Fuel guage reads full always

[Bones]

OK so I have had this problem since I did the Xploder swap in my 86 BII 2 years ago, lol. I figured out mileage and always error on the "put more fuel in" side, hahe. But it sure would be nice to know how much fuel is in there, as mileage means squat when in low range. I have the xploder dash and in-tank sender/pump and even when I unplug the sender wires from the tank the gauge reads full when the key in turned on. I figured it was a ground problem at the tank or somewhere in between but now I'm not sure what the problem is, I took out the in-dash gauge cluster to see if the plug wasn't attached properly, or maybe I missed a ground wire under the dash when I swapped the dash and wiring harness in, but I haven't found anything loose or not connected.

Anyone have any idea of what I may have missed??


Thanks in advance for any help or ideas rendered.

[Bones]

OK, So here's few details about my rig I hope will help narrow down the trouble shooting for you guys.

So it has a brand new (as of 2 weekends ago) fuel tank, the sender I was using originally was the BII stock one. I figured it was a ground problem at first and after adding a separate ground wire to the ground circuit (orange sender wire) I found that nothing had changed, so I then figured that the BII sender was not compatible with the Explorer fuel gauge and that's why my gauge went to full when the key was on and/or engine running. So when I swapped in the new tank I also swapped in the Explorer sender ( which worked fine in the explorer before dis-assembly), all cleaned and die-electric greased up the connector. The wiring connector needed to be changed because the BII has a plug at the tank and the Explorer has a plug about 2 feet from the tank and the wires are permanent in the sender. All the wires and connections are clean and contacting correctly at the tank end as well as at the gauge end as far as I can tell. I pulled out the gauge cluster to try and find what I may have missed there and couldn't see anything that was unhooked or loose or a ground wire I may have missed hooking up, and found nothing out of place or that stood out. I also opened up the wiring loom along the frame to see if there was a bad wire or something and found none. Everything worked fine before when it was in the explorer and now the fuel gauge is bunk for some reason.

What the heck am I missing here?

[PHROX]

Well, my guess would be that a woire is grounded that shouldn't be. The sending unit has a resister that changes the resistance the more gas you put in the tank. Some change it from high to low, others change from low to high. Ford changed them a lot. The ranges also changed. But incompatability doesn't sound like your problem. It sounds like a wire is grounded so that when you apply the charge it shorts back to the guage making it think the resistor is reading no resistance hence full. If that's not it you can check the guage by grounding and ungrounding the wires. It should bounce full or empty. If it sticks on full it might be a bad guage. Hope all this helps you out. I put a 93 t-bird dash in my 87 bronco 2 and the guage read backwards, empty when full, full when empty. Turns out I had a compatability issue. Took a lot of looking on the net to figure out what's compatible with what.

[Bones]

Right on!!! Thanks for the responce PHROX, much appreciated. So with "your" gauge compatibility issues would reversing the wires have worked?? ie. pos. to neg. and neg. to pos.??? Just currious.


Thanks again.

[PHROX]

way late response, but the answer is no. the ohm ranges were different as well. cant remember the numbers but it doesn't matter.

[drofman]

Does it have a IVR? Connect a test light between gage lead (BK/LG) at instrument custer and ground. The light should blink regularly with the ignition on. Normal gage resistance in a 1988 is 10 to 14 ohms. Check gage calibration with 10 ohm (high) and 73 ohm (low) resistors. If gage tests within calibration, replace sender. if gage tests out of calibration it might be IVR. I think PHROX may be right. May have a pinched wire to gound.

[drofman]

sorry i must of had a few when i posted last. the BK/LG is the power feed for the gage. the Y/W is the wire that goes to the sender/fuel tank selector