EGT probe questions

[BigBadLou]

I have a 4 EGT (and CHT) probes on my IO-360 and a JPI "classic" (understand: "1980's") scanner. So not 700-series or 800-series monitor, nothing that fancy.
The #4 probe never read right even since I got the plane. The previous owners claim they never used the monitor (let's not go there anyway).

The old #4 probe read a dot (a dot in the 1st digit) and then usually zeros or some small value. Sign of a bad probe.
I disconnected #4 and #2 probes from the monitor harness. I swapped the probes on the harness.
Now #2 reading was bad and #4 reading was good. Thus eliminating the JPI monitor or its harness.

I bought a new probe and installed it in the exhaust pipe on #4 cylinder. Connected to the monitor and now #4 reads, again, some low value. I performed the same swap test as before and the new probe reads bad on #2 input and the #2 probe reads good on #4 input.
Installation manual for the JPI monitor says that a probe that reads low, approx 100F, is a bad probe or open circuit.

Probe measures <2.0 ohms per specs across open terminals (out of circuit).

Questions:
1) what are the chances that I got a dud out of the box?
2) does anybody have experience with Alcor M-111 EGT probes?
3) what next step would YOU take in my situation?

I will bring a small pencil butane torch with me to the hangar next time and measure the actual voltage on the good #2 probe and the new #4 probe.

Thank you in advance for any useful advice.

 

[GlennAB1]

I'd try another new one from a different vendor if you can.

 

[3393RP]

What's the signal range? Is it 0-200 mV?

 

[BigBadLou]

I'd try another new one from a different vendor if you can.

After I test it with a small butane torch, I will send it back for a replacement. Not spending another big pile of money on another one from a different vendor. I would like to get my money back if this is a dud.

What's the signal range? Is it 0-200 mV?

Normally <100mV for up to 2000F.
The spec sheet calls for approx 35mV at 1550F. Might have time to test it out tomorrow night.

 

[the_doc]

Without depressing you, is it possible you have an subtle engine issue on that #4 cylinder that is giving you a lower EGT reading compared to the other 3?

I'm no expert at all and may have misunderstood but reading your post, it suggests you eliminated the monitor and harness, and that any of the probes you tried in #4 (including a new one) are reading low still?

I bet you've done it, but could you swap say the working #2 probe and harness, onto the #4? If that reads low, that rules out prob, harness and JPI unit doesn't it?

 

[BigBadLou]

Good questions, doc. But fortunately, it is not an engine or harness issue. (lucky me)
The probe tested out bad in the end and I replaced it with another good one and all is well now.

 

[GlennAB1]

After I test it with a small butane torch, I will send it back for a replacement. Not spending another big pile of money on another one from a different vendor. I would like to get my money back if this dud.

I don't think we have much luck getting refunds on expendable parts, especially after we make them look used. How'd that go?

 

[the_doc]

Good questions, doc. But fortunately, it is not an engine or harness issue. (lucky me)
The probe tested out bad in the end and I replaced it with another good one and all is well now.

Glad it was a bad probe, great news!

 

[arnoha]

Bad out of the box seems to happen with some frequency. My plane is currently having the turn coordinator replaced again because the overhauled unit that was installed unit took 5+ minutes to erect. Fortunately, it looks like the overhaul company will eat the cost of both the unit and the labor to swap it. So, bad on them for giving me a bum unit, but good on them for covering the cost fully.

 

[BigBadLou]

Bad out of the box seems to happen with some frequency. My plane is currently having the turn coordinator replaced again because the overhauled unit that was installed unit took 5+ minutes to erect. Fortunately, it looks like the overhaul company will eat the cost of both the unit and the labor to swap it. So, bad on them for giving me a bum unit, but good on them for covering the cost fully.

I too got a bad DG when the local shop sent it for an overhaul. Unfortunately, the shop that did the replacement ate the labor costs on the replacement. The owner explained that they do so much business with the avionics shop that it evens out in the long run.
But yes, new/overhauled item mortality rate isn't 0%. It is nowhere close to 0%.
There's another thread on post-maintenance issues, do I need to link it?

 

[arnoha]

I too got a bad DG when the local shop sent it for an overhaul. Unfortunately, the shop that did the replacement ate the labor costs on the replacement. The owner explained that they do so much business with the avionics shop that it evens out in the long run.
But yes, new/overhauled item mortality rate isn't 0%. It is nowhere close to 0%.
There's another thread on post-maintenance issues, do I need to link it?

Heh, maybe.

But just to finish it my story...the replaced TC worked nicely when I flew this weekend.