[JT42]

So I am ordering a new gas tank on Monday from Classic and I am wondering if you guys usually replace the sending unit at the same time or if its working do you just re-use the original? Not sure if those are prone to wear out and if I already have the tank out I want to do it right the first time.

Also I plan to install an Auto Meter fuel gauge in the coming months so is there anything I should do while having the tank off to prepare for that?

 

[slickman]

Its good practice, if it were me I would not just replace the tank, do both.

 

[Custom Jim]

With a gas tank assembly you have the tank, sending unit, wiring, and gas tank straps, not to mention nuts and bolts which could all be replaced but would any of the new parts be better than what you have ?.
I've read and replied to many threads about persons replacing a gas tank and some have reused combinations of old and new parts while others have bought all new parts only to have problems. Sometimes things go smooth and persons reusing some of the old parts have not had problems but others have been in a nightmare.
Unless you have a lot of time to burn and possibly extra money, look and test what you have and get an idea what kind of shape it's in and then weigh out if you would want to reuse an old part or replace it with a new one.
In a perfect world all replacement parts work as designed but things are not that way.
If I had a new sending unit I would get out my meter and make sure it works as it should as far as the resistance measurments with the float arm at the full up position, full down position, and then possibly do some checks with it a quarter of the way up, halfway up, and three quarters of the way up. Doing a simple test like this allows you to know, or be more sure later, that if there is a problem at least this was checked and can be pretty much taken out of the equation for some other troubleshooting if needed later.

Jim

 

[JT42]

With a gas tank assembly you have the tank, sending unit, wiring, and gas tank straps, not to mention nuts and bolts which could all be replaced but would any of the new parts be better than what you have ?.
I've read and replied to many threads about persons replacing a gas tank and some have reused combinations of old and new parts while others have bought all new parts only to have problems. Sometimes things go smooth and persons reusing some of the old parts have not had problems but others have been in a nightmare.
Unless you have a lot of time to burn and possibly extra money, look and test what you have and get an idea what kind of shape it's in and then weigh out if you would want to reuse an old part or replace it with a new one.
In a perfect world all replacement parts work as designed but things are not that way.
If I had a new sending unit I would get out my meter and make sure it works as it should as far as the resistance measurments with the float arm at the full up position, full down position, and then possibly do some checks with it a quarter of the way up, halfway up, and three quarters of the way up. Doing a simple test like this allows you to know, or be more sure later, that if there is a problem at least this was checked and can be pretty much taken out of the equation for some other troubleshooting if needed later.

Jim

Thanks for the advice! Is there a thread about how to test this? I dont drive the car regularly so its ok if it is out of commission for a while. I could pull the old tank off and check the resistance on the old sending unit to see if I could just use it but I am not sure how to do that.

 

[veno]

remember... OEM is best.... and I tool would rather have the OEM sender.. if its working correctly.... the OEM stuff usually out preforms aftermarket stuff in terms of longevity..

 

[tnblkc230wz]

If the sender is working leave it alone. It isn't that hard to pull the tank.

 

[1quik69]

If the original sender was working ok I wouldn't change it. I replaced the sender in mine when i put in the new gas tank and it only reads half full when the tank is full. Looks like i will be pulling my tank when it gets low on fuel.

 

[onecarnut]

If you plan to change the gas gauge at a later date, just remember that they have to be compatible.

That is why most aftermarket gas gauges will come with a sending unit.

Original components have worked best for me.

 

[74 hatchback]

I strongly believe if it aint broke dont fix it!

 

[JT42]

So I am sorry I didnt give full info because I am new to this area and dont really know how the gas gauge/sender works but the stock gauge does NOT work. I dont know if its the gauge, the wiring, or the sending unit though.

Is there an easy way to test these?

Like I said I plan on getting an Auto Meter gauge and it looks like that will be part number 4314 which is the 0-90 ohms which should be stock.

 

[taz3]

Is it reading full or empty? Full ready usually means a bad ground or the sending unit isn't getting power,(my car does this, I just wiggle the wire and it works, it needs to be crimped tighter) empty reading usually means the gauge is bad. This is not the written in stone, but a good starting point.

 

[JT42]

Is it reading full or empty? Full ready usually means a bad ground or the sending unit isn't getting power,(my car does this, I just wiggle the wire and it works, it needs to be crimped tighter) empty reading usually means the gauge is bad. This is not the written in stone, but a good starting point.

Really? It reads past full actually. The needle is as far as it can go past full. Which ground might I need to check? Is there a ground from the gauge itself or a ground by the gas tank for the sending unit?

 

[taz3]

Really? It reads past full actually. The needle is as far as it can go past full. Which ground might I need to check? Is there a ground from the gauge itself or a ground by the gas tank for the sending unit?

Yes, if you climb under the car with a light you should be able to see it or you may have to lower the tank to see if it's broke. I'm a small guy so I fit!

The ground come from the sending unit to the body, sorry I don't remember where though. They usually break at the sending unit, so you may see a black wire hanging down.

 

[tnblkc230wz]

The sending unit is very easy to test. The sending unit wire is connected to the rear harness inside the trunk right next to the trunk latch. There will be two wires in the connector. one is the fuel gauge and the other is for the license plate light.

First make sure the ground wire to the sending unit is in good shape. With the car almost out of gas, find the fuel guage wire inside the trunk. Put an ohmmeter on it and the other end to a good ground. It should read close to 90 ohms. Then fill it up and take another reading. It should be near 0 ohms.

The sending unit is a pretty simple device. The biggest malfuntion is a dirty, rusted ground wire.

 

[JT42]

The sending unit is very easy to test. The sending unit wire is connected to the rear harness inside the trunk right next to the trunk latch. There will be two wires in the connector. one is the fuel gauge and the other is for the license plate light.

First make sure the ground wire to the sending unit is in good shape. With the car almost out of gas, find the fuel guage wire inside the trunk. Put an ohmmeter on it and the other end to a good ground. It should read close to 90 ohms. Then fill it up and take another reading. It should be near 0 ohms.

The sending unit is a pretty simple device. The biggest malfuntion is a dirty, rusted ground wire.

Awesome info, thank you! I will check that out tomorrow and see what I find out

 

[tnblkc230wz]

Awesome info, thank you! I will check that out tomorrow and see what I find out

I may have the readings backwards, but the test is corrrect.

 

[JT42]

So I cleaned up the ground wire contact spot first as it was definitely rusty so that looks a lot better. I also traced the wire from the tank to the harness next to the trunk latch like you mentioned and it appears in good order.

However when I try to test the ohms I am not getting a reading at all. Does that mean I dont have a good enough ground for the multimeter? Or could it be that the sending unit just isnt working? Also the car shouldnt have to be running correct? I have the key in the on position so it should be getting power

 

[BigMike]

This is very timely information. My gage reads full when I fill it, then when it gets to 3/4 tank it hangs there until it get to about 1/4 tank then starts reading again. Thanks for the rundown on diagnosis.

 

[burns]

This is very timely information. My gage reads full when I fill it, then when it gets to 3/4 tank it hangs there until it get to about 1/4 tank then starts reading again. Thanks for the rundown on diagnosis.

I call that "the chevy half" I think every chevrolet I have ever owned has done that.

 

[69AKDN]

So I cleaned up the ground wire contact spot first as it was definitely rusty so that looks a lot better. I also traced the wire from the tank to the harness next to the trunk latch like you mentioned and it appears in good order.

However when I try to test the ohms I am not getting a reading at all. Does that mean I dont have a good enough ground for the multimeter? Or could it be that the sending unit just isnt working? Also the car shouldnt have to be running correct? I have the key in the on position so it should be getting power

If you want to test your sender do it while it's out. They are most likely 90 ohms ( it will be marked ), put one lead to ground on the sender and the other to the insulated terminal of your sender which goes to your fuel gauge...swing the sender through it's full range, it should go from 0-90 ohms..smoothly. The sending unit is nothing but a variable 'ground' so to speak...so there is no power there.