EV2 pyrometer problem

[CassMori]

I've just installed an ISSPRO EV2 pyrometer & trans temp gauges (new, from US Diesel Parts), and am having an issue with the pyrometer.

The gauge reads 0 all the time, unless the thermocouple is removed from the fitting in the manifold. When I do this, and just let it hang in open air, the gauge shows ~80-90 degrees (current ambient temps here). When the thermocouple is replaced in its fitting (or even just touched to it), the gauge will either peg out, or bottom out.

Originally, I had the third (copper/ground) wire in the harness connected to the gauge (as per the included instructions). It was suggest to me that this could be causing the problem (having an extra ground connected), so I disconnected it from the gauge - which made no difference.

Is this a problem with the thermocouple? Or with the gauge/wiring?

Thanks for any help.

[MichaelP]

This is an unusual set of symptoms. The shield wire for the thermocouple (pin #6) is not necessary in most applications, but also should not cause any issues. It is just necessary to meet the high standards for electromagnetic immunity in SAE testing.

Could you please double-check the wires to the gauge? Starting from the driver's side, when the gauge is in its normal orientation, pin #1 should be red (ignition), #2 orange (dimmer), #3 black (ground), #4 yellow (thermocouple +), #5 red (thermocouple -), #6 bare copper (shield). Please note that there are two red wires, the one from the truck ignition should be in pin #1, the thermocouple one should be in #5.

Please let me know what you find, and we'll proceed to the next step.

Regards,
Michael Pliska

[CassMori]

Thanks for the reply, MichaelP, I will double check the wiring connections again at first opportunity.
One thing I meant to mention, don't know if it has any bearing or not, but I have the pyrometer ign., dimmer, and ground piggy-backed with my trans temp gauge (which is working normally). The trans temp is first, pyrometer last.

[MichaelP]

Piggy-backing (daisy-chaining) the wires should not have any effect, they were designed to be used that way.

[CassMori]

I've double checked the wiring, and it is correct.

Would anti-sieze on the fitting in the manifold affect the thermocouple? The directions said to add some to the exposed threads, but I wasn't sure if it meant the end that screws into the manifold, or the end used to tighten the thermocouple. I applied it to both, but when I had problems, my first thought was that it was causing an issue, and removed all of the anti-sieze, but it did not seem to make any difference.

[MichaelP]

The anti-seize is for the threads into the manifold, but it would not hurt the other location. Do you have a decent multi-meter (with a milivolt setting) handy? If so, please measure the voltage between the yellow and red thermocouple wires (meter +probe to yellow, - probe to red), both with the engine off and with the engine idling. This should tell us if the problem is with the thermocouple or the gauge head.

Thanks,
Michael Pliska

[CassMori]

Thanks for the help - I'm not sure if my meter will do millivolts, but if it won't I'll locate one that will and check the voltage tomorrow as soon as I can. How much voltage should I see?

[CassMori]

I've just checked the thermocouple - at "cold" it read 1.0 on a 200mv scale. After starting, it read 3.7, then moved to 3.8, and seemed to stay there. After turning the engine off, it had dropped to ~2.6, then gradually fell off to 1.8 (when I stopped monitoring it).

[MichaelP]

I assume it was threaded into the exhaust when you measured these numbers? What was the ambient temperature? If it was hot out, then these numbers seem about normal or very slightly low. I'm guessing there may be an internal short in the gauge, please PM me your mailing address, the part number on the gauge, and where you bought it originally, and I'll have a replacement shipped.

Regards,
Michael Pliska

[CassMori]

Michael,

Thanks for the help, I've just sent you a PM with the requested information

Neal