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Do I have a bad EGT sensor?

bill.hutchison

Well Known Member
Whilst futzing about the Shenandoah Valley today, I noticed that I had an EGT reading abnormally low compared to the others. I have a GRT EIS 4000. It's a simple design but I gotta admit I'm in love with the thing.


Won't lie - I'm a better pilot than I am systems guy and I am still learning this airplane. I don't recall seeing something like this before, but I might also be a moron and I'm totally mis-interpreting what I'm seeing.

The first picture shows my EGTs as I was be-bopping along:
https://photos.app.goo.gl/U1cqzricz7o6959P8


The second picture shows the CHTs:
https://photos.app.goo.gl/Ty4UVC6txNqb3R3V8


The engine was performing just fine - no issues, everything was smooth. And since the CHTs were where I expected them to be, I'm wondering if the odd-man-out in the EGT picture is a bad sensor?

If so, I'm guessing troubleshooting would involve moving/swapping the sensor with another one and then seeing if the problem followed the sensor or remained in the same place.

If it follows the sensor, then the sensor is bad. If it doesn't.....

what do I do?

(still trying to figure out how to embed the images. following directions but every time I use the Insert Image it hides the link)
 
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Can you swap the sensors without too much trouble? I'd try that first given your reported "smooth engine" run and the rather normal CHT's.

-Marc
 
(still trying to figure out how to embed the images. following directions but every time I use the Insert Image it hides the link)

Easiest if pic is stored on same device you are using. If it is , click on the paper clip icon next to the smiley face in your reply. New screen opens, you go locate/ choose file then click upload, then close this window button... preview. Good luck
 

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Whilst futzing about the Shenandoah Valley today, I noticed that I had an EGT reading abnormally low compared to the others. I have a GRT EIS 4000. It's a simple design but I gotta admit I'm in love with the thing.


Won't lie - I'm a better pilot than I am systems guy and I am still learning this airplane. I don't recall seeing something like this before, but I might also be a moron and I'm totally mis-interpreting what I'm seeing.

The first picture shows my EGTs as I was be-bopping along:
https://photos.app.goo.gl/U1cqzricz7o6959P8


The second picture shows the CHTs:
https://photos.app.goo.gl/Ty4UVC6txNqb3R3V8


The engine was performing just fine - no issues, everything was smooth. And since the CHTs were where I expected them to be, I'm wondering if the odd-man-out in the EGT picture is a bad sensor?

If so, I'm guessing troubleshooting would involve moving/swapping the sensor with another one and then seeing if the problem followed the sensor or remained in the same place.

If it follows the sensor, then the sensor is bad. If it doesn't.....

what do I do?

(still trying to figure out how to embed the images. following directions but every time I use the Insert Image it hides the link)


Since the CHT's are pretty much in line with normal operations, the EGT thermocouple is bad, or there is a high resistance somewhere in the line to the EFIS. Check the tightness of the connection out in the engine compartment for looseness, or corrosion. Next step is to swap leads and see it that switches the low reading to the other cylinder. If so, then it's probably a bad probe.
 
I've replaced the probe on mine twice, previous owner twice. Send the unit to GRT and was told it was not the unit. Pretty much gave up on it. only thing left is to replace wire running through fire wall and dsub connections to unit.

Jon
 
Me too

Hi Bill, I have exactly the same problem on my 9A. O-360, same position. My A&P replaced the sensor but didn't solve the problem. Engine runs great and all other indications normal. I haven't sent my unit back to GRT.
 
I've seen this twice. Both times it was the sensor. I would take the sensor out of the exhaust pipe and look at it.
 
EGT sensors fail. It's a fact of life. Keep at least one in your stock of maintenance spares.

At one time, GRT was selling regular and long life probes. Now only one kind (the long life). I had what I will call infant mortality on 2 regular probes at around 200 hrs. The third went about 6 months ago after around 850 hrs. In all cases the sheath in the exhaust flow was eroded to expose the tc junction wires and damage them. From a fluid dynamics point of view it is interesting that the erosion is mostly on the downstream stagnation point at the back of the cylindrical probe.

I would not bother removng the old probe from the exhaust until you have one in hand to replace it.
 
EGT sensors fail. It's a fact of life. Keep at least one in your stock of maintenance spares.

At one time, GRT was selling regular and long life probes. Now only one kind (the long life). I had what I will call infant mortality on 2 regular probes at around 200 hrs. The third went about 6 months ago after around 850 hrs. In all cases the sheath in the exhaust flow was eroded to expose the tc junction wires and damage them. From a fluid dynamics point of view it is interesting that the erosion is mostly on the downstream stagnation point at the back of the cylindrical probe.

I would not bother removng the old probe from the exhaust until you have one in hand to replace it.

Yeah, this seems to be the consensus. As I am prepping for a couple of minor Mx projects right now, this will just get added to the list while I've got the cowl off the airplane.

I do have a spare probe that the previous owner included - I can't remember if it's a CHT probe or an EGT probe, but it seems like having a spare or two of each is a good idea so I'll go ahead and order I think.
 
EGT probe

Bill,

Have you pulled off the engine cowls and looked at the affected egt probe? I had the exact same symptoms and discovered the egt probe clamp that goes around the exhaust had broken clean through. The probe was still barely in the exhaust but flopping around. Replaced the probe with a new one and problem solved.
 
Bill,

Have you pulled off the engine cowls and looked at the affected egt probe? I had the exact same symptoms and discovered the egt probe clamp that goes around the exhaust had broken clean through. The probe was still barely in the exhaust but flopping around. Replaced the probe with a new one and problem solved.

I have looked at the probes, and one of them does sort of look as if it had pulled partially apart but I don't know if it's the potential bad one or not. It's where I'm going to start, though.

The issue - and this is annoying to admit - is that I don't know which probe corresponds to which EGT value on the EIS4000 - is it #1? #4? - because I haven't traced the wiring yet to see which one it is. And this relationship isn't documented in the builder's paperwork, although he seemed to be pretty good about most other stuff.

My plan right now is to hook up some power, then shine a heat gun on each one so I can figure out which one in the display corresponds to which cylinder, and then that will let me zero in on which probe may be broken. Just haven't had a chance to get to it yet. Hoping to handle that on Saturday.
 
EIS

Indicates #4. The 4000 panel reads left to right 1-2....next line 3-4. Like you said, power up eis4000, put heat on #4 and see if it moves. Only if wrong pin in wrong place in connector would it read anything different

1 - 2
3 - 4

Cheers
 
Ohmmeter test?

You can run the resistance test per the instructions listed in the EIS Troubleshooting Guide (version 09/17/15) page 18.
 
Half a victory!

A couple of people have asked me about this so I thought I'd post an update....

I turned on the EIS and put a heat gun on it, got it nice and toasty, and verified that the temperature wasn't moving on it. Moved the heat gun to #2 and made sure it was working - it was - so that was a good test.

I removed the old EGT sensor and installed a new one. Did the heat gun test again and BEHOLD the temperature was coming up under heat! Yay! Heat up the shrink tubing and all good. (That's the half victory)

Pulled the plane out of the hangar to run up the engine (I'm also chasing some leaks - that will be another thread) and noticed the issue remains. While the other three EGT sensors are getting into the 750-800-900 degree range, the #4 is still just showing a just a couple hundred degrees. Not right at all.

The sensor is brand-new, so that makes me think that either the sensor is bad or there is a wiring problem between the quick-connects and the EIS. So the next step is to swap the sensor with a known good and see if the problem follows the sensor or stays on #4.

I did take a look at the EIS troubleshooting guide, and it still turns out to be somewhere in that wiring I'll try that - but I'm not too smart with a voltmeter (skill #4,521 that I have to learn) and getting to the connector behind the EIS in the panel is a real pain; there aren't service loops in there so I gotta get it from behind the panel.

BUT - I did a maintenance task without assistance today, and for me that was a big victory. So even though I didn't succeed I'm on the road to it and I feel pretty good about that.

Now I gotta chase these stupid oil leaks....
 
Rather than swap the probes to check, could you swap the wires? Either will achieve the same end.
 
Rather than swap the probes to check, could you swap the wires? Either will achieve the same end.

Yes. Did this today. Problem did not follow the sensor, which tells me it is somewhere in the wiring between the sensor connection and the EIS.

The troubleshooting manuals don't really address this specific scenario so a support call to GRT might be in order.
 
SOLVED

GRT suggested that I re-terminate the spades of the quick connects on the EIS side. They looked pretty good to me but I did this anyway.

Whilst doing some other stuff under the panel, a guy helping me out pulled the backshell of the connector going into the EIS. He noted that pins 7 and 19 had backed out, which happened to be the pins for EGT #4.

So he re-seated them. We reconnected everything, fired up the motor and it's now working correctly.
 
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