IO-360 A3B6 cyl #1 EGT

[bradp]

These are always fun.  I recently had a plug die (mid flight thank you Champion) in Cyl #1 and replaced the 4 bottoms with Tempest fine wires.  That fixed the spark plug problem, but I'm not quite done yet.  Yesterday I downloaded flights to a USB stick as I was updating the firmware in the EDM-730.    During my most recent trip, I noticed that Cyl #1 wasn't dropping off with the others and the EGT was a bit higher than everyone else.  I uploaded the flight to Saavy and noted the following.

 

1- #1 EGT peaks last - richest cylinder

2- #1 EGT peaks higher than everyone else, EGT spread LOP is ~ 70F

3- Gami spread is ~0.2 GPH

4- LOP CHT #2/3 similar, CHT #4 in the middle, CHT #1 hottest

 

 

Anyone willing to take a stab at this? 

 

Seems like conclusion is  Cyl #1 is running rich and peaking later than everyone else.   Possibilities I can think of (with my limited experience are:  1) (fuel divider?) or 2) everyone else is running too lean (unlikely to be induction leak for 3 cyls - had Cyc #2&4 intake gaskets replaced at last annual as they were leaking.  I last did a baby bottle test over the summer and each was equal.  Will check again.  Something glommed into the divider might make the other 3 cyls leaner but again, occams razor would suggest otherwise, 3) inefficient spark/slower flame front for cyl #1 would result in a hotter EGT.  I already had one champion go out.  Recently tested leads from mag and resistances are in check, so that's less likely.  A mag timing issue would likely affect more than a single Cyl.  4) other ???.  Something about the variability in the FF is bothering me...  something else is telling me to check into my mag leads again.  Trying to be somewhat parsimonious, thus asking our group here...

 

Other things to note:  this is a 4 sec sampling rate = not ideal.  FF has some variability.  ? Transducer / measurement.  However, when the FF smooths out, the EGT wobble / variability goes away.   Reference 00:24. 

 

Lesson learned - there is a TON more information you get with graphical exploration of engine monitoring trends than you do by looking distractedly at the engine monitor in real time during a flight. 

 

What do you guys think? 

 

Thanks as always, 

 

-Brad

 

 

[INA201]

I recently went through somewhat of a similar problem that resulted in a rebuilt fuel divider(original 1978) ", new nozzles, and all new tempests(not fine wire). We pattern tested the nozzles and found that they were shot along with the bottle test showing about half the rate of fuel going to cylinder #2 as the rest.  The low flow to #2 apparently allowed an increased flow to the other 3 cylinders. My guess is the spark is probably ok but easy to check anyway.  Someone smarter than me can chime in on the divider but it works and allows flow at different rates at full throttle vs idle/run up and is wide open during cruise settings.  It needs to be tested imop at low flow and high flow to see if it is functioning properly but please get a second opinion on this vs mine.

Take a look at the thread on this issue.  Like always great responses and support from the MS community.  

 

[smccray]

Have you run a LOP mag check?  I'm betting on an ignition issue. I had a mag die in flight after chasing a couple ignition problems.  I IRAN'd the mags and still had problems. The leads tested okay but the A&P said he thought it was the leads. I took a flyer and replaced them....issue solved.

Not sure about this- is it worth it to run a gami lean test running on one mag?

[bradp]

I did in fact run a mag check LOP in flight and it checked out okay - when my previous spark plug announced that it had quit was on an LOP mag check.  The problem with the spark plug was not nearly as apparent ROP as compared to LOP.   

 

However, my spark plug leads shielding is especially chaffed to Cyl #1 as compared to other cyls, which makes me suspect an ignition problem. 

 

The mags are ~50 since overhaul last July (and I had a big mag problem which prompted me to swap out the previous slick mag for the one that is currently installed).  No other indications of a mag issue.  Starts have thankfully become a non issue with this new mag.  I'll check the timing, but I wouldn't necessarily suspect a mag issue for a single Cyl unless a cap or lead.  I'm leaning... Hehe geddit... Toward a mag lead or another spark plug issue since the involved Cyl is acting too rich (I still have the top plugs as Champion massives).  If acting too lean I'd be suspecting things like induction leaks, valves and lift clearance / camshaft issues.   If acting too rich I'd suspect ignition first and foremost and fuel metering a distant second.   Just an interested, curious PPL / diagnostician by trade, not and A&P though.   

-B

[BDPetersen]

My experience running LOP IO-470's is that a weak spark plug will manifest itself when LOP.  I don't get to enjoy that realm with my O-360.