Cherokee 140 CHT/EGT probes

ircphoenix

ircphoenix

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ircphoenix
Pretty sure my mechanic broke the probes when they removed/reinstalled the plugs in my engine. I get zero movement from my needs in the cockpit. They used to move. Now they don't. Is it possible that both probes got crushed somehow? Or is it more likely that it's some kind of dumb wiring thing?
 
Likely some dumb wiring thing. The probes usually aren't damaged unless removed and even then it's fairly rare.
 
Hope so. I know there was some panel work when they installed my new strobes... so hoping they forgot to reconnect something in there without costing me another AMU.
 
ircphoenix said:
Pretty sure my mechanic broke the probes when they removed/reinstalled the plugs in my engine. I get zero movement from my needs in the cockpit. They used to move. Now they don't. Is it possible that both probes got crushed somehow? Or is it more likely that it's some kind of dumb wiring thing?
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The EGT probe doesn't come out when plugs are removed; if it is the original Piper device there should be a single probe in the exhaust pipe of one of the rear cylinders. Unless the CHT probe is one of those spark plug gasket replacement types (instead of threaded into the head of one of the cylinders) it too shouldn't have to be disturbed during spark plug maintenance. Sounds more like a wiring issue?
 
All I know is that they worked during my prebuy and they stopped working after the annual when 3/4 of the top was rebuilt. I looked inside forward of the firewall and I didn't see anything that jumped out at me. And inside behind the panel I wouldn't even know where to begin since all that stuff is voodoo to me.
 
ircphoenix said:
All I know is that they worked during my prebuy and they stopped working after the annual when 3/4 of the top was rebuilt. I looked inside forward of the firewall and I didn't see anything that jumped out at me. And inside behind the panel I wouldn't even know where to begin since all that stuff is voodoo to me.
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When you say "3/4 of the top was rebuilt" do you mean you had cylinders removed and changed on the engine during the annual? That type of work usually means the probes have to be removed as the exhaust stacks are disconnected and the CHT has to be reinstalled in the new cylinder head - quite a different matter from spark plug maintenance only.
 
GRG55 said:
When you say "3/4 of the top was rebuilt" do you mean you had cylinders removed and changed on the engine during the annual? That type of work usually means the probes have to be removed as the exhaust stacks are disconnected and the CHT has to be reinstalled in the new cylinder head - quite a different matter from spark plug maintenance only.
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Yup. Three cylinders were replaced. Now I'm skeered. I'm a pilot on a budget dammit.
 
You don't mention how much time is on the engine after the top overhaul but if I were you (assuming break in is not compete) I'd get this sorted before flying too much more. I've seen a lot of people fry cylinders due to lack of awareness of what the temps were doing as an IA. I fried a set myself once!

Also, taking the top cowl off of your Cherokee is a 15 second job. Grab a flashlight and take a look. Exhaust stacks for the egt and either a spark plug gasket type cht or probes threaded into the bottom of the cylinders.


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So official diagnosis.... the CHT/EGT is officially dead and needs to be replaced. The probe was destroyed, the harness was chopped off.

Anyone got a recommendation. Figure I'm going to be declaring bankruptcy here in a minute or two, might as well replace stuff willy nilly.
 
ircphoenix said:
So official diagnosis.... the CHT/EGT is officially dead and needs to be replaced. The probe was destroyed, the harness was chopped off.

Anyone got a recommendation. Figure I'm going to be declaring bankruptcy here in a minute or two, might as well replace stuff willy nilly.
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This doesn't sound right.
If the gauge is "dead" then why were the probes destroyed and the harness chopped off? A dead gauge would suggest that is all that needed replacing and the probes and wiring were fine? Usually the EGT probe will fail before anything else, because it is stuck into the corrosive exhaust gas stream - but replacing an EGT probe is not difficult or all that expensive; but that presumes the gauge was working fine.

If this is the original Piper gauge (and not an aftermarket Alcor or something like that) I would look for a used replacement from a salvage - that will be your lowest cost alternative I would think. Check both eBay and the used aircraft salvage outfits.
 
Since you are going for "broke", why not install an engine monitor? I replaced my EGT with an Insight, although if I had to do it over, I would probably go EI.
 
ircphoenix said:
So official diagnosis.... the CHT/EGT is officially dead and needs to be replaced. The probe was destroyed, the harness was chopped off.

Anyone got a recommendation. Figure I'm going to be declaring bankruptcy here in a minute or two, might as well replace stuff willy nilly.
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If they busted it up and chopped the harness, why are you paying for it?

There are some good deals on used JPIs on barnstormers and eBay.



Boomer said:
...) I'd get this sorted before flying too much more. I've seen a lot of people fry cylinders due to lack of awareness of what the temps were doing as an IA. I fried a set myself once!...
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Dude, plenty of folks fly planes everyday without multi cylinder monitors, most of the planes I learned to fly in didn't have a monitor or even a single point and they weren't exactly running through jugs.
 
GRG55 said:
This doesn't sound right.
If the gauge is "dead" then why were the probes destroyed and the harness chopped off? A dead gauge would suggest that is all that needed replacing and the probes and wiring were fine? Usually the EGT probe will fail before anything else, because it is stuck into the corrosive exhaust gas stream - but replacing an EGT probe is not difficult or all that expensive; but that presumes the gauge was working fine.

If this is the original Piper gauge (and not an aftermarket Alcor or something like that) I would look for a used replacement from a salvage - that will be your lowest cost alternative I would think. Check both eBay and the used aircraft salvage outfits.
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The mechanic said he couldn't find a make on the gauge itself. I'm actually thinking it is an original Piper gauge but wtf do I know.

And if it is just a matter of replacing the probes, do ANY probes work with the original Piper gauge?
 
James331 said:
If they busted it up and chopped the harness, why are you paying for it?

There are some good deals on used JPIs on barnstormers and eBay.





Dude, plenty of folks fly planes everyday without multi cylinder monitors, most of the planes I learned to fly in didn't have a monitor or even a single point and they weren't exactly running through jugs.
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Because there's a zero percent chance I'm taking it back to the shop that charged me 15 grand on an annual.
 
ircphoenix said:
Because there's a zero percent chance I'm taking it back to the shop that charged me 15 grand on an annual.
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Holy hell...can almost buy a Cirrus for that much...jk
 
ircphoenix said:
Because there's a zero percent chance I'm taking it back to the shop that charged me 15 grand on an annual.
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Don't bring them the plane, just bring them a bill. You break it you buy it.
 
Here's the text message I got from the A&P.

"As for the CHT, there seem to be two issues with the unit. The first one is the washer style probe is no good anymore, it was barely hanging on. The other problem, I noticed that one wire from the CHT probe was cut off behind the instrument panel. Here is what the CHT/EGT instrument looks like from behind. It also looks like the CHT probe and harness has been replaced before, because it looks fairly newer than the EGT harness. I couldn't get a name from the instrument. You might want to shop around for a new EGT/CHT system or if you like I can get you a quote."

ccb412ee26bf516d74f3aae367549818.jpg
 
ircphoenix said:
The mechanic said he couldn't find a make on the gauge itself. I'm actually thinking it is an original Piper gauge but wtf do I know.

And if it is just a matter of replacing the probes, do ANY probes work with the original Piper gauge?
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Probes don't often work between different brands (e.g. an EI probe won't work with a JPI instrument), but a lot of the older stuff (Alcor, Piper) might be more interchangable. It sounds like your system was toasted during the annual? Take a photo of the front of the gauge and post it here. There's so many people here that have a real depth of knowledge that someone might be able to identify it, and that might help determine if it's worthwhile spending any time or money to try to find new probes and salvage it by fixing the wiring, or if the cost of that is likely more expensive than just replacing it.

imo the EGT is the more important of the indicators. I never had CHT measurement in any of my Piper singles, just EGT, so if you have to replace you might save some money limiting to EGT only.
 
GRG55 said:
Probes don't often work between different brands (e.g. an EI probe won't work with a JPI instrument), but a lot of the older stuff (Alcor, Piper) might be more interchangable. It sounds like your system was toasted during the annual? Take a photo of the front of the gauge and post it here. There's so many people here that have a real depth of knowledge that someone might be able to identify it, and that might help determine if it's worthwhile spending any time or money to try to find new probes and salvage it by fixing the wiring, or if the cost of that is likely more expensive than just replacing it.

imo the EGT is the more important of the indicators. I never had CHT measurement in any of my Piper singles, just EGT, so if you have to replace you might save some money limiting to EGT only.
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Part number on the back makes it look like an original Piper part.

sIGmvfqbT15z88ZvUyUf_XEaOoYmdfBrb6jBdbfRhZANY3k99O7uMeQxjlK1UxQ-yPvLwrEnWPd6A2KTANAwQexXL94EZtR9FqeLyBKR2rmkPtPxXpwuzpTxTIWJwLoXFbpXqlkWRJk8BoQ7ze2LJqW70TccMooYq-wj9YJ7rhDf4bd93Eu-4xL9_O-U14uUJWWsfzbpAIooqwRsoH9KAqR5Pw606XhjPUJJS5U-TQqYg-Km1vafnWjNFG1R_1wdgfYKK-JF1EVe6AqosV0j0li43iEdgAYYTCoL_1VSWGmLwJCi1KUl49ugKLD16dZqNeyCLYP6zfPEs6W-bacdwIDa--xQUQQODoTk5fYKJp0uZs9HwHpiLlWqui9ZqCpj5FuimYbOMtYPZ6UC_NnRWtSQrB8ibbVk3sUtqrTvHKQbhJPO_m5y44UL3fDEbyb9rM3fmxYWCAsRxaB5D7vpGOm8AOb-55F-seLqmquCoZhfiClwydHTDvmMY8CTBvOZbmW4MA_Hp931UZovBtniqFn77nWd0cFOwn61mq6lz1EHObKhqtSs4kPhU2k2UESK5xg8hMD6KjX6jqagH4pS_lNn8KEEaR4CH5KQHdli8QuOS54_=w1707-h960-no
 
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