Fuel Guage not working

[Knucklehead]

Background..

1984 Grand Wgoneer. 360/727 fuel Guage did not work when my son bought the truck. The po included a new sending unit like this one


When we did the SOA, we dropped the tank. While it was out, we pulled the sender to install the new one, but it was different. The one we pulled out looked like this one.



The strange part is, the first one is the one listed for 84/85 Grand Wagoneer. The second one, which is like the one we removed, is listed for 86-91 Grand Wagoneers. With the new sending unit, the Guage reads Empty, then as the fuel level drops, the needle starts to move toward Full. My son can vouch that the truck runs out of gas when the Guage reads 3/4 tank. Which freakin sending unit do I need? The Guage cluster is the old style with the round gauges.

[jaber]

It sounds like a PO swapped in a later tank. You might have to find a pre '86 tank for the right sender to work.

If theres a trick, someone will pipe in.

[Knucklehead]

The new sender we put in (the first link above) works and is the correct one according to Bj's but the gauge works backwards and is way off. That would have nothing to do with the tank being out of a newer truck. When we pulled the old sender, you could tell it had been in their for a while (read that as years) due to all the dust/dirt/crud. I am wondering if someone had swapped in an older gauge cluster. I think I remember reading that they changed the polarity on the gauge, but am not positive that's the case.

[jaber]

I think I remember reading that they changed the polarity on the gauge, but am not positive that's the case.

Yes they did, I thought it was when they changed the dash styles. I could be wrong.

[carnuck]

I think I remember reading that they changed the polarity on the gauge, but am not positive that's the case.

Yes they did, I thought it was when they changed the dash styles. I could be wrong.

That's my recollection too. Maybe the original tank was leaking and was swapped out for a newer one? Older sender should fit the newer tank. Just the wiring in it was reversed.

[AwesomeJ10]

Have you used a volt meter to test continuity all the way from the sender to the gauge? One connector on the back of the gauge should receive 12V + when you turn the key on. The other connector (on the back of the gauge) should receive ground when you move the sender up and down. You measure this amount of ground the gauge receives from the sender in ohms.

[Knucklehead]

Have you used a volt meter to test continuity all the way from the sender to the gauge? One connector on the back of the gauge should receive 12V + when you turn the key on. The other connector (on the back of the gauge) should receive ground when you move the sender up and down. You measure this amount of ground the gauge receives from the sender in ohms.

I have not as of yet. We do have another gauge cluster we can try, since the cluster has to come out anyway to check continuity, to see if acts the same with a different gauge. At any rate, the sending unit we have now matches the gauge cluster year wise...at least according to the part descriptions on BJ's website anyway.

[Knucklehead]

Ok, i think i figured out how the other sending unit got in there. I went to O'Reillys web site and looked for a sending unit for a 1984 Wagoneer and this is the one they list.



Oh...and its $92. Time to do some testing this weekend.

[carnuck]

You can check by putting resistors in line with the wire for the sender to ground and reading the gauge to see if it's accurate

[babywag]

I think I remember reading that they changed the polarity on the gauge, but am not positive that's the case.

Yes they did, I thought it was when they changed the dash styles. I could be wrong.

That's my recollection too. Maybe the original tank was leaking and was swapped out for a newer one? Older sender should fit the newer tank. Just the wiring in it was reversed.

They didn't change the polarity of the gauge, they work off resistance not voltage.
The sending unit is just a variable resistor, the wiring is not "reversed".

Newer '86-'91 fuel senders have the opposite resistance values as earlier ones.
Empty = 1 Ohm
1/2 tank = 44 Ohms
Full = 88 Ohms

Older '80-'85 fuel senders are the opposite.

I'd guess the gauge was swapped or they re-lettered it to match the newer sender? Snap a picture of the fuel gauge.

The older sender should read ~10 ohms when full & ~70 ohms when empty, you can check it with a voltmeter on the sending unit wiring connections.

[yjsquareguy]

Thank you all for the detail. This is great. My son and I just bought a 1989 Grand Wagoneer and have the "Fuel gauge not working" problem. This is very helpful information.

[Gumby]

I swapped out my older sending unit for a new one from Amazon (way cheaper than the box store). Well it always ready differently and only when it wanted to. I would have a full tank it would read no more than 3/4 then it went to E and stayed there. So I cleaned up the old one put the sock from the new one on and now my gauge tells me how madly in love with the gas station my waggy is .

I would look for an old one and clean it then slap it back in.

[malcoll]

OK... so I am working on my sons 1990 GW...... I don't think the fuel tank has EVER been out for a number of reasons... but when I pulled the fuel sending unit it looks like the one listed for the "up to 1985"... the resistor portion is at the top not further down on the assembly like what is shown above for the later style. The gauge worked properly (except needed a new "sock")...but in messing with it I broke it and now need a new one... which one do I order from TGW???

[Stuka]

OK... so I am working on my sons 1990 GW...... I don't think the fuel tank has EVER been out for a number of reasons... but when I pulled the fuel sending unit it looks like the one listed for the "up to 1985"... the resistor portion is at the top not further down on the assembly like what is shown above for the later style. The gauge worked properly (except needed a new "sock")...but in messing with it I broke it and now need a new one... which one do I order from TGW???

The polarity changed on them as I recall. So with a full tank, it will show empty, and vice versa.


Sent from my iPhone 6 using Tapatalk

[x98boardwell]

I purchased on from AutoZone for my 1984 GW and it didn't work. I purchased another one from BJ's and it worked fine and looked different. Can't remember by looking at your pic's which one mine looked like but clearly it said it was for an 84 and didn't work... so Autozone was wrong.

[j2sax]

SO what should the Ohms reading be for the later 86 and up sending unit? THanks!

[babywag]

SO what should the Ohms reading be for the later 86 and up sending unit? THanks!

Empty = 1 Ohm
1/2 tank = 44 Ohms
Full = 88 Ohms

[FSJRomanGladiator]

Hey ya'll. new to the family and restoring my 74 J10. Pretty stoked, picked her up in December.

As we all know, restoring can be fun, exciting but expensive and frustrating b/c parts are hard to find. I need everyones help, as everyone prob faced this already.

New tank and hoses are waiting to be installed, but the sending unit wire that connects to the gas gauge, i can not find to purchase.

Any help would be much appreciated.

[tgreese]

Are you missing the wire? That wire is part of the complete harness that supplies the entire rear of the truck. Unlikely you can purchase that part. Normally you would repair what you have.

Here is a post that may help you - https://www.jeepforum.com/forum/f8/basi ... d-1340134/

[letank]

Hey ya'll. new to the family and restoring my 74 J10. Pretty stoked, picked her up in December.

As we all know, restoring can be fun, exciting but expensive and frustrating b/c parts are hard to find. I need everyones help, as everyone prob faced this already.

New tank and hoses are waiting to be installed, but the sending unit wire that connects to the gas gauge, i can not find to purchase.

Any help would be much appreciated.

The wire is somewhere around the frame, then test and connect it as mentioned above by Tim. The gas tank is metal, or was metal, and it has to be properly grounded, rust is a poor conductor, sanding of installing an extra wire between gas tank and frame.

On my last project, I found the wire cut off at the harness... added an extra length to a good ground et voila, gas gauge works...