Pyrometer Gremlin

861 Views 7 Replies 3 Participants Last post by old man dave, Jan 11, 2015

OBSBEN

Discussion Starter · Jan 6, 2015

I inherited the gauges in the truck when I purchased it. Both the Boost and Pyrometer are AutoMeter brand. The wiring is OK, not necessarily something I would deem "Professional", but it functions none the less. The Boost gauge functions properly and reads correctly. The Pyrometer, on the other hand, does not. I have checked, and re checked everything to ensure a proper install. It is all in place. The pervious owner claims it functioned fine beforehand, but thats just a "He said, She said" at this point. I have read where the length of the probe wiring is critical to acurate readings. With that, I am unsure if the probe wiring has been done correctly. The wire coming directly from the probe is quite long, but coiled up on the chassis and linked into a seperate wire that runs through the firewall. Is that normal? I have also contacted Autometer to ensure the proper wiring of the gauge itself...so thats good. One more item would be the probe itself. I know it needs to be a certain length inside of the pipe.....I have no idea what that is. Also, how do I test signal from the probe to ensure it is even working? Any help is appreciated!!!!!!

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Bradbilt

· #2 · Jan 6, 2015

OBSBEN said:
I inherited the gauges in the truck when I purchased it. Both the Boost and Pyrometer are AutoMeter brand. The wiring is OK, not necessarily something I would deem "Professional", but it functions none the less. The Boost gauge functions properly and reads correctly. The Pyrometer, on the other hand, does not. I have checked, and re checked everything to ensure a proper install. It is all in place. The pervious owner claims it functioned fine beforehand, but thats just a "He said, She said" at this point. I have read where the length of the probe wiring is critical to acurate readings. With that, I am unsure if the probe wiring has been done correctly. The wire coming directly from the probe is quite long, but coiled up on the chassis and linked into a seperate wire that runs through the firewall. Is that normal? I have also contacted Autometer to ensure the proper wiring of the gauge itself...so thats good. One more item would be the probe itself. I know it needs to be a certain length inside of the pipe.....I have no idea what that is. Also, how do I test signal from the probe to ensure it is even working? Any help is appreciated!!!!!!

Typical Autometer EGT wiring has a short lead wrapped in a "stainless" insulation coming off the probe. It then BOLTS to the longer yellow lead that is hardwired from the gauge with heat shrink on arch bolt to insulate them from each other.

YES there is typically too much wire so you coil it up and zip tie out out of the way

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OBSBEN

Discussion Starter · #3 · Jan 6, 2015

Thanks, Bradbilt! That is the way it is installed. GRRRR!! LOL! Mabye a fault in the probe? Do you happen to know of a way to check that?

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Bradbilt

· #4 · Jan 6, 2015

OBSBEN said:
Thanks, Bradbilt! That is the way it is installed. GRRRR!! LOL! Mabye a fault in the probe? Do you happen to know of a way to check that?

Swap it with another is the only way i know

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OBSBEN

Discussion Starter · #5 · Jan 6, 2015

I'll see what I can figure out! Thanks for the input!!!

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old man dave

· #6 · Jan 6, 2015

Thermocouple lead length within reason does not make a difference in accuracy. I've worked with thermocouple systems with leads approaching 100' without accuracy problems providing the leads were connected properly. Pusher diesel buses are an example where the lead length is about 50-60'.

Check all of the connections, wear spots in the insulation and try a different thermocouple if possible. Also check if the same lead color is connected to the same color at the connections (the red and yellow) and at the meter since the thermocouple leads are different metals and can throw off the readings if swapped.

Disconnect and short the leads at the thermocouple end and check continuity at the meter end. That will tell you if the leads are broken.

If you have an adjustable depth pyro probe,, then set the depth so the tip is at the center of the exhaust pipe.

You need a millivolt potentiometer to check output voltage (millivolts) of the probe, something not normally availiable. Its just as easy to sub in a different probe.

I don't know if the AutoMeter pyros need power or not. Some pyros do and some don't. If it has an amplifer then the amplfier needs to have +12 volts and a ground in addition to the thermocouple and meter leads. Some Isspro meters have the amplifiers.

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OBSBEN

Discussion Starter · #7 · Jan 8, 2015

Wow! Great info!! I have some work to do now! Thank you! I'll re post with what I find.

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old man dave

· #8 · Jan 11, 2015

The yellow wire is the positive connection and the red wire is the negative connection, also. The lead hookups are polarity sensitive.

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