What Could Cause CHT Blips

[Dynon101]

I was reviewing the SAVVY data and noticed that mostly the CHT readings are stable however fairly often in an unpredictable pattern 5 of the 6 CHT indications "blip" up for a few spikes and then go back to their normal and expected values. During these blips there was no change in MAP, FF, IAS, ALT, Turbulence . So 5 of six CHTs will all not spike up at the same time.

What could cause this?

Incidentally, oil pressure indication was rock solid during these flights with blips and then just on the last two flights it is very erratic and bumps around from -21F to 240F in complete static fashion.

:-[

 

[preid]

Unfortunately I too have recently started seeing this as well. At one point I thought maybe I had a short as the CHT spikes numerous times when I was calling tower, but yesterday while cruising along not doing anything it did it a few times than 5 minutes later did it again, than it was fine for over an hour and did it again..
I was about to go to the airport thinking maybe I had a few bad probes go out on me, including one I just replaced.
Maybe a short or a grounding issue that has developed with erratic behavior?
I'll replace one of the probes and see if it continues, if it does it is not a probe issue.

 

[mmarien]

If you are getting a number of sensors acting up, it might be worth while looking at the D-Sub connectors on the EMS. One of them could be loose causing poor connections.

 

[Garrett]

I just had that happen with my EGT changed the probes and problem solved.

 

[Dynon101]

Thanks for the information.

It seems unrealistic for all EGT probes (less one) to be all bad because they spike at the exact same time and the spikes are intermittent..with no fuel flow or MAP delta.

The D sub could cause this... I'll look into it.

Any help one else have this problem?

 

[dynonsupport]

My first guess would be RF transmissions. Pay attention when you transmit on the radio, or try turning off the transponder.

If it's that, then we can look at how to solve it.

 

[Pobb]

I have two EGT probes that jump around between having a red X against them, or are indicating temperatures fluctuating between a minus figure to maximum temperature.  I have swapped the faulty probes on to the other two known good circuits and they still play up, while the good probes are quite happy on the EMS circuits that are normally connected to the faulty probes.

I thought that I may have had dodgy connectors on one probe so I cut them off and re-terminated the leads, but had no joy with that.  Looks like I will be up for two new probes.

 

[Garrett]

I changed them all because I did have one failing intermittently so I changed them all, I figured the rest can't be far behind. They have a finite life.

 

[rogersmart]

mine were corrected with inline suppression of some type supplied by Dynon, between the efis and the d connectors

 

[Dynon101]

arpb says>mine were corrected with inline suppression of some type supplied by Dynon, between the efis and the d connectors

Would you please be so kind as to elaborate??? What is inline suppression?

 

[NASA515]

BINGO!  I think I just solved a long nagging problem.

My problem is not CHT. but EGT blips  I have lived with them for a couple of years (SV Touch, latest Firmware.)  (I have had poor service life from the EGT probes - that is another problem not discussed here.)

I download and review all my flights on Savvy.  I noticed these blips (Rotax 912) both LH & RH EGT.  First, I thought they were just some sort of intermittent connection and did a lot of wiring and connection checking (RV-12 has known problems with EGT spade connectors.)  But the problem persisted. 

I couldn't explain both sides spiking simultaneously, although the spikes were not always of the same magnitude. I thought I might have an ignition problem (although there are two ignition modules.)  Eventually, I was concerned enough to buy a one year subscription with Savvy and discussed the problem with one of their analysts.

After a lot of analysis, he was able to pinpoint a correlation between the generator output amps and the EGT spikes.  Every time the EGT spikes, there was a downward spike (discharge) in Amps.  We discussed generator wiring and voltage regulator impacts, and he suggested I work in those areas. 

The Ducati Voltage Regulator is a well known problem on the RV-12 Rotax  installation.  I wrung out all the generator wiring, installed additional grounds between the engine and the airframe, and rechecked the V-R wiring.  I worried a bit about the generator having an intermittent short.  If it was an intermittent V-R, well, I knew how to solve that and purchased a spare.

Based on the comments above, I think I know what the problem is - EMI from the radio.  When I key the mic, the radio (Garmin SL-40)  sucks the amps and the EGT spikes.  I went back and reviewed a number of flights.  I can see the Amp / EGT spikes occurring regularly, for example, during my approach and landing, as I announce downwind, base, and final in the pattern.  Also, during my takeoffs and climbouts when I self-announce, or call ATC.

The enroute spikes seemed, and were, random.  That's because my talking with ATC is quite random and difficult to trackdown (I use Flight Following extensively.)  But the departure and arrival spikes were all clearly identifiable.

Yippee!  Well I feel I have now positively identified and solved my problem.  Well, not "solved" exactly, since there is still an EMI impact on EGT via the radio.  But at least I now know that I don't have some sparking connection somewhere in the generator charging circuitry.

Bob Bogash
RV-12 N737G
400 hrs

 

[mmarien]

I have had poor service life from the EGT probes - that is another problem not discussed here.

It was discussed quite a bit a couple of years ago. I believe Dynon said that they were looking into better quality probes as it was an issue at one time. I fried all of mine just after I installed electronic fuel injection and ended up replacing them with higher quality probes. I looked for ones that claimed 2000F. They have blade connectors installed with a good ratcheting crimping tool. No problems for the last 350 hours. 

 

[NASA515]

Not discussed "here", as in this posting, not in general. I'm well aware of the ongoing discussions regarding the probes.

Bob

 

[jakej]

Good tools & good connectors fixes most problems people are seeing  & are the cheapest option in the long run IMO.

 

[NASA515]

MOST of the problems, but not all. I've spending many hours working my connectors and ensuring they're as perfect as they can be.

Bob

 

[jakej]

Hey Bob, I believe you - my comment was just a generic one coming from someone who has done many installations

 

[planecurious]

Bob:

This is a well-known issue with SkyView. Call Dynon Avionics Tech Support and tell them you get EGT jumps during COM transmissions. They can usually ship you a replacement SV-EMS-220 in advance to swap out your current unit.

BINGO!  I think I just solved a long nagging problem.

<snip>

After a lot of analysis, he was able to pinpoint a correlation between the generator output amps and the EGT spikes.  Every time the EGT spikes, there was a downward spike (discharge) in Amps.  We discussed generator wiring and voltage regulator impacts, and he suggested I work in those areas. 

The Ducati Voltage Regulator is a well known problem on the RV-12 Rotax  installation.  I wrung out all the generator wiring, installed additional grounds between the engine and the airframe, and rechecked the V-R wiring.  I worried a bit about the generator having an intermittent short.  If it was an intermittent V-R, well, I knew how to solve that and purchased a spare.

Based on the comments above, I think I know what the problem is - EMI from the radio.  When I key the mic, the radio (Garmin SL-40)  sucks the amps and the EGT spikes.  I went back and reviewed a number of flights.  I can see the Amp / EGT spikes occurring regularly, for example, during my approach and landing, as I announce downwind, base, and final in the pattern.  Also, during my takeoffs and climbouts when I self-announce, or call ATC.

The enroute spikes seemed, and were, random.  That's because my talking with ATC is quite random and difficult to trackdown (I use Flight Following extensively.)  But the departure and arrival spikes were all clearly identifiable.

Yippee!  Well I feel I have now positively identified and solved my problem.  Well, not "solved" exactly, since there is still an EMI impact on EGT via the radio.  But at least I now know that I don't have some sparking connection somewhere in the generator charging circuitry.

Bob Bogash
RV-12 N737G
400 hrs

 

[NASA515]

Thanks, working with them now.

Bob

 

[mrdaud]

Posted this on a previous thread, but worth doing again here.  I have had a lot of problems with the thermocouples!!!!  Some, with what I think is poor quality of the actual thermocouple, and others with poor connections using the spade connectors.  Working in the pharmaceutical manufacturing industry, I decided to use dedicated, specific-built connectors I have used in past manufacturing applications.  I order most of my temp/pressure/recording equipment from Omega.  Since switching to the thermocouple designed connectors, I have had no issues, except for the occasional  EGT thermocouple meltdown.  The cost of the connectors is less than $3 each, but is well worth the additional expense vs. spade connectors.  They are about 1/2" wide.  The connectors are specific for J and K TC's, and should be bought in male -female pairs.  The Ks are color coded yellow, and the Js are black.  Here is the link: http://www.omega.com/pptst/SMPW-CC.html