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EGT Response During Ignition System Check Question

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HomeBuilt101

Well-Known Member
Joined
Oct 20, 2015
Messages
384
Location
Aguila AZ
As you can tell it is a busy day running back and forth from the engine to the computer...repeat.

I am knocking out a number of items on the Olde Squawk List...another issue I am running is trying to find a bad spark plug or ignition coil.

QUESTION: When you turn off the GOOD ignition system and the engine running rough on the BAD ignition system...does the EGT in the poor running cylinder go up or down?

One (me) would think that if the spark plugs are not firing that well then there is a less hot fire and that would certainly be true in the cylinder itself however...

Since the EGT probe is 2 inches away from the valve during a poor/misfire the not completely burning gas would find its way farther down the exhaust pipe and indicate a hotter EGT...YES??? NO???

Specifically I have a 6 banger with dual Lightspeed Plasma III ignition systems and as designed one coil pack fires the opposing cylinders. When doing a "mag" check I turn off the IGN B the engine runs super smooth and of course following the procedure I turn IGN B back on and then when I turn off IGN A as the engine is running only on IGN B it runs very rough.

I was hoping to see one cylinder go cold and that would indicate a bad spark plug or wire(or wire connection) or if two opposing cylinders went cold that would indicate a bad coil pack or power wire to that coil pack...however his is what I get

..........EGT......EGT WITH......CHANGE
..........BOTH....IGN A OFF......IN EGT

#1 ......1180 .....1220 ...........+40
#2 ......1088 .....1106 ...........+18

#3 ......216 .......172 ............-44 Yes EGT #3 indicates cold today however CHT is normal
#4 .....1142 ......1180 ............+38

#5 .....1195 ......1190 .............-05
#6 .....1130 ......1160 .............+30

So my almost new EGT probe failed...great... !?!?WTF!?!? (Why The Failure!?!?!)

If all of the cylinders reacted in the same way (all getting hotter or all getting cooler) I could assume that the ignition timing/ vacuum advance/ power supply / or ignition module of IGN B was the problem...however not all of the cylinders reacted the same...some went up and some went down.

So whilst I drop a bunch of F Bombs while changing out the almost new EGT probe...can someone PLEASE provide some guidance as to where to look at my ignition system??? Yes...another $100.00 stack of pancakes is available at the next fly in...trailer in for me I guess

: ( + F F F Bombs = me

THANKS!!!
 
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