One CHT probe going negative?

[gtae07]

Started my engine for the first time this past weekend. CHT #4 started at ambient temperature like the other probes, but then started trending negative the warmer the engine got until the other three were in the 180 range and it was reading -25. Eventually it dashed out. Pretty sure today with the engine off it was back at room temp.

Before I completely tear my hair out, my thoughts were along the lines of either reversed wires or a bad crimp at the spade connector. Anyone else run into this one before? I only found a couple hits in a search but no firm resolutions.

 

[swatson999]

Nothing is very hard to check here, not to mention, you're going to have to do it anyway. Just check the pinout for the #4 CHT wires to validate correct wire colors, then if ok, proceed to the connector and do the same, check the crimp, and lastly make sure you've selected the right sensor in the EMS setup.

It's certainly not going below freezing, so that leaves sensor, wiring, or configuration. May as well dive into it, it ain't THAT big a deal.

 

[SV_Classic]

Started my engine for the first time this past weekend. CHT #4 started at ambient temperature like the other probes, but then started trending negative the warmer the engine got until the other three were in the 180 range and it was reading -25. Eventually it dashed out. Pretty sure today with the engine off it was back at room temp.

Before I completely tear my hair out, my thoughts were along the lines of either reversed wires or a bad crimp at the spade connector. Anyone else run into this one before? I only found a couple hits in a search but no firm resolutions.

reversed wiring will do that, if it was just a bad crimp it wouldn't be doing anything. good luck with it

 

[swatson999]

reversed wiring will do that, if it was just a bad crimp it wouldn't be doing anything. good luck with it

Actually, a bad crimp will give you wildly jumpy readings, until it goes to zero when it fails to make contact entirely. Ask me how I know this. Recrimping the connector is only a temporary solution. I ended up going with the Omega thermocouple connectors and have had zero issues with them for many years now, after several instances of crimped connectors acting up.

 

[gtae07]

Turne out that yes, the wires were swapped at the terminals

Not quite sure how I managed to put white to red and red to white, but there you go.
I'll confirm the temps next engine run.