Strange #2 CHT Temperature Issue

Post by **bullojm1** » Sun Feb 06, 2011 2:55 pm

Here is an interesting thing I noticed on my RV today. I was running at about 65% (2310RPM / 20.4") and leaned out to around 7.8 to 8 GPH. Everything is fine and the engine is puttering along nicely. Then I notice my CHT for #2 is fluctuating quite(actually a lot) a bit more than the other cylinders. The max temp it about 330 degrees, or what the other CHT's are, but the minimum goes down to the low 200's.

Immediately I thought it was a bad sensor. So for fun I enriched the mixture and low and behold the CHT stabilized. And stayed stabilized! So I ruled out the CHT temp sensor being bad because it would be bad all the time.

I am really stumped on this one. The only things I can think to check are as follows:

1) Induction Check (Done, no obvious leaks)
2) Fouled Plug(s)
3) Clogged Injector
4) Another issue a compression check would find.

The thing is the engine sounds and runs fine. No sputter. Nothing. I would appreciate any idea anyone has!

Wicked Stick · Post by **Wicked Stick** » Sun Feb 06, 2011 9:46 pm

Check for a loose connection to that sensor is the first things that come to mind looking at how radically it changes in a short period of time.

Let us know if you find out the cause.
Perhaps also try to repeat the event as well to see if it reocurrs.

Post by **bullojm1** » Sun Feb 06, 2011 10:00 pm

Dave,

The more I think about it, the more I think it has to be the sensor. With the drastic CHT change should come SOME sort of a EGT change. But nothing. EGT's are straightline. I might order a new CHT sensor this week just to be on the safe side.

dons · Post by **dons** » Mon Feb 07, 2011 9:08 am

Having not got this far I don't how easy this would be to do, but when I suspect a sensor of any kind, I swap it for a known working one (like from one of the other cylinders in this case). This should help narrow down the problem between the cylinder, sensor, or even wiring from the sensor to the controller or connector right in the controller. If the mechanical vibration changed between lean and rich, it very well could be a connection issue that only appears in a small range of vibration frequencies. Wiring splices (sometimes right at the sensor), and connectors are the most likely source for what you are seeing, in my opinion.

airguy · Post by **airguy** » Mon Feb 07, 2011 9:32 am

bullojm1 wrote:Dave,

The more I think about it, the more I think it has to be the sensor. With the drastic CHT change should come SOME sort of a EGT change. But nothing. EGT's are straightline. I might order a new CHT sensor this week just to be on the safe side.

I'm thinking sensor for another reason - the actual temperature of the cylinder changes fairly slowly, due to the mass of the metal that must be heated/cooled. I don't think it's physically possible for the trueCHT to be changing as rapidly and jaggedly as your CHT trace indicates, in only a 2-minute time window.

Post by **bullojm1** » Mon Feb 07, 2011 2:29 pm

I think I just had one of those "DOH!" moments. On Saturday night I was messing around installing a better version of my blocking plate for the oil cooler. In doing so I needed to re-attach the adel clamps which hold the EGT and CHT probe wires for the #2 and #4 cylinders.

If you look closely at the wire label between the two adel clamps, it says "CHT 2" on it. Seems to be this could be a loose connection!

Post by **Spike** » Tue Feb 08, 2011 9:38 am

That is definitely a good place to start looking dude.