything at all (but when this happened, the fuel level gauge would go WAY up, think like 1/4 tank or more past the full mark and the low level light would come on.) All other gauges act fine. The gauges behave much better when driving on the highway at a steady speed.

I've tried checking Mitchell's wiring diagrams to see if these components are all connected somehow (common 5V reference wire or ground) but couldn't really find anything...) I think the gas gauge going to full or past when the other two gauges don't work is a pretty damning piece of evidence and leads me to believe that a 5V reference signal or a ground for the fuel pump is intermittently bad, which is somehow affecting the other two. Fuel pump was replaced with a complete Crown (I know, I know... I suspected my fuel pressure regulator may have been bad and it's integrated into the module. :smsoap fuel pump module maybe 3 or 4 months ago. I've also had my speedo act this way, but the tach acted fine. Replacing the speed sensor solved the issue (probably did that 6 to 9 months ago.)

I'll do some more digging, but does anybody know off the top of their head how the variable resistor in the fuel pump module works? Does the resistance increase or decrease as the fuel level increase?

 

[Vernicious]

The gauge cluster should be electronic completely. They are known to back out of the sockets. You can pull the cluster, clean the contacts and put it back in with some force. Before looking for a shirt that may not be there, you need to look at the cluster.

 

[JeepNoob]

Update- pulled the dash apart and checked the connectors. Everything looked good, no corrosion or other issues as far as I could tell. Gauge cluster looked like it had the original, OEM part sticker on it, so I'm guessing it's 20+ years old. Sprayed the contacts with some electrical cleaner anyways. Connectors seemed to fit snugly, but the issue is still there. One thing I did notice while cruising down the highway is that the speedo needle will stay pretty stable right up until I hit an expansion joint or something. At this point, I'm thinking that the electromagnets inside the gauge cluster that move the needles themselves are weak and the whole gauge cluster needs replaced...

 

[90xj06]

if i had to guess it sounds like its losing a ground. i haven't taken a cluster apart so it could be a connection inside. could be a cracked solder joint.

 

[dan1977p]

If you think the fuel pump ground is bad, you should check in side the drivers rear quarter panel. That's where that ground is and is known to loosen up or corrode. There's even something on Cruiser54's site for adding an additional ground for renix era jeeps. Worth a look.

 

[JeepNoob]

Found and solved the problem today after buying a new gauge cluster which didn't fix the problem. Hopefully, the junkyard will refund me.

After checking a few other forums, it seems that the speedo, tach, and fuel gauge all share a common ground. Unfortunately, the Mitchell wiring diagrams I was looking at just have the magic black box that represents the instrument cluster and a couple of wires and terminals that are just labeled "GND." The common ground in question is a black and orange wire that's grounded at the passenger-side of the block, behind the distributor and near the oil tube. (In fact, it looks like the bolt that holds them down also serves as a dipstick tube bracket bolt.) After checking mine, sure enough, the orange and black wire had broke off the terminal. The ground bolt seemed pretty loose too. Spliced on a new ring terminal, cleaned the other two terminals and everything works great.

Learned a few things while I was at the junkyard though. For one, there's a couple different styles of gauges, one that I suspect was used in the early days and has the fuel gauge next to the speedo and a couple of idiot lights, the one like mine which has the tach next to the speedo, and 4 actual gauges, and the '97 and later with the digital speedo. If you have a gauge like mine, you can just pull another one out of the junkyard. The options, year, etc. won't matter, and the functionality will be exactly the same, since if you didn't have a particular option, the connectors won't have the pins for that option or idiot light (I.E. ABS, the upshift light for a manual transmission, etc.)

Try to look for a gauge cluster that's actually been sitting in a vehicle. Granted, it's pretty dry where I live, but the only gauge cluster I found that had pin corrosion was one that had been sitting out in the elements on the floorboard. Don't sweat dirt and dust too much either. Mine had a bunch of dust on the outside that cleaned right off with some compressed air. If you want to clean the inside or the lens, on mine, there were 4 plastic screws that held the lens on. Remove those, pull up on the trip meter knob to remove it, and you can remove the lens and plastic trim piece between the actual gauge faces. The idiot light panel on the left is held on with two plastic screws. Also, don't think the gauge cluster is broken from the junkyard if the smaller gauges are reading something other than zero or the trip meter doesn't reset when you try to reset it. The gauges will read correctly and the trip meter will work once the gauge is connected and has power going to it.