Hello all, I'm having a weird problem with the fuel gauge on my 1960 Olds. I have put in a new sending unit in the tank and grounded it to the frame. The gauge is also brand new as well as the wiring. It seems to be reading correctly when the engine is off and key on, but for some reason once I start the car, it reads high. For example, with key on engine off, it reads just over 1/4 tank, which should be about right with the amount of gas in it. Once I start the car it will move up to 3/4 tank. I thought maybe it was a grounding issue so I've been looking at my grounds over and over. I have the three recommended big ones (engine to battery, engine to frame, and engine to firewall). The gauge is grounded to the firewall and I even tried adding a ground from the frame to the firewall gauge ground. No change. Any help or advice would be greatly appreciated.
Sounds more like a 'power problem' (charging system not regulated, or a resistance problem in the long wire lead back to the sender. Attach a cheap volt meter to the wire on the sender. Ground it to your latest GOOD ground. Now, turn key on, read voltage. Record it. Start the engine, and run it up to 2500 RPM. If there's a change in voltage, check up front to another power source, even battery. Check these various points, if the wire to the sender is the only one not consistent, run another wire (test) back and check it again. Sounds like a connector or worn through wire somewhere along the distance back...
Are you sure you adjusted the unit to read correctly? You say you have a new gauge and sending unit. Are they after market or exact replacements? It sounds like it may not be adjusted for the gauge and for the empty and full positions? was it cut to fit the tank? Just throwing this out there.
The sending unit is an exact replacement so should be 0-30 ohms I believe. The gauge is aftermarket and is set to the 0-30 ohm calibration. Sent from my iPhone using The H.A.M.B. mobile app
try disconnecting the other gages in the cluster. my off topic Dodge pickup gages do weird things like that. when the gas tank is full all the other gages read low or not at all when it gets hot [under load working], the fuel gage will read low.
Fuel gauge work with a resistance, usually metered to ground. When you have the engine off you are getting battery voltage, when you start the engine your voltage increases to 13.6 or so. Your gauge is not calibrated properly. Bones
I still wonder if it is not modified for the depth of the tank correctly? If it is reading 1/4 of a tank when it should be reading empty, then an additional 2/4s or a half a tank, when on, that tells me you may have about a half a tank of gas? Maybe it is reading, just not the correct amount because the set up wasn't done correctly when it was installed?
Didn't some vehicles use a current regulator that bolted to the guage terminals.? I think it regulated voltage to 8 volts to feed the sending units. It was a small gold rectangle box.
If it's like the 61 Olds I just finished, it's got a WEIRD fuel sending unit. It actually sends 12 V + to the sender, and gets a resisted voltage back to the gauge. Had nothing but trouble with it. If yours is similar, it could be, as suggested, a generator/alternator voltage issue. Even the factory shop manual wasn't much help "Replace with known good unit".
So this is what I’ve found out so far in my trouble shooting. I pulled out the sending to test it and it is reading correctly the 0-30 ohms. Put it back in the tank and it reads properly. Once I turn the key on and the in tank fuel pump primes, the resistance jumps way up to about 80 or so ohms. Once the pump finishes priming, the gauge needle goes back to where it should be, but the resistance on the meter is still high...turn key off I get about 11 ohms from the sender... Sent from my iPhone using The H.A.M.B. mobile app
One more note, I disconnected the sending unit wire and the sending units is reading 11 ohms with key on Sent from my iPhone using The H.A.M.B. mobile app
I disconnected the wire behind the gauge and it reads 11 ohms. Once I reconnect and turn key, the ohms increase Sent from my iPhone using The H.A.M.B. mobile app
I wonder now if the gauge is doing something similar. After I put everything back together to call it a day. It seems to be working. The resistance is higher when the key is on but looks to be reading correctly...went for a test drive and everything seems ok...fingers crossed it’s working. Sent from my iPhone using The H.A.M.B. mobile app
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