Gauges Peg Max

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Renegade

Renegade

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Jul 13, 2008
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Location
Centennial, CO
67, Barracuda

The fuel, temperature, and oil pressure gauges all max out when the car is on. Is this due to a faulty voltage resistor and or ground?

Also, if that voltage resistor is not hooked up to the back of the fuel gauge can that distroy all three of these gauges? I think I may have fried them.

Thanks
Josh
 
yes and yes you did, answer your own question. you may get lucky, and they will still work, good luck.
 
Well if they still go full scale when you turn the power on I would say they are not fried.

The instrument voltage regulator is built into the fuel gauge on your car. You will need to pull the cluster and take the fuel gauge apart so you can isolate the contacts. I put a piece of mylar between them and tacked inplace so it wouldn't fall out with some super glue.

You can either build it yourself or buy one of the solid state regulators you see advertised here or other places on the web. I made my own from a 7805 5volt regulator IC and mounted it on a heat sink attached to the frame of the dash cluster. It's been working great since 2001 (and 60K+ miles).
 
One of my customers claimed he could disable the limiter by removing the turn signal fuse. I dont know if that is common , correct, or if his car had some crossed wires.
I guess I should know where that 12 volt supply is tied in but I dont.
Reason I mention this is so you can try it if you like. If that 12 volt supply cant be interupted, you would need to pull all 3 sender s connecters to protect the gauges until the panel is pulled for repairs. Good luck and let me know if I can help.
 
My temperature gauge started doing that the other day; pegging out at high temp reading when I turned the ignition switch on a stone cold engine. Everything else is fine, so I must have a short somewhere.
 
Wild pointer swings is another indicater of a bad limiter. Pointer will race to max then drop right back to a somewhat normal position.
 
Wow guys, thanks for the replies.

So if the gauges are fried, then they wouldn't display any information? Or they would still peg max if they are fried?

Thanks
 
If they still move to full scale when power is applied they are not fried. These gauges weren't accurate when they were new and driving them to the stops may make them less accurate but what you are looking for from the factory guages is just an indication that something has changed.

Don't keep running them until you have done something to repair the IVR or you will burn out the movement.
 
I think I fixed the problem, the gauges were not grounded good enough. I ran a ground wire from the resister to fire wall, and gauges seem to be showing proper indications!

Thanks for the help!
 
Renegade said:
I think I fixed the problem, the gauges were not grounded good enough. I ran a ground wire from the resister to fire wall, and gauges seem to be showing proper indications!

Thanks for the help!
Click to expand...

Cool, Happy Moparing
 
Renegade said:
I think I fixed the problem, the gauges were not grounded good enough. I ran a ground wire from the resister to fire wall, and gauges seem to be showing proper indications!

Thanks for the help!
Click to expand...

I would suspect that you have not fixed the root cause of the problem.

The gauges are grounded via the sender (oil pressure sender, water temperature sender or float in the gas tank), its that variable resistance to ground provided by the sender that causes the gauge to move up and down its scale. The gauges are powered by the output of the IVR.

The IVR is powered by switched battery voltage and there is a bi-metallic strip between the voltage source and the IVR output to the gauges. When the key is switched on current flows through the bi-metallic strip to the gauges, through the gauges to the sender and to ground. Current flowing through the heating element that is wrapped around the strip causes the bi-metallic strip to heat up and the nature of the beast is it will bend. It's this motion that opens the contacts and switches off the power to the gauges. With no current flowing the bi-metallic strip cools down and the bi-metallic strip moves back closing the contacts allowing power to flow to the gauges again. This opening and closing happens very quickly resulting in an average of approximately 5 volts being feed to the gauges. A bad ground through the sender would cause the gauges to read low, its too much voltage being fed to the gauges that causes them to go full scale.

Your issue with the gauges going full scale is too much voltage which is caused by the contacts not opening in the IVR. I would venture a guess that the action of adding the ground wired (what resistor did you attach to?) disturbed the IVR enough to cause the contacts to start opening again, a rap on the top of the dash may have accomplished the same thing.

You are very likely to see this issue again. I would still plan to do one of the solid state IVR fixes in the near future.
 
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