I have the same kinda thing happening. Except, my rear tank reads fine and my mid (front) tank doesn't. I replaced the sending unit with a Spectre unit. It work properly for two days. Then it worked like a tachometer, sat on "E" at idle and went towards full when I gassed it. That lasted for 2 or 3 days until it just stays at "E" now. After a lot of reading from multiple forums, some say it might be from the selector switch on the dash. The electical signal goes through that before it gets to the gauge. Might be worth testing. I'm too lazy to mess with it in the winter months. When it warms up, I will test mine.

 

Mine will always switch the tank, but sometimes the gauge does the same thing until you wiggle the switch up/down a few times, then it starts climbing. I think I'm honing the contacts in, though, it happens less and less often. I really like problems that heal themselves......

 

Good thoughts there Jake and Slik. I'm gonna try wriggling the switch, then probably bypass or replace it. But I don't think that's it, because I've put both connectors on both tanks....forward tank reads accurate with either connector, rear is inaccurate with both. Who knows, maybe I got three bad sending units in a row. I did try running my borescope into the tank but couldn't see anything. I tried several times but got nervous about possible combustion each time and pulled it out. Those LED's might ignite fumes. I don't want to be the dead guy everyone tells stories about......"Hey, did you hear what that ******* did?"

This may be a blessing in disguise. I've toyed with the idea of making a 30 gallon fuel cell, with top entry marine type sending unit and separate pickup. Maybe I should brush up on my aluminum TIG welding skills.

 

I have a question. Don't mean to hijack but it is about the fuel gauge also. 79 f150 factory duel tanks. Neither tank will read on the gauge. I crawled underneath and both sending wires had been repair mulitpul times. I went to the jy and procured replacement wire and connectors. "Bench test" Ran continuity test from tank connector to ground ring terminal. GOOD. Ran continuity from tank connector to bullet connector. GOOD. Tried grounding the wire harness to get the fuel gauge to move. NOT. My oil pressure and temp gauge work.
Will it hurt anything or ruin the fuel gauge if I ground the gauge itself to be sure it works properly? Is there a separate IPVR for the fuel gauge or is it the same one for the oil pressure/temp gauge? I have roughly 5 gallons in each tank now. That should be enough to give a reading on the fuel gauge isn't it? Is there something on the frame rail switching valve I should look at? The switch valve will switch between the 2 tanks.
I have to leave Friday (16TH) for a 20/hr drive and having a working fuel gauge would be nice.

Thanks to all who came before me/us for having a very informative web site.

 

Good so far. Especially considering the PO splices.

Grounding from where to where?
Are you sure you still have a good body ground directly from the battery to the body? And added one to the frame just for good measure?

As long as you don't leave it grounded for long, you should be fine. Stock gauges are dampened anyway, so the needles don't just instantly peg, so the delicate needle itself won't be damaged.
But you've already determined the wires are good at least to the plug. Where's the plug? If it's before the tank selector switch (which I'm assuming it is) then the next suspect you have not tested yet is the switch itself. And it's a very common source.

Nope. Same one. So if the other gauges work, then the IPVR is working.
Only one it's not controlling is the ammeter.

Well stop dilly-dallying then! Go fill up at least one tank, but since this is a test and you're going on a trip anyway, the only way to know short of pulling the sending unit is to fill the tanks with more than 5 gallons. Because no, you can't always count on that being enough.
The larger the tank, the larger the "reserve" amount. And five gallons on a big tank is not that much more than the normal three gallons. Well within the range of an old tired gauge system.
And speaking of the senders, you have not tested them yet? First thing to do before filling up in fact. The standard ohm range is approx 73-10 ohms. If your unit is sending out an EMPTY signal to the gauge, you will read it as being at or near the 73 ohm mark. If it's close to, or over that, then it's not the gauge or related wiring that's at fault. It's the sender or the amount of gas you really have in it.
Are you sure you have five gallons?

I believe yours should have the simple 1-wire solenoid type valve, correct? If so then no, as long as it's switching the tanks and you're hearing the click when it changes back and forth, the valve itself is functioning as expected.
But along the frame rail are many points at which the wires can become deteriorated. Or worse.
Luckily though, it doesn't sound initially like it's any of the wiring between the tanks and the connector.
But it can't hurt to hunt along there.

Very nice indeed! But I would test the senders first, then just fill the tanks next.
Then, if you don't find the gremlin, go on your trip and pay close attention to the miles traveled. Figure on 8 or 9 mpg, vs whatever capacities the tanks are. Keep a log so you don't have to memorize every waypoint during the trip, and stop before you get to the limit.

Good luck!

Paul

 

Well, no luck so far. And nothing will probably change over the next two months because Turkey Season opens tomorrow! And then I'll hunt a few other states after our closes in May. No time for working on play vehicles unless it's necessary. I can live with no fuel gauge that long. We'll figure it out in June.

Thanks for all the help guys!

 

I would say the float arm needs adjusting g but you say it worked after installed for a little bit. Got me stumped...

 

Pardon me Lukas, but what were we talking about? I had something else on my mind.......

 

You gonna hide behind the decoy?

 

Not a big decoy fan.

 

Well, I changed the tank switch and the pigtail. No change. I do have a spare used gauge laying around somewhere. Guess I'll try that next.

 

Ranger,

Here's an easy test that will only take a few minutes...

You say you've replaced this sender more than once? If you still have the bad senders, grab an ohm meter. If you don't have one, you can likely get one under 20 bucks at Radio Shack (if you still have one) or maybe at Autozone/Oriellly's/Pep Boys. You're not trying to troubleshoot the Space Shuttle here, so a cheapie is just fine. Digital or analog will do... and set it to a low ohms scale. Connect the leads to each contact on the sender and watch the reading as you move the sender arm through the whole range. You should see a somewhat steady increase/decrease of reading on the meter. I ran tests on my Aux tank sender after repairing it.... seems I recall it gave a reading from 0 ohms to 80 or 90 ohms. If you have more than one sender on the bench, make comparisons. I still have an old rear tank sender out in the garage, so I will go see what the reading is on it later and get back to you on that. If you don't get a similar reading, or it does not increase/decrease with the full sweep of the arm, then the sender itself is indeed the problem.

IF it turns out the sender tests bad, and since it sounds like you have many "used" senders now in your possession, I would carefully take one apart and see what is going on in there. With needle nose pliers and a flathead screw driver, you can bend those tabs on the cover up and open it up. You will see a coil of wire in there with a swiper on it that rides up and down on the coil... changing the resistance as it moves. If there's something funky going on in there, you should be able to see what it is. Look for garbage or rust in there that could cause a problem.

If your ohms tests shows a nice steady increase/decrease through the whole range of the arm sweep, then your sender is fine and the problem is elsewhere.

My guage was reading bad due to the sender being all corroded. I cleaned out the inside where the contacts are made and put it all back together. Has worked perfectly now for the past 4 months.

 

I just went and checked my spare sender. With the float arm in the "empty" position (float is inline with pickup tube/sock), I measured 76 ohms. With the float in the "full" position, I measure 14 ohms. Let us know what you get on your senders.

 

That's very close to the "official" range of 70-10 ohms.
The actual readings as specified in the old books was something like 9.6 full and 71.2 empty, or something like that (I just made up the numbers, but they're probably close) but since every gauge and truck's wiring condition could vary, it's best to check them on the truck.
So once you verify that the sender is somewhat within range, hook it up to the sender wire back at the tank and keep testing.

Paul

 

Well I'm still operating without accurate fuel reading, and now that I've ruined my fuel mileage by installing a new camshaft, I think I'll need to make that fuel cell. 35+ gallon probably. I'd like to use factory fuel gauge in the dash. Can someone tell me the ohm range so I can match up a sending unit? Thanks