Chaotic Pryometer

1718 Views 9 Replies 3 Participants Last post by danjreed, Jul 18, 2007

maccwall

Discussion Starter · Jun 14, 2007

My Steward Warner pyrometer that I have had in my truck forever (at least 5 years) does not seem to functioning properly recently. I do not know if it's the gauge itself or the thermocouple which is a K type or maybe my EGT's have just cooled off. I have taken some Ohm load readings of the gauge and the contacts from the thermocouple but I do not know what these readings mean other than the fact that they are reading something. I have bought another gauge, a Hewitt Industries gauge, but have not hooked it up. The Ohm readings on that gauge differ though from the Steward Warner gauge. Can anybody help me out here. Leads at the end of my thermocoupler read 8.4 Ohms (that's at idle), SW gauge reads 66.2 Ohms Hewitt gauge reads 54.6 Ohms.
Thanks in advance

Peace,
Todd

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danjreed

· #2 · Jun 15, 2007

You're using the wrong measurement for the thermocouple. You should be using Volts.
Thermocouples use a bimetallic junction to create a small voltage between the two leads. This voltage is proportional to the temperature at the junction.
The EGT gauge is basically a voltmeter calibrated to read in degrees, so measuring resistance across it is meaningless. Hopefully the gauge has a high impedence amplifier, otherwise you might have damaged something.

Can you give us some EGT (gauge, not voltmeter) numbers before and after?

Daniel

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danjreed

· #4 · Jun 15, 2007

I do remember reading somewhere about a pyro gauge going nuts occassionally. I don't remember what was causing the interference, but moving the wires fixed it.
Have you checked the pre-turbo exhaust system for leaks? I.E. manifolds at the block, up pipes, collector doughnuts, etc... I seem to remember during one of my conversations with Dale Isley that he mentioned blowing a doughnut on the interstate (up hill, w/ trailer, playing with dodge/cummins), and he lost several pounds of boost along with EGTs going down about 300deg. Has your boost changed any?

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danjreed

· #7 · Jul 7, 2007

It's entirely possible that the gauge is out of calibration. I'd expect that to show gradually, not like what you're describing.
After 5 years, it might be time to replace the probe. Maybe it's not quite what it used to be?
If you can, check the temp w/ a laser gun. Or just add 300deg in your head and run with that.
I'm out of ideas.

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danjreed

· #10 · Jul 18, 2007

Good.

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