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  #1  
Old 11-07-2017, 07:35 AM
jbell2355 jbell2355 is offline
 
Join Date: Sep 2017
Location: Marquette, MI
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Default GRT EIS/EGT Problem - need help with diagnosis

Hello everyone! This is my first post; I've been lurking for a some time as I was shopping for my RV7-A (which I purchased last month). This community is amazing and I hope that some day I'll have something to contribute - other than $.

Anyhow, on to the problem...

Immediately following the pre-buy inspection, I flew the ferry pilot back to his home base in my new plane, N811AK. On the return flight, cylinder #4 EGTs were occasionally exceeding the limits and reading about 200 degrees hotter than the other 3 cylinders. The temp on #4 fluctuated right along with the other 3 cylinders, but was always hotter. I figured the problem was bad probe, and continued flying 20 hours until my first oil change.

I brought the plane back to my mechanic (same buy who did the pre-buy) for the oil change. When we uncowled the plane, I almost fainted when I saw the upper spark plug lead for #4 laying on the cylinder, unplugged. The mechanic failed to replace the lead when doing the inspection! We figured this explained the high EGTs: unburnt fuel was combusting in the exhaust causing high temps. We pulled the plug, blasted the lead off and replaced the plug. I flew home after the oil change expecting normal EGTs but #4 was still reading hot.

Next, I swapped the #2 and #4 EGT probe and found that this resulted in the high EGT reading moving over to cylinder #2, indicating a bad probe. I ordered and installed a new probe, but am getting the same high readings with the new probe. It would seem the problem is somewhere between the EGT probe and the EIS.

So, the question is...what's the problem, how do I confirm it, and how do I fix it? Your thoughts are very much appreciated.

Jesse
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  #2  
Old 11-07-2017, 08:25 AM
tim2542 tim2542 is offline
 
Join Date: Aug 2009
Location: Redding,Ca
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There is no normal or red line temp on exhaust temps and you should not expect all 4 cylinders to run the same egt. Of course there is what’s normal for your plane. All we care about is relative to wherever egt peaks and hopefully all 4 peaking at the same fuel flow.
Having said that it does sound like there is a 200 degree error from your experiments. I would see if the new probe reads the same on another channel. If it does the probe is out of calibration some. If it does not read the same there a problem in the EIS or wiring, almost certainly at the connectors. Use some standard to test the probes, like boiling water or hot oil, as again the cylinders will not be the same due to installation differences so flight testing will not tell you what you need to know.
While your there you might test the CHT probes also using boiling water.
Tim Andres
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  #3  
Old 11-07-2017, 10:58 AM
jbell2355 jbell2355 is offline
 
Join Date: Sep 2017
Location: Marquette, MI
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Thanks Tim. Based on your feedback and an e-mail exchange with GRT, my next step will be to install new female terminals where the probe connects to the harness. I'm hoping that'll do the trick.

Based on reports from the builder, these EGTs are not normal for the plane. The high EGT persisted after swapping out the old probe for new, so the probe isn't the problem either.
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  #4  
Old 11-09-2017, 08:28 AM
jbell2355 jbell2355 is offline
 
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Location: Marquette, MI
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I crimped on new terminals, but I'm still getting high EGT readings on #4. Next step is checking the wires going into the connector on the back of the EIS. If that isn't the problem, I'm out of tricks.
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  #5  
Old 11-09-2017, 08:52 AM
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erich weaver erich weaver is offline
 
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The EGT wires are special thermocouple wire. If it was ever replaced with standard wire, that might be the problem.

Erich
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  #6  
Old 11-09-2017, 11:33 AM
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skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 560
Default EGT Circuit Troubleshooting

Quote:
Originally Posted by jbell2355 View Post
I crimped on new terminals, but I'm still getting high EGT readings on #4. Next step is checking the wires going into the connector on the back of the EIS. If that isn't the problem, I'm out of tricks.
You might try swapping the #4 EGT probe channel contacts at the EIS connector with cylinder #2 and re-testing. This should help further narrow down the problem to either aircraft wiring or the EIS unit itself.

Skylor
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