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Fuel gauge question

whitneyj

whitneyj

NAXJA Forum User
Location
Mayville, WI
I've searched around and found a couple possible solutions to my problem, but I've still got a couple questions unanswered. I've got a 00 XJ that I've relocated the fuel tank. When I relocated it I had to splice in 30" of wire and turn the fuel pump 180*. Here's the problem. My fuel gauge doesn't work at all. I've check my connections and they all seem good. My oil pressure gauge is also reading a little wierd. Are they connected in some way? I can't seem to find a decent schematic.
 
On the later models like the '00, the gage signals come from the ECU/PCM. A common problem is the dash pod socket connection. Best is to pull the pod out and clean the connections, but people have had success beating on it (gently). The best schematics I have seem are in the FSM.
 
so turning the fuel sender 180* wouldn't have had any negative effects? or splicing in 30" of extra wire?
 
If the float arm can still go to the bottom when the tank is empty and to the top when full, 180 deg. shouldn't make a difference. But without seeing the shape of the new tank, I suspect you've got a problem there. Does the tank unit go in at an angle on the front of the tank like the stock tank?
 
The only downside to adding 30" of wire could be too much resistance in the splice(s). If done correctly it shouldn't cause any problems.
 
winterbeater said:
Yeah, the sender gives the signal to the PCM and then it's translated into a multiplexed signal to the gage. My point was that it is more complex than just the resistance directly changing the gage.
Click to expand...

I caught that from schematics. . . I'm going to ohm check the fuel sender here in a bit. I'll try and turn the fuel sender back around. I never saw a ground wire from the tank, only the harness. As far as the clearance goes, I moved my rear axle back 5" and needed the angled part of the tank to face the front of the vehicle to clear the axle's uptravel.
 
Alright, I know that it's been a while, but I've ohm checked the fuel gauge sender at the PCM, pin 26 and got a constant 200.5 ohms. I added a gallon of fuel and it didn't change. So correct me if I'm wrong, but that means I either have a bad ground, a spline that's causing alot resistance, or the float is stuck.

That brings another question. I hear people say that a butt connector shouldn't provide a voltage drop, or more resistance, if done properly. How do you use a butt connector improperly to provide a voltage drop?
 
Or, the resistance of the sender unit isn't changing for some reason. Probably even odds all around.

When you say "turned 180*", does that mean you turned it front-to-back or top-to-bottom? If you've turned it over without re-arranging the electrical connexions, your resistance signal will be reversed (which means you should read "Empty" when you're "Full" - and vice versa.)

I'm going to keep leaning toward an electrical fault caused by the installer here (sowwies!) since it's not behaving in a predictable manner according to most sensor faults I've seen...

EDIT - Try this - forget everything you've done to the circuit, and act like it's a vehicle you've only just bought and you're trying to figure out what's going on. Should give you a useful fresh perspective on the problem.
 
5-90 said:
Or, the resistance of the sender unit isn't changing for some reason. Probably even odds all around.

When you say "turned 180*", does that mean you turned it front-to-back or top-to-bottom? If you've turned it over without re-arranging the electrical connexions, your resistance signal will be reversed (which means you should read "Empty" when you're "Full" - and vice versa.)

I'm going to keep leaning toward an electrical fault caused by the installer here (sowwies!) since it's not behaving in a predictable manner according to most sensor faults I've seen...

EDIT - Try this - forget everything you've done to the circuit, and act like it's a vehicle you've only just bought and you're trying to figure out what's going on. Should give you a useful fresh perspective on the problem.
Click to expand...

I turned where the fuel lines come out 180*, not sure how that affected the float.
It probably was from the installer, he's been known to do these things ;).

That is a new angle. . . never thought that line before. I'll have to go back to the FSM and T/S it some more. Probably will start with removing the fuel sender to ensure the float isn't stuck and to properly T/S the gauge sender.

I appreciate your help, thank you.
 
whitneyj said:
I turned where the fuel lines come out 180*, not sure how that affected the float.
It probably was from the installer, he's been known to do these things ;).

That is a new angle. . . never thought that line before. I'll have to go back to the FSM and T/S it some more. Probably will start with removing the fuel sender to ensure the float isn't stuck and to properly T/S the gauge sender.

I appreciate your help, thank you.
Click to expand...

It's an angle that has worked well for me in the past. Drop the job, put everything away. Go have a coffee and a sammich.

Come back, and look at it like it's something that someone has brought in to you to fix. Forget that you've done the work to screw it up in the first place, and see what would have gone wrong to want fixing. It's a sort of "clear your mind" Zen approach that often gives you a much-needed shift of view.
 
Once again thank you to 5-90 for the insight. I finally got a free weekend and pulled the cover to access my fuel tank and BAM! Hit me right in the face. The fuel module has to be clocked in a specific way-hence the arrow cast into it to tell you which way it needs to be. Mine was not correct. . . and I call myself a mechanic. . . :)
 
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