PNWjeeper

Hello everone I'm new here and I have some questions about two of my gauges my oil pressure and fuel gauge. The oil gauge jumps between about 2 psi in drive at a complete stop and when i take off it jumps to about 120 psi when i finally get to a good cruising speed it levels off at 40 psi and in neutral it stays around 20 to 30 psi. as for the gas gauge at least 90% of the time the needle is pinned to where the screw is that holds the plate on, that is untill my gas light is about to turn on then it moves between the E and the screw depending on if im going up a hill or taking off from a stop. I think i may have screwed it up when trying to hot wire my tail lights to come on when the car was on (later finding out it was just because of a blown fuse) and when i hooked it back up is when my gauge started this. Any ideas would be great especialy if i dont have to buy any thing seeing as im broke untill taxes come in. oh and its a 90' XJ 4.0 auto. thank you in advance.

cruiser54

You can try this. Can't hurt and might help.

Improving the Instrument Panel Ground
The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without wearing a hat, you will see a black wire attached to a shiny piece of metal almost directly above the hood release ****. The screw will have either a ¼" or 5/16" head on it.
This ground point is responsible for handling the ground circuit for the following items: Dome lamps, Seatbelt and key warning, trans comfort switch, wiper switch, headlamp switch and delay module, fog lamp switch, cargo lamp switch, all instrument panel grounds and illumination, power windows and door locks, cruise control dump valve, and a few more things.
The problem is that where the ground point is located does not have a good contact with the chassis where the ground should be. The solution is simple.
Make up a jumper wire with #10 gauge wire about 10" long. On one end, crimp on a ¼" round wire terminal. On the other end, crimp on a 3/8" round wire terminal.
Remove the screw from the existing ground wire and attach the small terminal of your jumper so that the original wire and your new jumper share the same attaching point, one over the other.
Look above the driver’s side plastic kick panel just forward of the top of the hood release ****. You will see an 8mm stud there. Attach the large terminal end there with a washer and nut over it tightened securely.
**Special note for Comanche owners: Make your jumper wire 12" long and attach it on the driver’s side kick panel close to the fusebox on the 8mm stud.**
　
Revised 11-29-2011

PNWjeeper

Wow that was fast, thanks I'll give that a try when i have a little more spare time and let you know if it works

cruiser54

Feedback is mandatory and expected.

PNWjeeper

Would 16 gauge wire be fine because i have that or should I find some 10 gauge

cruiser54

Probably will be just fine. If in doubt, run 2 of them.

PNWjeeper

Alright so I ran the two wires and the pressure gauge is better it now reads about 30 to 60 and will occasionally jump up to what would be 120 but there is no change with the fuel

cruiser54

That's called progress.

Check out the plug at the fuel pump module at the tank. Unplug it, visually check it, spray both sides out with electronics cleaner and plug it back together.

PNWjeeper

I couldn't get it to unplug from the fuel tank but I did unplug and clean the connector about a foot and a half from the tank but that didn't change anything. I forgot to mention when I hot wired the tail lights I think I did it to the fuel gauge wire if I remember right it was a purple wire

PNWjeeper

So I'm gonna give this another shot, just an update (for those who read the full post) my pressure gauge is still working fine 90% of the time. But my gas gauge is still all f'ed up. So how and where do I test the resistance for the fuel gauge( which from what I've read is how the gauge works) and what should I be looking for as far as numbers go for the resistance at say 1/4 1/2 and full tank. Thank you.

Radi

Old style: 90 ohms full and zero ohms empty

New style: 5 ohms full and 105 ohms empty

There was a change made in the early 90's to the sender operation, I think 91 was the last year for the "old" style.
measure @ the connector at the tank.

cruiser54

90 should be the old style.

PNWjeeper

So there were three wires a black (ground) a purple and an orange. So on the ohms test the orange wire tested at 93 ohms, there was also a purple wire which I tried to test and got no response. And my tank is almost empty

cruiser54

!!RC orange is fuel pump power and purple is sending unit.

PNWjeeper

Just to make sure the car doesn't have to be running correct, just in the on position? And if so does that mean my sending unit is shot if I get no response from it?