Fuel Gauge/Oil Temp Gauge

LanefourLanefour
in General Discussion
I have a 1969 PA28-140, with the 5 gauge stack on the lower panel (L Fuel, Oil Press, Oil Temp, Fuel Press, R Fuel). Recently, I have had erroneous readings in the Oil Temp and Right Fuel Gauge. They will both simultaneously rise to erroneously high readings, and sometimes they will flicker, both simultaneously. They will frequently "peg out", to the maximum readings (full tank, redline oil temp) even when I know I don't have a full tank. When I press on the gauge stack, they will both simultaneously go back to more believable readings.

It seems to me as though there may be a couple of wires crossed either in or behind the stack. Somethng is feeding extra voltage into both of these gauges, and by pressing on the stack, I must be breaking that connection. Has anyone had this problem before? Is it a matter of replacing the stack, or checking the wiring behind it for a loos connection?

Comments

  • Piper TechPiper Tech
    Check the wiring first, and if all is well than you will likely need to replace.
  • jruhnkejruhnke
    Intermittent sensor problems that affect two sensors simultaneously? Almost certainly a wiring issue. You can download the Cherokee service manual here, and depending on your serial number the wiring diagram should be either 11-54 or 11-55. The wiring for the two gauges you mentioned is very similar between those two drawings.

    Had you said that the gauges go off-scale low, I'd say check the 12V source voltage either leaving the left fuel gauge or coming into the oil temp gauge.

    Unfortunately, you said they jump off-scale high, which should only happen if the other terminal is shorted to ground (instead of going through the resistive sensor in the fuel tank or oil system). It's hard to imagine how two terminals a couple of inches apart from each other are both getting shorted to ground simultaneously. Still, that's the indication you're reporting, so the troubleshooting should be to try to see what's going on with those terminals.

    I don't know what your '69 is like, but with my '73 it's hard to get eyeballs on those connectors. I was able to lie on my back with my head underneath the panel and use a a flashlight and an inspection mirror to diagnose a loose oil temp gauge wire once, but it was no fun.
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