The #1 EGT probe on my Jab 3300 has become slightly erratic.  It occasionally fluctuates quite a bit, but never goes completely out.  The probe has 730+ hrs and I'm guessing it might simply be wearing out, or, perhaps I've got some corrosion or poor contact in the wiring connectors, etc.

Just wondered if anyone has seen this and is a probe failure usually an "all or nothing" event or do erratic fluctuations predict imminent failure?  Obviously I don't think the fluctuations are actual EGT readings as the engine is running great and the CHT of #1 is right where it has always been.

I'll be pulling the cowl soon and checking it out - fortunately I have an extra probe on-hand should replacement be necessary!


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Most likely connection issues, junctions or at input connection.

I'm totally ignorant about the Jab (and most things!), so take this for what it's worth, but could it be an ignition problem and not a sensor fault?

I would expect a totally erratic pattern to be a sensor fault, but if it's fluctuating between two temperatures, that might point to something else.

For example, if one of the spark plugs isn't firing consistently, that could cause intermittent high EGTs because fuel would still be burning when the exhaust valve opens. That might not make a noticeable difference in the engine's performance because the cylinder's other plug would be (mostly) making up for it, and there are five other cylinders.

If the EGT fluctuates both low and high, a single spark plug probably isn't the issue, but if your engine monitor can output a graph of EGTs over time, someone who knows more about these things could probably narrow down the problem after a quick look at the graph.


It's a totally erratic pattern and so far no problem with one ignition vs the other on mag checks.  The CHT is stable and same as always. The engine runs smooth as silk, so really doubt an ignition problem. Also, the erratic jumping is instantaneously hundreds of degrees different so hard to believe the EGT could vary that much instantly. 


Makes sense. It sounds like swapping out the probe will either fix it or show that something has come loose.

John,  I had one go out a couple years ago (~150hrs) - totally died.  No other erratic readings, so pulled it out and heated it with no indications - replaced and has worked fine so far 350 hrs.  Jim 


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