EGT probe connections

[vlittle]

Yesterday, I had several of my EGT probes start to misbehave in flight.  I've determined that the fast-on connections are the problem, so I reseated them and coated them in Corrision-X and will fly again.

They all started to misbehave at once.  On the ground, here's what I got.  First, the odd cylinders were bad.  After a power cycle on the SV, I checked again and the even cylinders were bad.

I'm almost convinced that the connections are the root cause, but this is pretty odd behaviour.  Is there something about the EMS input structure or system grounding that could be at issue here?   

And yes, I see the CHT is wrong in the first screen shot... same root cause?

Vern

 

[jakej]

Vern
You are correct re the connections as they are the cause of most symptoms - if you do a search on this topic you'll see my posts & my suggested causes/solutions

Pm me if you want & I'll call you to discuss this

Jake J

 

[vlittle]

I've replaced all of the fast on terminals with butt connectors now.

I had a good look at the terminals provided with the probes and discovered that they are all crimped incorrectly. They are all single-crimped and the insulation is crimped with the wire, thus preventing a good gas-tight seal.

I could have just replaced the probe fast-on, but the butt splices are more reliable... When properly crimped.

Vern

 

[Dynon]

What's the vintage of those probes? We've made a few running changes over the years on different aspects of the probes, and improving the crimp quality was I believe one of them.

 

[vlittle]

Shipped to me Oct, 2011 from PCA.
Vern

 

[jakej]

Vern
That's exactly the same situation I've been posting about on this forum in the past - glad you got it nailed as well ;D

Jake J

 

[vlittle]

I saw that others had problems, but there was no analysis of the root cause. I micro sectioned the egt crimp terminal and it was clearly not done in accordance with proper industry practice.

Single crimp teminals and not enough insulation stripped was the root cause. Maybe Dynon should hire Bob Nuckolls... Seriously...

Vern

 

[mmarien]

Crimping turns out to be the problem in Vern's case. He only has 37 hours on the TACH. If something is going to fail it'll probably fail early in it's life span as did the improper crimping in Vern's case. My probes lasted a couple hundred hours and began to fail when I installed fuel injection and started running the engine slightly LOP. The EGT probes I was using couldn't take the heat. The problem was solved with a little higher quality probes.

So the connections are an obvious place to start looking, but not necessarily the culprit. 

Also, if you read any articles about EGT's you may want to remove the yellow and red from the top of the EGT gauge and leave it all green. There is no upper (or lower) limit to EGT. They do peak at some point but it's not dangerous to run the engine at peak EGT.

 

[jdubner]

Another data point:

I've suffered with a single "flakey " EGT indication (#4 cylinder) for some time.  By "flakey" I mean it would read low or not at all (a red "X" in place of a numerical indication).  I've even posted about it on this forum: http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1406507262/0#0

I've recrimped the probe connection to the EMS cable three times using proper terminals and techniques.  Afterward, the indication would be normal for a short time but then become "flakey" again.  And then the indication would appear to operate normally again, until the next time it went "flakey".  Frustrating.

It must be a defective EGT probe because my connection technique and the EMS itself are no longer suspect.  To hold down work and expenses, I'd like to replace this probe with a higher-quality one but I'm hesitant to do so because of incompatibility issues I've read about on this forum.  So the next time I have the lower cowl off and a couple or three hundred spare dollars, I'll buy a set of four and replace all of them :-(

--
Joe