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Fuel pump and gauge problems?


New member
Hi guys, I have an 88 XJ with the 4.0 engine and I'm having problems with the pump and possibly gauge.

I was driving along and it stalled on me, I restarted it and it died right away and I tried again and it died right away.

I figured burned out fuel pump cause I was spending most of the day on empty.

So I unpluged the sending unit connection and connected the multimeter to the power and ground wires and if put the key to the run position it would read 11 volts for a couple seconds. Just like when you go to the run position and the pump primes for a couple seconds so I figured it was the connection or pump.

I pulled out the sending unit to change the pump and tested it and found that the pump works, I tested it through the sending unit connection so I figured that was ok too. Then I tested each individual connection and they all work so I called it good and put it back in the tank.

One question here, when I tested the connections the ground seems to be connected to the other connections but that seems right to me cause it would go through the gauge sender and fuel pump it self right?

So me and my buddy are thinking its a ground problem of some sort? But I followed the connection and its got a connection to ground as far as I can tell.

Now on to the fuel gauge, with everything connected and the keys in the run position the gauge goes way past full pretty much pointing out the passanger side of the jeep, kinda like my oil pressure gauge with a bad connection. It stays the same with the connection between the jeep harness and the sending unit unplugged.

Is this another sign of a bad ground or is the connection between the harness and the sending unit not getting through?

Thanks for the help.
I am having similar probs. If my guage get to about 1/4 tank reading on my gauge, whenever I take corners it eithers dies, or almost dies (while in the corner) once out of corner it is fine. Any ideas on the culprit. Need help was thinking the fuel pump, already changed fuel filter. Anyhow, if it is fuel pump what pump should I get (aftermarket). I have a 95 XJ 4.0.

If you get another fuel pump DO NOT getone from auto zone get one from o'rileys or someother place because the auto zone pumps have a large tendency to just quit working we replaced one were i work 2 times it would run for about a week or 2 the just quit. then we call o'rileys and got another and it hasnt had any problems for the last 6 months dont get me wrong i love auto zone but some stuff just isnt that good (the pumps sold at auto zone are AC DELCO brand just F.Y.I.) but this is true for most other places as well.
Before getting a new pump, make sure the fuel pump ballast resistor isn't open. Just short around it. The symptom is that it will crank and fire up. As soon as you quit cranking it dies in a second or two.
old_man said:
Before getting a new pump, make sure the fuel pump ballast resistor isn't open. Just short around it. The symptom is that it will crank and fire up. As soon as you quit cranking it dies in a second or two.

I do have a spare (as far as I know I havn't tested it yet but it looks brand new, the bag is open though) but would I get power to the sending unit connection if that resistor was gone? Cause I get power back there as I said in the original post? Car wiring does baffle me though.

I also just tested a couple other things just now.

I check ground from the sending unit to the frame and I have continuity and I plugged the sending unit in and backprobed and they all have continuity.

The whole thing is driving me crazy.
Ok I swapped that ballast resistor and it works now. I havn't started it yet because I'm putting on a new alternator also but it primes so I'm going to figure its going to run ok now.

So why did I have power back there? and why wasn't that power enough to run the pump.

Of course I still have a gauge that is way off, any ideas on that one? I might use the odometer method of telling when to gas up for the rest of the winter but I really want a fully working, accurate gas gauge cause it was before I did this.
old_man said:
The pump power and the guage power are different.

??? What question are you answering there?

That my gauge is off? They both went south at the same time so they seem related. Maybe it just got tweaked when I put it back in or took it out or something.

So I read in the manual what the ballast is for but why wouldn't it prime in the run position with a bad one? It says in the book that the resistor is only used once it is running?
Any other thoughts on the fuel gauge? Does having it point out the passanger side mean its not getting signal from the sending unit?
One question on the fuel gauge, does it stay in the same position no matter what the level of the fuel is? The simple test is to swap another from the junkyard if available. You can take the sending unit out of the tank and hook your meter to it and check to see that the potentiometer is working right. I think that some years had the self testing gauges that go to full travel and back down whenever you turn the key on but I don't believe the '88s were that way.
Well I'm not climbing under there again till the ground is warm and dry, but I will try those things. To me it just seems like a non connection or something. I can't tell if its going to move yet till I put some miles on it.

I just figured someone would know what happens to the gauge if you have no connection.

Oh yeah it doesn't make a difference if the sending unit is plugged in or not the gauge shows the same thing.
BTT, anyone have any more ideas about the gauge thing? Is it doing what it would if I wasn't getting a signal from the sending unit?
Figured out my problem, I havn't had a chance to fix it yet cause its cold and snowy out there. I'll borrow my dads garage in the near future to fix it.

I went out and tested my sending unit presently in the truck and its showing no connection between the ground and the gauge sender so I guess the wire is disconnected in the tank or something. With it totally unplugged it does the same as now, points to the passanger side just like my oil pressure gauge does when its not getting a good connection.

I have a spare sending unit but its out of the smaller tank, I plugged it in and it works correctly so that was my confirmation that its just the sender and not the gauge or any harness wiring or plug.

Figured I would post this for anyone else in the future having this problem.