Gauge issues?

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Madhatter1776

Madhatter1776

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ok, I have a 75 duster, I have been having an issue with my temp and fuel gauge's. I did fry my old fuel gauge testing it. I had to replace the fuel sending unit when I cleaned out the fuel tank. I also bought some used gauges and replaced that voltage regulator when I swapped out gauges. For about two week after my temp worked ok, however my fuel gauge was never accurate. I did some testing to see if the wire had a bad ground, I did find that the voltage out of the main harness was wacky. Then one day I shut off the car, and the next day, everything was back the way it was before I fried the fuel gauge. I think the circuit board might be bad, however I am wondering if there is something I should check first. I f it the circuit board I am switching to all aftermarket mechanical gauges, if its something simple I wont. any help would be appreciated.

Thanks
 
New pc boards aren't that expensive. When you had your dash out and replaced the gauges did you notice any loose pins on the back of your pd boards ?
 
If you have "wacky" voltage like you discovered I would say tackle that first even if you put aftermarket gauges in it they will still be getting "wacky voltage"
 
I did not notice any pins loose on the board, however I was not looking to hard as I thought that the Voltage regulator was going to solve the problem, I do think it is a ground issue, but not sure as to where to start to look, which is why I was thinking about mechanical gauges.
 
I've typed this about a thousand times

STOP thinking of the gauges as 'parts' and START thinking of it as an "end to end system."

Picture in your mind how the long path of the circuit is laid out

FIRST the cluster MUST receive "good" solid battery voltage.

This means the vehicle's harness, bulkhead connector, ignition switch and connector, EVERYTHING "before" the gauges and clusters must be up to par.

Voltage comes to the cluster connector / PC board pins. Don't "assume" they are OK, actually check or repair them. CLEAN them, resolder them. CHECK that you have good battery voltage at that point. I don't mean a test lamp, I mean actually and critically measure it with a meter. Should be nearly EXACTLY the same as battery voltage.

The IVR. Replace it with a modern solid state one, such as RTE

The IVR SOCKET. The IVR fits into springy brass fingers crimped into the board, BUT those fingers may NOT be making good contact with the board traces. Solder jumpers across.

The gauges. The gauge studs may not be making good contact with the board, loosen tighten the stud nuts several times to scrub the board clean, and / or replace the nuts

the gauges themselves. Might be out of calibration. You can easily check them, AFTER repairing other issues, and before installing in the car, by using resistors to substitute for the senders.

The senders. These individually leave the gauge studs, go back out through the board connector pins, and in the case of oil (if equipped) and temp, go through the bulkhead connector, ALWAYS a suspect. Last, suspect or at least check the sender connector

Fuel.......same deal.......goes through the kick panel connector on the way to the rear, and that connector could be a problem, although probably rare. And the connector at the tank can be suspect.

Of course the senders themselves, or bad sender grounds.........which is why, once again, you test it AT the sender connectors with your substitute resistors.

Test resistors. You don't need to build this. You just need at minimum, a mid scale test resistor, and if you can, resistors for full scale and the bottom of the scale. That means 73--75 for MT/ cold, 23--25 for mid scale, and 10-15 for full scale.

For example, for mid scale, go to Radio Shack and buy 1 package of four 100 ohm, 1/2 watt resistors. Wire all four in parallel which gives you 25 ohms. When hooked in place of a sender this should give you 1/2 (mid) scale on the gauge under test

http://www.forabodiesonly.com/mopar/showthread.php?t=179517
 
Just purchased a 1967 notchback. I was surprised that all the guages except the gas guage were working. If I remove the wire from the sending unit and ground it to the frame, the gas guage goes to full. Does this mean the sending unit is bad or could it be a bad tank ground, and if a bad tank ground where is that located?

Thanks
 
The ground for the sender is a little metal strap snapped on the fuel line over the rubber hose there. There is a pic of that jumper in several similar threads. It could be missing or rusted enough to prevent continuity.
If you prove that sender ground is good the sender is definitely the fault. If the senders float was filled with fuel the gauge needle would at least climb from its home position to the empty mark at switch on.
Hope this helps and next time start your own thread rather than hijack someone elses.
 
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