What's going on here?

Bad plug. Lead fouling isn't the only reason they go bad. If it was a wire,
agressive leaning wouldn't have done anything.
Alex
"Jay Honeck" wrote in message
news:cI9od.66570$V41.11973@attbi_s52...
Our JPI EDM-700 engine analyzer may have paid for itself today.

Here's the scenario:

Mary is PIC. During her run-up, the left mag dropped a bit more than the
right. She leaned it back (the usual fouled-plug procedure) and it
smoothed
out to within specs. Still not as smooth at the right, but with less than
a
75 rpm drop.

Climb out was normal, with that O-540 pulling like a tractor at over 1000
feet per minute. Life was good, especially after surviving the
Wisconsin-versus-Iowa Big Ten football game...

Upon leveling out, and getting everything cleaned up, I was messing around
with our new CO detector, which is mounted on the pilot's-side at elbow
height. (Recommendation: Don't reach across your pilot like this unless
you're married to her! :-)

As I was tinkering with it, my eyes were drawn to the EDM-700, which was
clearly showing something amiss with the #2 cylinder. EGT was over 1630
degrees (we try to keep them under 1500), and the CHT was way low -- like
in
the low 200s.

We tried leaning, and enrichening, and different throttle settings, but
that
cylinder stayed way out of line with all the others. Strangely, nothing
sounded amiss at all, and the engine seemed to be performing normally.

I was about to suspect something wrong with the JPI, when I suggested that
we try switching to one mag, then the other, in flight. On the right mag,
all was well -- but on the left mag, the engine started shaking, and the
#2
EGT shot off the scale!

Switching back to "both" everything smoothed out. In fact, we still could
not detect anything amiss "by ear" -- but the #2 cylinder was still "out
of
whack" with the others.

Since we were closer to our destination than home, we elected to continue
on
and land. On the ramp Mary did a run-up, and the #2 cylinder was still
clearly not firing on the left mag. We then ran it up on "both", and
leaned
it severely -- again, the usual procedure for a fouled plug.

After this it was better, but not perfect -- so we de-cowled the engine,
and
checked everything thoroughly. Other than the #2 cylinder's bottom spark
plug wire being oily (actually, all the bottom wires are), I couldn't find
anything amiss. I wiggled all the wires, made sure they were not bent
over
too sharply, checked all connections at the mags -- and then went to
dinner.

Of course, this bothered me throughout dinner, and I really couldn't enjoy
myself.

On the return flight, with me acting as PIC, I did a VERY thorough run-up,
with a long, brutally leaned 2000 RPM test. Everything tested and ran
fine -- and remained fine all the way home, at all throttle, prop and
mixture settings.

What's going on here? We burn unleaded car gas, so it seems unlikely
that
we had a lead-fouled spark plug (we haven't bought avgas in several
weeks) -- could it be a bad plug? Or a bad spark plug wire?

Can a mag fail in such a way as to only hinder a single spark plug from
firing?

I'm going to call my A&P tomorrow to have him check it over, but anyone
got
any ideas?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:

I didn't have time to work on the plane today, but I'm gonna yank that plug
and have my mechanic test it in his brand new spark plug tester -- the kind
that actually pressurizes (or does it lower the pressure?) it while testing.

Increases...no matter what the ambient pressure in, the cylinder is many
times that inside.

Now if you're testing the ignition leads....

Of course you could bite the bullet and spend the $25 on a new plug.

Jay,

Hope you find out what it is. Let me know if you do so I can learn from you.

BTW, I was getting 1,400fpm on the new cylinders last week........I couldn't
believe it.


Trip

On Tue, 23 Nov 2004 04:30:36 GMT, "Jay Honeck"
wrote:

snip

I didn't have time to work on the plane today, but I'm gonna yank that plug
and have my mechanic test it in his brand new spark plug tester -- the kind
that actually pressurizes (or does it lower the pressure?) it while testing.

If that's not it, I'm betting on the wiring harness.

Swap all the plugs top-to-bottom. If it is a bad spark plug (which may
pass the bomb test just fine) the next time the problem rears it's
head it will be on the other magneto.

If your local guy has a high-tension lead tester, testing the leads is
simple and fast. You could check just the one with the "issue", or
when swapping the plugs top-to-bottom, you could check them all.

As someone else indicated, oil on the lower plug wires is a bad thing,
and not what I would consider to be typical (or acceptable).

I'm curious, what type of mags are installed? How much time is on the
engine/mags since you bought the airplane/had the engine major'd?

TC

"Jay Honeck" wrote in message
news:cI9od.66570$V41.11973@attbi_s52...
Our JPI EDM-700 engine analyzer may have paid for itself today.

Try exchanging the upper and lower plugs on the #2 cylinder and see if the
problem switches to the other mag. Don't clean or do anything to the plugs
or harness, the first priority is to identify the problem. It has to be in
the ignition system.

Mike
MU-2
Helio Courier

A couple of days ago I posted about a problem with my #2 cylinder. Watching
my JPI EDM-700 in flight, the EGTs on #2 shot to over 1600 degrees, and the
CHT sank to 200 degrees. After trouble-shooting, it became apparent that the
condition became much worse when set on the left mag only.

In other words, the #2 cylinder was not firing -- or, at least, not firing
consistently -- when on the left mag. On "both", the only symptom was the
bar graph on the EDM -- the engine sounded perfectly normal.

Yesterday I removed BOTH spark plugs from the #2 cylinder (I figured "why
not?" as long as I was at it) and had my A&P test them in his pressurized
spark plug tester. Both were clean, and checked out fine.

He re-gapped them, and I reinstalled them. They were off, according to my
A&P, so I believe my next step will be to re-gap ALL the spark plugs.

I also sprayed the oil-saturated wiring harness down with contact cleaner,
which did a fine job of "de-greasing" them.

All connections appeared fine, although I didn't take the mag connections
off. I figure I'll take her around the patch when I get time, to see if all
is now well. (It WAS well on our way home, if you recall, after leaning
severely during a long run-up.)

My mechanic said what I did MAY fix it, if it was just a chunk of crud on
the spark plug causing it to mis-fire. But he also said it could be a bad
lead wire, or a bad distributor inside the mag.

Thanks to all who have responded -- is there anything else to check? I
find it hard to believe that I could have had a fouled plug, given the fact
that we usually burn unleaded mogas, but perhaps it's a plug that only fails
when hot?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:

He re-gapped them, and I reinstalled them. They were off, according to my
A&P, so I believe my next step will be to re-gap ALL the spark plugs.

disclaimer: I'm no mechanic, but I've cleaned and gapped a few spark plugs in my
life, both automotive and aircraft.

It's possible you just got a piece-o-junk in the gap and it was dislodged when
the plug was removed, and it will be just fine forever onward.

You could also have an invisible crack in the insulator that only shows up when
hot or under combustion chamber pressure, in which case the problem will reappear.

Some people intentionally make the gap wider than spec, particularly on a plug
that has a tendency to foul.

My understanding of the rationale is that the wider gap gives a more reliable
spark, but causes higher voltages in the high tension wiring, which might cause
other symptons, like crossfiring. Apparently you can routinely get away with a
gap that's wider than spec.

Dave