Fuel Gauge Troubleshooting

[kastein]

Sorry about that, cleared a few out. I should really go through my inbox one of these days (or just delete everything, most of it is over 10 years old at this point) but I cleared enough room for now.

Thanks for the video! It looks like it's still set private though, you need to set it public in your video list for people to see it. You can also set it a certain way so only people with the link can see it but I can't remember what that setting is called.

 

[fenns7]

2nd try at making vid 'Public' so hopefully now sorted.


Quick Q: Which is 'Track 1' - uppermost or lower?
*this photo may be of use to someone researching this:

 

[Saudade]

I have no idea. Measure them both. We know what Track 1 should read. The other then becomes obvious.

 

[kastein]

I seem to recall the larger radius one is the ECU curve on 96 but it has been a while since I measured so who knows if that's correct. Guess I've got a 50-50 chance... :looney:

The easy way to verify is to measure end to end on the resistor strip fingers, you'll get 105ish on the gauge one and 1100ish on the ECU one. At that point you know. Though it is unlikely it really matters to get a detailed curve data set because, well, it's one year only info, the ECU only cares for a few reasons that likely don't require much precision, and given the odd shape of the bottom and top of the tank, the angle the sender is installed at, and the linear level to rotary sender movement translation, it will be way easier to just measure off the correct pins on the sender connector while adding one gallon at a time from an empty tank than it will be to actually measure it on the bench.

edit: video works now! And lines up pretty much within tolerances of what I would expect.

 

[Rob Mayercik]

This is correct for 87-90 but for 91-95 it is different. 105 is empty, 5 is full, as I recall.

I finally got to take another look at this yesterday, and since it included pulling out my FSM to double-check the pinout on the connector, I can now confirm that for a 92 (and likely for all of 91-95 as well), you are correct:

0-5 full
66 half
105 empty

Before climbing under the truck I hunted down a 130-ohm resistor to use to "simulate" an empty tank (not exactly 105, but close enough for the purpose).

First thing I did underneath was to put my ohm-meter across the two terminals in the plug from the pump/sender. Got about 10 ohms, which doesn't seem unreasonable for a full tank less about 2 gallons (had the truck out a week previously and filled the tank about 45 miles from home, and gallons/trip meter showed about 16mpg).

Second thing I did was poke the 130-ohm resistor into the matching pins on the body connector, then climb out so I could turn on the ignition briefly and check what the gauge did. Upon ignition-on, gauge immediately dropped down to Empty. That validates that the gauge and body wiring for same are working OK.

Interestingly, at that point I went back to ignition off and reconnected the sender/pump harness to the vehicle harness and turned the ignition on again. The gauge needle went all the way back up to just a hair below Full, which is higher than it was reading the week before (when it still showed slightly over 3/4 full despite being low enough to take on 12-13 gallons at the aforementioned fill-up). The new reading is, like the ohm reading I took of the actual sender, plausible for a full tank reduced by 48 miles' worth of highway driving given that the truck is sitting slightly nose-high and tilted to the passenger side where it's sitting in the driveway.

Maybe all this time the connector wasn't mated properly from when the pump was replaced a number of years ago or the contacts got dirty? I had it off and on a couple times doing the ground upgrade a few weeks back, and that's when it went up a little bit but stayed stuck. I only disconnected/reconnected it once yesterday, but maybe that got the contacts clean enough? The little seal was still on the plug and felt like it was sealing the connector.

Ah, well, we'll see what happens as I run this tank down - if the gauge follows the tank level now, I'll call it a win. If not, there seems to be a good selection of assemblies on RockAuto and elsewhere I can pick from...

Thanks again!

 

[Rob Mayercik]

Update: took the Jeep on a long run last Friday, but the gauge never moved. Doesn't look like I got lucky, so I guess I'm replacing the sender assembly.

There's 6 or 7 brands available on RockAuto (some of which are also attainable through Autozone/Advanced/Napa/etc.) - any thoughts from the community on which brand to get?

 

[Rob Mayercik]

Ended up getting a Delphi, based on feedback from my fellow NAC members.

Now I just have to install it...