One high EGT... what next

I have one EGT that is ~150-200 degrees hotter than all others. Understand it's not the exact temp that matters but in this case I believe it's indicative of an opportunity.

CHT's, oil temp, oil pressure ... great.

New Lycoming IO540.... about 25 hours
RV10. Pretty much stock built.
Mags with G3I. I don't think it seems to matter whether G3I is on or not but can't specifically state that I tried this in an extreme lean situation.

what I've done and kind of in order

Switched probes... yep it's the number 2 cly
Cleaned & rotated plugs... not the plugs. wasn't expecting it to be but start simple
Pulled and Cleaned the Injector on #2. no joy
Pulled and cleaned fitting in spider and blew through feeder line between #2 and spider.... no joy

I pulled some data from the AFS this morning... running around 2350 squared.... #2 seems to peak at around 14.3 gph while the remainder start peaking around 12.3. Engine definitely runs rough when getting to the level that the remainder of the cylinders are peaking.

At normal cruise... running rich, engine seems to run fine and smooth but the EGT is still hot on #2 compared to the remainder of the cylinders.

I've read to check for induction leaks but haven't chased down what that really means or how to? I'll pull my Sky Ranch book out shortly

Next step for me....
I'll probably switch the injector in #2 for one of the other cylinders just to see if it follows the injector...

I'm about out of ideas.... what do I look for next?

Thanks in advance for any ideas,
Doug

A couple of thoughts.

First, position of the sensors can make quite a difference. For that reason it is better to think of the EGT as a "trend instrument." The only absolute truth is that, for a given volume of fuel and a given volume of air in identical cylinders with identical plugs and spark, the burn temperature will be about the same.

Second, you are noticing that that cylinder peaks early. That is indeed a good time to identify the cylinder that peaks last and swap the injectors. If that reverses the leaning peak order, then you may need to start playing with different injectors or techniques to hone the smaller holed injector larger. Sometimes reversing them does not change the order of peak - that could be due to a slightly different pressure in one injector line, and thus the one with higher pressure might need a slightly smaller injector.

That's as much as I know, there's lots smarter folks than me out there. I understand that balancing flow can be an arcane art...

Some things to try...

Most likely one of 3 things:

1) Low fuel flow - check by running hoses from nozzle lines to containers and see if #2 flows the same as some of the others.

2) Induction Leak - I check by spraying carb cleaner or some other highly volitile spray around the induction tubes with the eng running (RPM will rise if you find a leak). Wear goggles.

3) One plug is not firing - check when flying by switching off mags to see of they both "drop" the same or if one is much rougher than the other.

Try this: Don't just switch probes, but trade probes so that #2 reads on #4. Tells you if you have wire weirdness somewhere. Check the induction tube hose clamps. I have seen the gasket on the intake port out of place more than once. Make sure the intake tube isn't cocked in the tube flange recess. Sometimes they get out during torquing. Only takes a couple minutes to drop that flange & check gasket/tube fit.

EGT is not a static temp reading!

EGT is the temp of the probe and nothing else. The number is of very little importance. What is important is the CHT which you say is OK. In addition the EGT is influenced by such things as the size of the probe, its location, if it is grounded or ungrounded, the cam lifter profile and a variety of other things.

Unlike high CHT, High EGT is not an indicator of harm happening to the engine. High Compression and advanced timing cause the EGT to go down yet increase stress to the engine. You can raise the EGT by retarding the timing and lowering the compression both do not harm the engine. So ?high? EGT is not an indicator of harm happening to the engine.

Thinking that high EGTs are bad is not an accurate thought just as having all the EGTs being equal is "good" is not an accurate thought. They are relative values and can be used in determining the GAMI spread.

So what you are looking for is a small "GAMI spread" which I will let you research. Basically it is the difference in the fuel flow values as each cylinder reached peak EGT. The GMI Spread determines the need to balance the injectors if there is a need to balance them.

My small knowledge of this is from my belief that Mike Busch of Savvy Aviator fame knows what he is talking about. For CPA members there is an excellent article in the March issue of the CPA magazine on this very topic.

Today one of my cylinders (#3) EGT took off at about 200 hotter than the rest. I know there is discussion about what is an acceptable peak, but just wondering if anyone sees similar phenomenon.

Taxi, run up and initial takeoff all EGT's about 1280, CHTS 350-400. After about 15 seconds #3 shot up to 1460. CHT normal 380. #3 is usually the coolest cylinder CHT wise. Once I leveled off and set up for cruise the temps were all balanced and #3 wasn't the hottest at 50% power. At 65% #3 is about 80 or so higher than the rest.

I decowled, checked the intake tubes and re torqued everything with no change.

I will do a compression test tomorrow to check for valve issues. I am not overly concerned, but its something that just started happening today.

I have an o-320, dual P-Mags, FP. Engine TT is 25 hrs.

Anyone have any thoughts.

Intake leaks on NA engines are only obvious at part throttle operation. If you level off at full or almost full throttle (low restriction) you probably won't see any temp diffs from a leak. The more throttle valve restriction you have, the more an intake leak will present itself.

I'd try two gami tests.

7DeltaLima said:

I have one EGT that is ~150-200 degrees hotter than all others.
#2 seems to peak at around 14.3 gph while the remainder start peaking around 12.3.
I've read to check for induction leaks but haven't chased down what that really means or how to?
Next step for me....
I'll probably switch the injector in #2 for one of the other cylinders just to see if it follows the injector...

Doug

Click to expand...

Isn't it nice having tools for diagnosis? I think you've hit on the problem, #2 is running much leaner than the rest. But is it because of vacuum leak or injection system? I'd suggest doing a gami spread test with the throttle mostly closed, low altitude, maybe 15 inches or whatever it takes for safe flight. The goal here is maximum differential between ambient and induction system pressure- get that leak to leak!. Then do a WOT gami spread and see what you get (go to altitude if that's what you need to do for your personal engine management comfort). If #2 is dramatically lean on both tests, pursue fuel injection fixes, if #2 is dramatically lean on the partial throttle test, not so on the WOT, then it would seem like a vacuum leak is the culprit.