EGT Sensor Problem

[mmarien]

I started having an issue with a couple of my EGT probes. They seem to work some of the time. Once in a while they read really low - 20C when the other two are normal. I don't have a screen shot but will get one next time I see that.

Since I put in the electronic fuel injection my EGT's have been really high. I spent a lot of time researching and decided to believe Mike Busch when he says that EGT's can't get too high to do any damage in a normally aspired engine. I just took out the top yellow and red areas of the EGT gauge so I don't sweat it.

http://www.gami.com/articles/egt_myths.pdf

So the question is, can EGT's get too high to damage the sensor? what does the sensor show when it's fried? Here is a shot before I modified the gauge. Ignore the AFR VOLTS. It wasn't working for this shot.

 

[skysailor]

The voltage seems very high for a 14V system. That should not have hurt the probes but does the system go back to normal when the alternator is turned off?

 

[DBRV10]

The EGT is OK, but at that MP and RPM....what is really going on?

The sensor will cope with those temps no problem, a TIT is 1600F + so don't stress.

So does your electronic fuel injection have a good weapon against detonation??? Like it should.?

Something like PRISM for example?

This is not a motor car, and I gather it does not have any knock sensors either?

I suspect the EGT you are seeing at those MP and RPM mean you have a nice case of medium detonation going on, or maybe more.

The bottom line here is, -20 indicates a loose connection or maybe a failed probe, but that is not from 1600F, but that kind of EGT suggests the probes are telling you something of the combustion event.

That is something I would be worried about.

Post a data file, lets examine it!

 

[mmarien]

Skysailor

I thought the voltage was high so I took the alternator back. The shop claims that is normal voltage. My old alternator was set the same way. I turned the regulator down to 14.1 but this is a new alternator with a built in regulator. I did the research and even posted here but didn't find anything different on the voltage. Here is a screen shot of VP-X. The voltage stays a rock solid 14.7 volts with the engine running. It's 12.5 +/- with the engine off.

Most new equipment tolerates 12-30 volts so I'm thinking it's fine.

David

This shot shows the AFR working. It about 14.1 which is rich of peak EGT. Peak EGT would be 14.7 AFR. I get a higher ratio at 65% power but it's in the 13's when I push it into the 80% range. That's probably an indication it enriches with more power.

I'm thinking detonation would be indicated by runaway CHT. The EGT are high but notice in both shots the CHT are a nice 340F-380F.

So you're saying the probes may be shot? It's intermittent so I'll see if I can record when it happens.

 

[dynonsupport]

So when the thermocoule junction opens up behind the metal sheath, the EGT number will float. So your -20 reading could be that. It could also be an intermittent connection.

More generally, "high" EGT values in th 1600s get you to the point where the metals in the EGT probe junction soften. So higher EGT values will definitely shorten the EGT's life.

 

[dynonsupport]

I should also mention that there are EGTs out there that may be more tolerant to higher heat than the ones we sell, but they'll cost you more too ($100ish vs our $36). We try to find the right balance between economy and performance.

 

[mmarien]

Thanks. If the EGT's probes keep acting up, I may look for different ones. For now I'll just keep an eye on them.

 

[jakej]

You've probably checked but look at the (removed) connector on the EMS module, the pins will move in & out with when flexing the bundle of wires. Sometimes 1 or 2 will stay partly retracted resulting in the same type of symptoms - just saying

Jake J

 

[mmarien]

It's intermittent but I was thinking a non connection is usually max display not minimum. Worth a check for sure. I can probably reach the connection in flight if I have a copilot when it happens next.

 

[dynonsupport]

Thermocouples are a differential sensor and can go any random direction when disconnected.

 

[mmarien]

Some screenshots of the EGT's. First is on the ground and then 15 and 16 minutes into the flight.

Notice the green grass runway. It showed up when I switched to PocketFMS. The airport was there with Jeppeson, but not the runway in SV.

 

[DBRV10]

Looks like some loose connections. As Jake and I have both found, the pins in the connector are pulled out as the harness bends in the connector. The EGT cable is stiff and does not bend easily.

We have had this on our 6 probe setup.

Can you do me a favour ..... use degrees F Even us metric Aussies like our aviation temps in F :-?

 

[mmarien]

I tried Fahrenheit but all the temperatures were nearly twice as hot.

If you remember the discussion on round gauges a while back, general consensus was that it didn't matter what the numbers were, it was the position of the indicator that they were looking for. The original EGT gauges didn't have numbers. Just a star at about 2/3 position. Personally I like to see gauges in the middle of the green. Yellow or RED get my attention right away. That's why I got rid of the upper yellow and red on the EGT's. It scared the bejesus out of me every time I looked. Now it's green right to the top. I also added 100 degrees to the top end so the indicators weren't so close to the top all the time. Top is now 1700F instead of 1600F.

I think Jake pointed me in the right direction. I spent some time checking all the connectors on the engine side before I posted, but didn't look at the DSub connector at the EMS. It's probably a good place to check before I start thinking about replacing sensors although replacing sensors on the engine side would be a lot easier then crawling under the panel to check the plugs on the EMS. I need a skinny guy with both arms on one side.

 

[jakej]

mmarien,
"It's probably a good place to check before I start thinking about replacing sensors " -- That's the first place to checkin this situation IMHO, don't you just love the access with the glasair :

Jake J

 

[mmarien]

Ok - I think I fried them all. Last one was working a few minutes ago and now it's fried. I might have considered a wiring problem, but since the CHT and EGT wires are next to each other (CHT4 wire is D25p6 and the EGT4 wire is D25p7) I would have thought I'd have a CHT failure and then an EGT failure. I can't see having a loose EGT wire between two CHT wires that aren't loose.

Anybody have any suggestions for a more heat tolerant EGT probe that will work with Skyview? Aircraft Spruce has 198 matches for EGT probe.

 

[jakej]

Murray

I really don't think you have 'fried' them - that many just don't fail at the same time, I've only ever replace 1 x Egt & no CHT probes & I've installed a lot of them

Flexing the bundle of EGT/CHT cables can, & most likely will, result in the symptoms you're seeing.

What I do with all installs now is remove the backshell and heatshrink then, starting from the centre of the dsub connector, bend the wires as necessary to 'strain relieve' them before refitting the backshell.

ps. you should bend the loom if you need to get around corners before the next step.
Then I use lacing cord around the loom every 2" for at least 8" from the connector to reduce the chance of them moving inside the shell.

HTH - but it won't make it easier to work on the Glasair ;D

When I redo mine, it was done 19 years ago, access will be a lot easier too.

Jake J

 

[mmarien]

Jake

They went one at a time. It's a winter project to replace them so I'll probably have a look at the wiring before I replace the probes. I have a loop right off the EMS for strain relief. I guess I can check the probes by connecting an analog gauge directly and lighting a match under the probe. While I can do some testing, I think the probes just couldn't handle the sustained 1550F+ degree heat. I check last years screen shots and couldn't find many EGT's over 1450F. Same probes but I wasn't running this close to stoichiometric combustion before.

 

[BClulow]

Just had a 100hr done on the Carbon Cub and when I cranked it up noticed cylinder 4 EGT was a negative number, while the other exhaust temps after warmup were normal. The EGT value on sensor 4 floats all over the place, any idea's? Is this a faulty sensor, it seems strange that it happened after the 100hr, it was working fine before that. How fragile are the sensors, could a bump while working on the engine cause a sensor to fail?

 

[jakej]

The EGTs are fairly robust however they could be accidently damaged (though I don't know of this happening) but unlikely IMO. Most of the 'issues' are to do with the connections at probe side or other side, sometimes the pins retract at the SV EMS end.
Some of the earlier ? probes had a single conductor which had a poor crimping result evidenced by movement between the wire and terminal. If that is the case then cut off the terminal and double over the wire before crimping on a new one. Later probes have a multistrand wire which gives better results.
HTH

Jake J

 

[mmarien]

In my search for replacements for my EGT sensors, I've seen the term consumables used. :-?