Jump to content

EGT probe again!


Rich

Recommended Posts

I would sure like to know why the #'s 1 and 3 EGT probes fail so often.

So far, with 197 hrs TTE, I've eaten up 4 probes. Two on each of the above mentioned cylinders.

I've had two from the dealer and two from TruTrac .

 

No failure had occured on 2 and 4. (as yet.)

 

This seems too often. The last new probe lasted about 25 hours on #3.

 

Hasd anyone else had this experience?

Link to comment
Share on other sites

When you pulled the  EGT, did they look burned through? They can have coke buildup. Burning indicates something is up and they are taking TOO MUCH heat, and your indicator isn't working right or your wires are too high of a resistance. Unlikely for all this to go wrong at once though.

 

How are you suspending the wires? You need to have a short droop loop as they come out of the probes, and tie them off closeby. Too short of a droop loop, and engine vibration will tug the wire. Too long, and now you have a wire whipping around. Both are a lot of strain on the connection. This is most likely your problem.

Link to comment
Share on other sites

Anti,

 

I'll check the loops next time out. I did not pay attention to that when I installed them. Thanks for the tip.

There was some build up of carbon on each but nothing major. No burned areas. Probes came out with just a little wiggling.

Plugs looked fine. Carbs balanced. Engine runs very smooth.

 

Thanks

Link to comment
Share on other sites

Hook up a voltmeter to the bad probes. Take a torch to the probe end and warm it up. Voltage should change on the voltmeter, increasing as it gets hotter. It won't be an indication that they are good, just an indication if you have a broken wire (no change).

 

Someone might ask so I'll also mention: oil temp probes are thermistors, and in this case, are configured so that the hotter they are, the lower the resistance. You use an ohmmeter to test them.

Link to comment
Share on other sites

Very few airplanes I have flown even have EGT probes and indicators.  Does FD use that to automatically adjust mixture?

 

Rotax with carbs (Bing) have automatic altitude compensation.  The probes just provide engine info for EGT and CHT.  The 912si is a whole 'nuther animal.

Link to comment
Share on other sites

That's why I have an infrared thermometer. Had a rough running engine on a carbeurated warrior, lightly tapped the cyl 1 exhaust while running and didn't feel any heat. Touched it, still no heat. Grabbed it and still nothing. Thought I must be stupid and grabbed Cyl 3 pipe to see. The burns proved I am stupid. (I had a derp moment!)

 

Cyl 1 vacuum intake leak. For those that don't know what this is about: carb on a O-320 is shared on all 4 intake pipes. Intake leak meant that air wasn't being sucked from the carb, it was being sucked through the leak. So very little fuel was making it to the cylinder.

Link to comment
Share on other sites

Hook up a voltmeter to the bad probes. Take a torch to the probe end and warm it up. Voltage should change on the voltmeter, increasing as it gets hotter. It won't be an indication that they are good, just an indication if you have a broken wire (no change).

 

Someone might ask so I'll also mention: oil temp probes are thermistors, and in this case, are configured so that the hotter they are, the lower the resistance. You use an ohmmeter to test them.

 

Anti,

 

What would be the voltage scale to set on the multi-meter. Flipping the switch is no big deal but I thought you might know.

Also, thanks for the other information----------Rich

Link to comment
Share on other sites

Hamburger,

 

Why would you leave your plane 150 miles away if only one EGT probe went bad?

 

Because it was a warranty issue and Rotax said to not fly it until it was examined by an A&P and repaired.  The field we landed at let us borrow a hangar for the two weeks it took to get the part and have an A&P fly out and do the repair.

Link to comment
Share on other sites

EGT's are nice to have, but many planes don't have them. EGT's can help diagnose a problem if they are on all 4 cylinders, but our CT's are usually on just the rear two cylinders #3 & #4 and could still narrow the diagnostics down.  If you have an older CT or in Europe you may have a Flydat instrument that has all 4 EGT's. EGT probes should be positioned 100MM or 3.9" out from the exhaust flange for the proper temps. Too close causes high temp readings and possible burnt probes and too far causes cooler than normal readings. A failed EGT probe shouldn't be a reason to ground a plane. You still have all the other instrumentation that should give you an indication of something wrong other than just a bad probe. As Corey said a probe can be checked with a voltmeter. I usually carry a couple extras in the shop (around $35). The CT probes are easy to replace as they are plug and play type installation.  Dynon told me they should last to at least 200 hours, but obviously some have failed a little sooner, but many may go 1000 hrs. -TBO without any issues. It's just the luck of the draw. You can cause an early failure if the wires get pulled on too much while someone is under the cowl.

 

Rotax wouldn't have any comment on the probes since they aren't required or supplied by Rotax and they are under the installation guise of the aircraft MFG  or owner/builder and in the CT case, FD. Rotax does not warranty EGT probes. I think someone may have given you some bad advise on grounding yourself because it would not have affected any warranty to fly home without one EGT probe. It was covered either way and wouldn't cause any damage. It's just a temp probe that was backed up by all the other instrumentation feedback.

Link to comment
Share on other sites

Grounding a plane because of a failed EGT probe just seems odd to me.

 

EGT can be handy for diagnosing problems, but with no mixture control not of much use in day-to-day operations.

 

Far cry from a Cirrus, let's say, where EGT is invaluable for both LOP and ROP operations.

 

I'm happy not having them in my plane - one (four?) less thing(s) to go wrong!

Link to comment
Share on other sites

EGT's are nice to have, but many planes don't have them. EGT's can help diagnose a problem if they are on all 4 cylinders, but our CT's are usually on just the rear two cylinders #3 & #4 and could still narrow the diagnostics down.  If you have an older CT or in Europe you may have a Flydat instrument that has all 4 EGT's. EGT probes should be positioned 100MM or 3.9" out from the exhaust flange for the proper temps. Too close causes high temp readings and possible burnt probes and too far causes cooler than normal readings. A failed EGT probe shouldn't be a reason to ground a plane. You still have all the other instrumentation that should give you an indication of something wrong other than just a bad probe. As Corey said a probe can be checked with a voltmeter. I usually carry a couple extras in the shop (around $35). The CT probes are easy to replace as they are plug and play type installation.  Dynon told me they should last to at least 200 hours, but obviously some have failed a little sooner, but many may go 1000 hrs. -TBO without any issues. It's just the luck of the draw. You can cause an early failure if the wires get pulled on too much while someone is under the cowl.

 

Rotax wouldn't have any comment on the probes since they aren't required or supplied by Rotax and they are under the installation guise of the aircraft MFG  or owner/builder and in the CT case, FD. Rotax does not warranty EGT probes. I think someone may have given you some bad advise on grounding yourself because it would not have affected any warranty to fly home without one EGT probe. It was covered either way and wouldn't cause any damage. It's just a temp probe that was backed up by all the other instrumentation feedback.

 

Not in this case Roger.  In the CTLSi the enunciator lit up while flying between KRNO and KVGT.  Luckily I was close enough to KHTH to do an emergency landing.  Once on the ground I turned the plane off and tried to restart, the light remained on.  Then noticed one of the EGTs was low.   A call was made to Lone Mountain who then talked to California Power Systems (Rotax West).   CPS told Lone Mountain who then told us not to fly the plane.

 

The nice people at KHTH loaned us a hangar which was critical since the winds at KHTH were to become ferocious.

 

Lone Mountain flew from KVGT to KHTH where the plane was grounded about four days later and dumped the ECU.  They then flew back to KVGT and sent the ECU dump to CPS.  At that point the diagnosis indicated a dead EGT probe.  The probe was ordered thru CPS, delivered to Lone Mountain who then flew back to KHTH and made the repairs. 

 

We were told that a Rotax part was used, and Rotax covered the labor and part under warranty.

Link to comment
Share on other sites

On the fuel injected engine are the EGT's just for instrumentation, or do they provide information to the computer that controls the engine? I don't know for sure, but I suspect that the EGT information is an important element for the ECU.

Good point - if so, that makes all the difference in the world and I take back what I said about grounding the plane being odd.

Link to comment
Share on other sites

Anti,

 

What would be the voltage scale to set on the multi-meter. Flipping the switch is no big deal but I thought you might know.

Also, thanks for the other information----------Rich

 

Lowest you can go. These push on the magnitude of millivolts. Need to use a pretty sensitive meter.

 

As for EGT for the ECU: I don't recall if it uses EGT. You can bet it has a narrow "safe band" for all sensors though. If it falls out of expected EGT range and it's a factor in the fuel map (not manifold air pressure, an actual map of values), it would only change the fuel flow up until a certain "safe point"

Link to comment
Share on other sites

It's easy to check and see if you just have a bad EGT probe. Swap the wire on the suspected bad EGT and see if it still remains. If an EGT is truly showing an issue it will also show up somewhere else. It won't be a singular event. If something happens to an engine to cause the EGT to take a major dive then something else has to be evident. For example a bad running engine (vibration), CHT changes, oil temp changes, ect...

If a probe goes bad many times you will get XXX for a reading or a -99. If you have either of these two it is the probe or a wire.

 

The 912is engine does have 4 EGT probes from the factory. 

Link to comment
Share on other sites

I believe they are wired to help control the system, but I'm not 100% sure. The 912is engine still has me on the upward learning curve. I just don't see any. One at my field, but haven't spent any real time with it. Did the Sport upgrade, but it hasn't had any problems so I could play.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...