How to test EGT's

[ShelbyFan88]

Anyone know how to test an EGT gauge out of the car? What do the 2 signal wires send from the sensor? Doesnt seem like it could be voltage, but I can't imagine what else it could be.

I have a gauge, used to work fine, had to replace the manifold due to strange pucks that lead to leaks, and now the gauge doesnt work anymore. Just wanted to see what I could do to test if its just the sensor thats bad, or the gauge actually crapped out.

Thanks

[D-Cal]

The typical Autometer style EGT gauge uses a type K thermocouple. There are many other types, but K is most commonly used.

A thermocouple is really nothing more than a joint between two dissimilar metals. A small electric charge is created where they meet, and one property of this charge is that it changes with temperature.

The voltage the sensor provides to the gauge is very small, measured in millivolts. That signal is amplified in the little black brainbox (Autometer uses an external amp) and used to drive the needle of the gauge.

To test the sensor, just hook an ohmmeter to see if it is still electrically connected to both ends and not broken somewhere.

If the sensor is OK and the gauge is still stone-dead, then most likely something in the amplifier box is fried. Depending on how the gauge is setup, if there is a 0-5v or 0-10v output from the amplifier to the gauge, you could try hooking up a power supply to the gauge with a couple of volts to see if it still functions and eliminate it as a problem. Make sure you know how the circuit works before doing this.

You can contact the manufacturer to see what they charge to look at it, or maybe get an electronically-inclined friend to test the circuits, they're usually just a simple amplifier with a cold-junction compensation circuit. If the amplifier is external like the Autometer system, you might be able to replace just that component. If it's built into the gauge, you might be able to trade in on a refurbished unit.

Good luck.

[ShelbyFan88]

Thanks for the tip. Its one of those old Westech gauges like the ones on thedodgegarage.com. I checked out some cold-junction compensator circuits online and I think I understand how it works now. Only problem with troubleshooting products like these is that the manufacturers never leave components labelled on their boards, so its tough to know what to replace if you can diagnose it to begin with. Anywho, I'll take a look at it when I get a chance.

[My96z]

Stick the probe in the oven and hook a 12V battery to the gauge for power. Compare what the gauge reads to what the oven is set for.

I havent tried it, seems like it would work....


Jeff

[ShelbyFan88]

i suppose i could try it, however, the westech doesnt require a battery input as far as I know. Just has two different properties of metal that are welded together and as the junction heats up, sends the signal to the gauge. Im not sure off the top of my head that my oven can get high enough to even register on the gauge...

[My96z]

I just looked at my autometer gauge and it goes down as far as 0 so maybe it will work... I will try when the wife goes to bed


Jeff