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I bought a 69 cutlass station wagon late summer of last year.
The fuel gauge has read past full ever since but it still seems to work. (moves as fuel is used or when I fill up) I have been scared to see if it will go all the way to the E as when I have the tank full it is so far past F. I have seen the posts on here about bad ground wires and loose connections but from what I was reading the gauge seems to stay at E or way past F without change where as mine is changing.
Any ideas on this issue before I try removing the tank to check connections as I know that the tanks on these wagons are not easy to remove and put back.
From reading on some other posts I saw that there are 30 and 90 ohm systems. my thought is that the previous owner may have put in a 90 ohm sending unit and left the 30 ohm gauge? I know that replacement parts like this are not easy to find for the wagon specific tanks so maybe they found one that fit and just used it because they knew and didn't mind.
You 69 wagon should be a 90 ohm sender. If you can (station wagon tanks are a bear) remove the sender wire and ground it with the key on, the gauge should go all the way to E, with it disconnected it should go past F. If your gauge does this then the wiring and gauge is good. Remove the tank and check the sender.
From reading on some other posts I saw that there are 30 and 90 ohm systems. my thought is that the previous owner may have put in a 90 ohm sending unit and left the 30 ohm gauge? I know that replacement parts like this are not easy to find for the wagon specific tanks so maybe they found one that fit and just used it because they knew and didn't mind.
All fuel gauges were 90 ohm from the factory. My guess is either the sending unit or the dash gauge is at fault. Short of replacing the dash gauge or the sending unit, your best bet, I think, is to do what Koda says and determine what the gauge reads when the tank is empty or nearly empty. Then live with it as long as it reads consistently.
There is a troubleshooting procedure in the '69 chassis service manual, but it requires one of the special tools the manuals are always referring to.
New sending units are not readily available for station wagons, in my experience. Replacement dash gauges can probably come from any A-body Olds from those years, I would think.
Not uncommon, in my experience, for a fuel gauge to read past full. Since you say the needle does move I would:
1. Determine capacity of gas tank.
2. Drive until gauge reads half full (E---|---F)
3. Fill tank, noting number of gals.
4. Is the number of gals. close to half of the capacity?
5. If so, you are good to go!
6. If not, resort to "Plan B," as advised by others, above.
Tested the lead as suggested and have continuity from sending unit end of tan wire through the flat ribbon harness under the carpet and out the end of that harness and through to the tan wire out of the male connector. Then grounded as suggested with key on and needle did not move off of the "over" full mark. No movement at all. I cant even begin to see or feel the end of that tan wire to see if it is even connected to gauge. Which begs the question of what does gauge read if tan wire is not even connected to gauge? Then I added about 2 gallons of gas and that told me the tank was not full and over flowing. By the way it looks like the tank and sending unit has been replaced
Last edited by Rocket Olds; March 30th, 2018 at 02:41 PM.
Reason: more info needed
Then grounded as suggested with key on and needle did not move off of the "over" full mark. No movement at all. I cant even begin to see or feel the end of that tan wire to see if it is even connected to gauge. Which begs the question of what does gauge read if tan wire is not even connected to gauge? Then I added about 2 gallons of gas and that told me the tank was not full and over flowing.
What, exactly, did you ground? It has to be the wire from the gauge, not the wire from the sending unit. Also, the wire must be connected to the gauge, and you need to verify that it is if you're not sure.
If the tan wire is disconnected from the gauge, that's an open circuit (infinite resistance), and the gauge will read Full or well past Full with the key on. Grounding the wire makes a closed circuit of zero resistance, so the gauge should go to E with they key on. If the gauge does anything other than these things, there is a problem in the wiring from the gauge to the sending unit.
Maybe I was unclear as to what I understood I was supposed to do, it was the tan wire that runs from the gauge to the flat harness that goes under the carpet to the back seat area and then again appears as the tan wire that goes to the sending unit. NOT the ground wire off the sending unit. At the tank end of that tan wire I unplugged it from sending unit and grounded it , the tan wire, with switch on and no movement of needle. Was that correct? (again I had continuity from tank end of that wire through to where it appears out the dash end of the flat harness). That is what prompted the question of what will the gauge read if tan wire is not connected to the gauge. and you answered that part for me. Now I need to verify that it was connected to gauge in order to verify my test results. I will do that and report back maybe tomorrow. Thanks for your time, Mike
Last edited by Rocket Olds; March 30th, 2018 at 03:47 PM.
Reason: added info
Let's try this. Here's a little diagram I made of the fuel gauge circuit. It's very simple. The upper diagram shows the intact system.
The second diagram shows the first test to make. Disconnect the wire from the gauge to the sending unit. There is usually a connector that you pull apart somewhere along the way. It's often in the area behind the license plate, possibly in the trunk. Ground the side coming from the gauge, and turn the key ON. The gauge should go to E as shown.
The third diagram shows the second test to make. Remove the wire from the sending from ground. With the key ON, the gauge should go to F or past it.
If the gauge does not do these things, there is a problem in the wiring from the gauge to the connector or in the gauge itself. If the gauge does pass these tests, then it's time to check the ground from the sending unit (shown far right). It should be clean and tight. If that checks OK, then the problem is the sending unit itself or the wire from the sending unit to the connector.
I don't know about specific wire colors or wiring harnesses or whatever. No matter how the wires are specifically arranged or what colors are used for them, this is the basic circuit.
Thank you. I think that is what I did. On 67 CS there is no connector near the license plate area. the gas gauge wire (tan) runs direct from gauge and connects to the flat ribbon harness under front edge of the carpet and goes on under the carpet to the back seat area and comes out of the flat harness as a single tan wire underneath the car that is directly connected to the sender and I checked and I have continuity all the way from sender end of the wire through the flat harness to where that same wire comes out at front floorboard to go to the gauge. Also, I had already re-routed and checked the sender ground wire first thing to give a good ground before going to this thread. What is wrong with my gauge at this point is in your #2 diagram. That is what I did and no response from gauge. But as I said before I will make sure the wire is attached to gauge which is your #3 and report. thanks for your patience, Mike
Well I have been educated and updated as I discovered that the 67 A-body models gauge package has a circuit board with multi-pin connector. My 65 GTO was different. Well the main harness for the gauge cluster is attached which explains why everything else works. Only the gas gauge seems to be the problem. So now that I have established that grounding the gauge with key on changes nothing and the gauge shows over full all the time where do I go from here? Any and all suggestions will be welcomed. Thanks, Mike
FYI, I mentioned in post #10 that the tank and sender looks to have been replaced. Can you put the sender in upside down which then in essence shows full all the time? remember this is a CS where the sending unit is placed at the rear of tank just above the seam. I don't want to drain the tank unless I have to so I thought I would ask that simple question. My thinking is that the circuit board should not go bad. or is that a common problem that you guys see and I am not familiar with? thanks again Mike
You've already proven there is an issue with wiring (open circuit) or faulty gauge when you grounded the tan wire and nothing happened. I don't think your current issue is the sender. You need to troubleshoot the instrument cluster.
Well I must have been drinking my bath water again cause I finally realized what I said in previous post about the sending unit maybe upside side down and it hit me that I had the unit out of the loop when testing the gauge and it not responding, DUH!!! So by all accounts it is most likely the gauge. I know I have continuity in the wire up to but not including the connector that plugs into the circuit board. Shy of taking the dash apart is there a way to test the circuit board or get to the gas gauge or can the gauge even be replaced? Once again thanks to all, Mike
Been trying to check thru posts to find best way to get to circuit board. Noticed you have a 67 also have you taken out the board or whole assembly before and if so what is the best way?
g,
I read most of the responses but might have missed one. If so, sorry if this is a repeat.
Since 1967 I have owned 12 GM vehicles, all purchased new except for my first one and my 84 S-10. I also had 3 GM company cars when I worked for Xerox years ago.
Everyone single one of those vehicles always read well over the full mark when filled up. The gauge stays there for quite a few miles and then starts coming down. They will typically go right to the "E" mark without running out of gas.
Personally I don't think there is anything wrong with yours at all. Run it down to 1/2 tank and then fill it up and see what it takes to fill it. That will give you an idea for sure.
Bill, did you read the part where he grounded the lead to the fuel sender with the key on and the gauge did not go to E? No his issue is not normal.
Actually I do not see any responses from the original poster unless I am truly blind. I just looked again to make sure. Several replies have suggested that but I have not seen where he actually tried it.
He says his gauge is going down but he is afraid to let it go all the way to empty. Sounds like a typical GM gauge to me.
You are correct Bill, the OP has not checked back since he started the thread. I also believe his fuel gauge is working correctly. Ordinarily I would separated them into 2 different threads, but both posters had similar problems, with the same troubleshooting steps. So we walked "Rocket Olds" through some steps to isolate his issue. I was hoping the OP would have reported back, but it is a holiday weekend.
March 29th, 2018, 06:52 AM
