73 Gauge Issues

[Bucky]

My fuel and temp gauges are not working properly. I checked them with a ground wire and turned on the key, both functioned properly. I replaced both sending units. The temp gauge moves to just above the 120 mark when it's hot and the fuel gauge only reads 3/4 when it's full. I also replaced the voltage regulator behind the dash.

Any ideas of whats wrong?

 

[Gibber]

When you say you grounded them and they functioned properly....when you remove the sending unit wire and ground it, do the gauges try to go full scale high? If they do, it still could be a voltage limiter issue...unless you are using a Real Time Engineering solid state limiter....seems like if both of those thermal gauges read low it may be a less than 5V output from your voltage limiter issue...my idea anyways...

Mark

 

[BillGrissom]

Your question concerns calibration, not function, so you need to do more than just ground the sender wires. Install a resistor of known value and compare to the factory readings expected. Before that, do as Gibber suggests and verify your Vreg does output 5 V. Did you replace it with the factory can or an improved electronic one?

If you don't want to do any of that, get a red marker and draw a line on the gage front when the tank is full and mark it "F". That is how a true CMB would fix it.

 

[Bucky]

They both did go high on the scale when I grounded them. I am not sure on the VReg. I got one from the local Carquest store, I assumed they were all the same. I checked the wires at the sending unit and at the gauge cluster with a test light. The light pulsated on and off. Is that normal?

 

[TrailBeast]

The pulse is a normal fuction of the regulator, thats how it regulates (on-off-on-off)

 

[2 Darts]

Here's my 2¢ worth for the discussion. Check the wire harness connection at firewall. Clean both the harness and the socket connection thoroughly. In fact, doing this on all connections will make electrial accessories throughout the car work better.

 

[67Dart273]

You have to think of this as a "system."

ARE the gauges in calibration? (HOW old are they, again?)

ARE the sensors in calibration?

Power, wiring, connections

Here's a roundup of just some of the problems on my 67

The VR was bad

The VR socket connections, which are brass spring fingers, were NOT contacting the PC board reliably, and I had to solder jumpers from the brass fingers to the PC board

The board harness connector was AFU, corroded, broken pins

The nuts on the gauge studs were not making reliable contact with the board

The temp sender was bad

The temp sender wire was corroded where it feeds through the bulkhead connection

You can check gauge calibration AFTER you've gone through all of above, with resistors. The sender resistances, for temp or fuel are the same:

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

You can substitute those resistors for the sender, give time for the gauge to stablilize, and check cal. I would do this with the engine running, as the system runs at 14V, not 12, and this would "make certain" that the gauge VR is working OK

RTE makes a well respected replacement VR:

http://rt-eng.com/rte/index.php/Main_Page

 

[Bucky]

I will give the RTE regulator a try. Thanks for the advice. All the other connections are solid.

 

[Bucky]

You guys are awesom. The real time eng. VR worked my gauges now read correctly.

Thanks a bunch.