My EGT's have risen 100 degrees!!

pierre smith · #1 12-29-2010, 02:57 PM

...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,

Sig600 · #2 12-29-2010, 03:12 PM

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.

sjarrell · #3 12-29-2010, 03:45 PM

What are your CHTs? Did they go up as well or are they normal?

AlexPeterson · #4 12-29-2010, 04:07 PM

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.

asav8tor · #5 12-29-2010, 04:54 PM

Quote:

Originally Posted by AlexPeterson

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.

BINGO!!!!
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airguy · #6 12-29-2010, 07:24 PM

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?

aerhed · #7 12-29-2010, 08:23 PM

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?

NDrv8r · #8 12-29-2010, 08:34 PM

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

pierre smith · #9 12-30-2010, 05:34 AM

...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,

AlexPeterson · #10 12-30-2010, 08:01 AM

Quote:

Originally Posted by pierre smith

...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 - 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.