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My EGT's have risen 100 degrees!!

pierre smith

pierre smith

Well Known Member
...during the last two flights. After balancing the injectors up at Airflow, everything was cozy and I happily ran 50 LOP with EGT's around 1420 or so. All of a sudden, they're reading 1560 and the numbers turn yellow on the D-120. In the past, the hottest they'd get was around 1460-1470, then start dropping going LOP.

Methinks I have a couple of bad probes since only two cylinders do this while the others are 125 deg cooler. They're three years old with 350 hours on the airplane.

What say you?

Thanks,
 
Fuel flow and CHT's still consistent with what you're used to seeing? May be bad probes, however if you're seeing this immediately after balancing the injectors..... ??? One EGT probe going I could see, however two at the exact same time? I'm no math major but statistically that's a stretch.
 
Seems like one plug in those high egt cylinders is not firing. If one plug stops firing, it is somewhat like retarding the timing.

I know if I turn one ignition off, the egt's go way up also.
 
Possible induction leak? Is your manifold such that you could have a leak that would only affect those two cylinders driving them leaner? Do they all still hit peak at the same fuel flows as before?
 
Restricted injector (dirt) would make EGT go up normally, but maybe not when LOP. Fuel flow would maybe stay the same with "lost" fuel from the 2 restricted injectors going out through the other 4 cylinders. That would change CHT's & EGT's on the other 4. LOP is almost like region of reverse command. Do your temps & fuel flow indicate this?
 
probes

If memory serves, I think probes generally fail lower rather than higher. Does any one else have any thoughts on that?
 
The mag checks good...

...during runup and so does the Lightspeed.

The CHT's on those two cylinders are also close to the others and cooler than a couple as well. The cowl's coming off today for a closer look...maybe it's whispering in my ear, huh?

Thanks,
 
pierre smith said:
...during runup and so does the Lightspeed.

The CHT's on those two cylinders are also close to the others and cooler than a couple as well. The cowl's coming off today for a closer look...maybe it's whispering in my ear, huh?

Thanks,
Click to expand...

Pierre - is it possible that the two cylinders are both on the same Lightspeed coil? If so, that coil might be flaky. Since it is a wasted spark system, each coil fires two cylinders.
 
You didn't wrap any of the exhaust pipes recently, did you?? During annual, I wrapped one that was close to the fuel transducer. Was scratching my head afterwards why that one cylinder went high on egt only. I pulled top cowling to investigate, looked at the wrap and went DUH!!
 
Alcor combustion analyzer troubleshooting guide

Here's a link to the Alcor document in the post title. http://www.alcorinc.com/pdf/netsc013.pdf

It says the following:

EGT symptom: 75 - 100 rise for one cylinder
Probable cause: Spark Plug not firing due to fouling, faulty plug, lead or distributor.
Recommended Action:
1) Enrich mixture to return EGT to normal
2) Go to single mag operation. When mag firing the bad plug is selected, EGT will drop suddenly, defining plug is not firing

I think the trouble shooting is the same for two plugs not firing, but to do the mag test it will need to be in the air when the EGTs are high so you can see the change.
 
You get a "A" Alex...

AlexPeterson said:
Pierre - is it possible that the two cylinders are both on the same Lightspeed coil? If so, that coil might be flaky. Since it is a wasted spark system, each coil fires two cylinders.
Click to expand...

I connected with Klaus at Lightspeed and also noted that cylinders 3 and 4 do indeed share the same coil...the cylinders with the high EGT and cooler CHT's.

I have two coils shipping overnight....one as a spare.

Thanks guys...I'll let you know tomorrow evening.
 
Pierre,

Just curious- where are the coils mounted on your installation? Are they atop the engine, or outside the plenum in the "cool" area. And how many hours are on the installation when the coil failed?
 
The coils are mounted on top...

...of the engine, towards the rear. I have two on the way, one as a spare since they're only $89 each. The "brain" is inside the airplane behind the instrument panel. The airplane and engine have around 350 hours total.

Klaus asked me if I'd checked my ignition systems in flight and I said no and that they had checked good during the 1800 RPM mag check.

Interestingly, he said that you troubleshoot a problem while you're having the problem, not when there's no problem!! Ray, my friendly A@P/IA buddy and I had to think on that for a second or so but Klaus has a good point.

I decided to fly the 24 miles back home at reduced power settings and interestingly, at 22" and 2300 RPM, there was no problem and I leaned down to 11 GPH on the Dynon 120 and all EGTs were very close. I was also getting a surprising 14.5 miles per gallon with a slight headwind.

Don, at Airflow Performance had told me a few weeks ago to lean to the most efficient point..MPG. At that point, however, I was going around 170 MPH and I said that that was all well and good but I didn't buy this fast airplane to go slow! It was a good learning experience though, showing that I can get very near the hourly fuel burn of my 0-360 in my old -6A.

Best,
 
pierre smith said:
.... Klaus asked me if I'd checked my ignition systems in flight and I said no and that they had checked good during the 1800 RPM mag check.....
Click to expand...

The guys at Advance Pilot Seminars (George Braly, John Deakins, Walt Anderson, et. al.) advocate doing your mag check at the end of each flight while you're still flying WOT and LOP for a couple of reasons:

1. They claim that doing a mag check while WOT LOP will uncover problems that a simple ramp check at 1800 rpm simply won't show as the ignition system is having to perform at its peak to ignite the fuel in this configuration.

2. If you do find something's wrong, you can get it fixed before your next flight instead of having to deal with it as you're ready to take off.

I certainly don't claim to be an expert on the matter, but I can repeat what the experts are teaching. :D

For anyone that hasn't been out to their seminar I highly recommend it. It's highly educational and a lot of fun.

Best regards,
 
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