Strange gauge behavior

[marc]

When I purchased it, my 84 J10 had the classic gauge problem of a burned out 12 V to 5 V converter, made the classic repair of attaching a the small solid state device and it has worked flawlessly for months. Yesterday, the oil pressure and gas failed to register anything for 10+ minutes after starting instead of their normal gradual increase. Then they registered but I think they are registering at ~75% capacity, a full gas tank shows 3/4, what had been a normal start up oil pressure of 40 psi shows up as 30? By the way, when the oil and gas were zero, the temperature gauge still registered some. Anybody ever see this before? I did make a spare voltage converter so I will pull the dash unit and look for loose connections, etc, maybe replace the circuit altogehter with the spare.
Thanks, Marc

[PossumJr]

If gauges across the board are doing the same and registering lower than they should, my first instinct is that your positive supply voltage is lower than it should be. These gauges and have a resistive element making them function so that more current means more needle deflection (more meaning towards F on the gas or 80 psi on the oil). A lower supply voltage could cause them to indicate lower so I think you are one the right path to double check your regulator and connections. If possible I would check the output on the regulator with ignition on (double check everything is grounded like it should be). Out of curiosity, how did you go about the solid state replacement, did you follow along with some of the write ups available here?

[tgreese]

Yep, low voltage seems likely. The chip is cheap, much less than a dollar. If it loses ground, it will go open, so there's no danger to the gauges.

[marc]

Yes, I used the method posted here. Like I mentioned, up until now the gauges have been consistent for months. Will check the voltage, I am aslo suspicious of loose connections.

[sirrus]

Low voltage or loose ground (more likely) would be my guess

[marc]

Intermitent failures are such a pain. Today, gauges are relatively okay and alternator out put and battery condition seem okay. I will have the multimeter in the truck to check next time the gauges act problematic.
Marc

[tgreese]

In other experience with this, seems you can test the CVR best with a test light. It's hard to see what's going on with a multimeter, since the meter display usually can't keep up with the on-off switching of the CVR. A test light will flash at the CVR switching rate, typically a little faster than once a second. You can also follow it with an oscilloscope, but most people don't own one.

The CVR is a mechanical device, turning on and off as it heats and cools. It may be hard to catch it misbehaving, if it's an intermittent problem.