Just purchased a '69 Cutlass convertible in nice shape. Gas gauge does not work so thinking of looking toward the sending unit as the culprit. Question is does the tank need to be dropped to access the sending unit or is there another way?

Thanks

 

Congrats on the purchase. Yes, the tank needs to be dropped to access the sender. I don't know about you, but I'm really lazy. I'd try troubleshooting the problem BEFORE going through all that trouble. There are a whole lot of potential causes that don't require dropping the tank to fix them.

 

One of the most common problems causing an inaccurate gas gauge is a poor ground. You can access the ground wire from beneath the car without dropping the tank. It will be a wire running from the fuel sending unit to the underside of the body or the frame. Make sure the connection is clean and well terminated (i.e. a terminal end that's well crimped or soldered with heat shrink).

 

When you turn the key on is it pegged passed full or pegged empty?

 

I redid the ground to make sure it was good but that made no difference. When turning the key on the
needle does not move. I've attached a pic showing where the needle is no matter what I try so far.

 

You have an open circuit, chances are your sender is bad. If you ground the sender wire it should drive the needle to E with the key on.

 

That periodically happens on my car, so I grab the brown wire behind the gas tank,wiggle it, and the gauge starts working again - for a while.

I had the same issue on my 70 Supreme back in the 80s and discovered the sending wire was loose where it connects to the stud on top of the sending unit on the tank. I crimped the connector so it was tight and never had that problem again. Now I'm too old and lazy to drop the tank, so I just pull on the wire when the needle goes to the HOT light.

 

X2 you can also get a new unit and test your ohms with the wires from the tank if it all works out of tank then it's the unit in the tank.

 

Ok, I grounded the sender wire and, like you said, needle went to E with the key on. Looks like tomorrow I'll be draining the tank and dropping the tank. Will order a new sender today from a local parts store.
Thanks for your help.

 

 

Glad we could help you identify the problem. It's sort of a PITA to drop the tank but while you have it down you MAW invest in one of these kits:

https://www.summitracing.com/parts/sum-900056-3

 

Ummm, whats PITA about dropping tank? Very straightforward and easy.

 

Well, other than the fact that the nuts are always rusted to the long bolts that hold the straps, so you have to cut them and get new ones...

 

Ah, you have rusty cars That explains

 

And having to drain the tank, first, which is not always simple.

And having to crawl under the car and maneuver this large, bulky thing around and hold it in place while reattaching it.

I've dropped and replaced tanks on two cars now, and neither was a walk in the park. I got it done without a problem in each case, but it's not something that a typical do-it-yourselfer who has only a floor jack and jack stands wants to do on a regular basis.

 

x2

 

OK. Dropped the tank and replaced the sender. Waiting for my son to help put it back in this weekend so will up date you then whether that solved the problem.
And yes, it was a PITA even with a lift. Naturally the bolts were frozen so even soaking them overnight still had to CAREFULLY cut one off. Got it all cleaned up and ready to go back in.

 

Check the connection in the trunk and the sender ground wire first.

There is a good troubling shooting guide in the CSM.

 

Before buttoning everything up, make sure the sender arm travel is basically the same as the one your replacing. This way the gauge will be as accurate as the original.

 

Son had the flu so put it back in myself. Kind of a struggle for a 72 year old but managed. Nice to have the lift. Everything hooked up and turned the key on and- what do you know- it works! Whole problem was the sending unit. Gave me a chance to look inside the tank and see that it was very clean and clean up the outside and paint it before reinstalling. I appreciate all the recommendations and comments. Great group of people.

 

Sure it is, especially when you put a jackstand through it....