What's going on here?

[Jay Honeck]

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"

[Chris]

"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?

I would guess you have a bad plug. Something similar happened to me when
landing at Everglades City in Fl.

Putting on some power to turn and back track, the engine started running
rough. I went through the leaning process on the ramp and found the problem
went away when running on only one set of mags.

As it was a rental plane, an engineer came down from Naples and in 5 mins
determined that it was a bad plug just using that chalk that changes colour
when it gets hot.
He isolated the problem, changed the plug and the problem disappeared.

Mind you flying the plane back to Naples had me listening out for every
single sound.

Glad I managed to spot the landing and not need to go around.

Chris

[Matt Whiting]

Jay Honeck wrote:

> 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?

I'm guessing your airplane is female and just doesn't like your wife
being PIC. :-)


Matt

[tony roberts]

Hi Jay

High EGT an low CHT one cylinder:

Fouled plug,
Burned valve,
Broken ring,
Bad mag wire

That's according to the trouble shooting guidwe for my EI engine
analyzer.

HTH

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

[john smith]

What Tony said.
Have you downloaded the data yet?

[John Clonts]

"tony roberts" > wrote in message news:nospam-ABD905.16523021112004@shawnews...
> Hi Jay
>
> High EGT an low CHT one cylinder:
>
> Fouled plug,
> Burned valve,
> Broken ring,
> Bad mag wire
>
> That's according to the trouble shooting guidwe for my EI engine
> analyzer.
>

Not likely to be the valve or the ring since it performed differently on one mag than the other. I would
suggest swapping the plugs and noting whether the problem moved to the other mag or not. Testing the wires is
an easy quick test with an HV tester...when I recently had a similar problem it turned out to be a spark plug
wire.


Cheers,
John Clonts
Temple, Texas
N7NZ

[Almarz]

Okay, after looking at all the replies, you need to stop and analyze
the info given to you on the instrument. If there was a bad plug,
when he switched mags, (he should have leaned it out), the temps would
drop because there was no fire. Same with any other ignition part.
If there was no fuel getting to the chamber, same thing. What you're
seeing is a bad valve, probably exhaust.

Go do another run up and on each mag lean the **** out of it until
it's just about running smooth as it can be with the **** leaned out
of it, then watch the engine instrument. If the temps drop out of a
certain cylinder on a certain mag, you have a plug (or ignition)
problem. That'll be the first test. If that doesn't happen, take her
back and check compression on the cylinder.

Keep us posted.

On Sun, 21 Nov 2004 23:40:56 GMT, "Jay Honeck"
> wrote:

>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]

> Okay, after looking at all the replies, you need to stop and analyze
> the info given to you on the instrument. If there was a bad plug,
> when he switched mags, (he should have leaned it out), the temps would
> drop because there was no fire. Same with any other ignition part.
> If there was no fuel getting to the chamber, same thing. What you're
> seeing is a bad valve, probably exhaust.

How could a bad valve on #2 work okay on "both" mags -- but not on the left
mag?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Dude]

With apologees for hijacking...

I have the opposite problem, high CHT with normal EGT. Strangely enough,
its also my #2 cylinder. I was thinking it was a fuel injection problem.

[John Clonts]

"Dude" > wrote in message ...
> With apologees for hijacking...
>
> I have the opposite problem, high CHT with normal EGT. Strangely enough, its also my #2 cylinder. I was
> thinking it was a fuel injection problem.
>
>

The problem I had with a spark plug wire a couple' months ago was on my # 2 cylinder also!

[Aaron Coolidge]

Jay Honeck > wrote:
:> Okay, after looking at all the replies, you need to stop and analyze
:> the info given to you on the instrument. If there was a bad plug,
:> when he switched mags, (he should have leaned it out), the temps would
:> drop because there was no fire. Same with any other ignition part.
:> If there was no fuel getting to the chamber, same thing. What you're
:> seeing is a bad valve, probably exhaust.

: How could a bad valve on #2 work okay on "both" mags -- but not on the left
: mag?

It can't, you've got a bad plug or wire. Pull the plug and clean it. Spray
the oily plug wires with contact cleaner and clean the inside of the plug
where the wire goes. Put on silicone rocker cover gaskets to prevent future
oil leaks.
--
Aaron Coolidge

[John Galban]

"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:
>
<snip>

Your tests have pretty well narrowed it down to a plug that isn't
firing (the 1st thing I look for when EGT shoots up on one cyl.).
It's unlikely that the mag is firing well on all but one cyl. The
most likely causes are a plug wire or the plug itself. If your mech
is equipped with good testing gear, he should be able to isolate the
problem pretty quickly.

John Galban=====>N4BQ (PA28-180)

[[email protected]]

Bad ignition lead? Excessive plug gap? Bad plug? Flashover inside
the mag?

Somehow you have a marginal ignition situation on that one plug.
These things aren't supposed to happen with autogas.

Post us with what you find. THX

[John Galban]

"Jay Honeck" > wrote in message news:<Mplod.135318$R05.23672@attbi_s53>...
> > Okay, after looking at all the replies, you need to stop and analyze
> > the info given to you on the instrument. If there was a bad plug,
> > when he switched mags, (he should have leaned it out), the temps would
> > drop because there was no fire. Same with any other ignition part.
> > If there was no fuel getting to the chamber, same thing. What you're
> > seeing is a bad valve, probably exhaust.
>
> How could a bad valve on #2 work okay on "both" mags -- but not on the left
> mag?

I think there's some confusion about your troubleshooting. In the
original post, I (possibly by mistake) assumed that when you switched
to the rough mag, the #2 EGT "shot off the scale" to the low end (i.e.
cold). If you're saying it shot off the high end of the scale, this
would not be the kind of reading you'd expect from a cylinder that is
not firing.

On the other hand, like you, I have a hard time imagining how a
stuck valve would behave differently by switching the mags. If an
exhaust valve is stuck open, your EGT should shoot upward off the
scale, but it shouldn't go back to normal by switching mags.

If the symptom is truly that the #2 EGT shoots up when switching to
the rough mag, then something isn't adding up.

John Galban=====>N4BQ (PA28-180)

[Almarz]

It won't. What I'm saying is that if a plug doesn't drop out when
leaned on one mag, that's not your problem. Look elsewhere.

On Mon, 22 Nov 2004 13:00:28 GMT, "Jay Honeck"
> wrote:

>> Okay, after looking at all the replies, you need to stop and analyze
>> the info given to you on the instrument. If there was a bad plug,
>> when he switched mags, (he should have leaned it out), the temps would
>> drop because there was no fire. Same with any other ignition part.
>> If there was no fuel getting to the chamber, same thing. What you're
>> seeing is a bad valve, probably exhaust.
>
>How could a bad valve on #2 work okay on "both" mags -- but not on the left
>mag?

[Almarz]

No fuel, no fire. No fire, no big temps.

On Mon, 22 Nov 2004 15:58:22 GMT, "Dude" > wrote:

>With apologees for hijacking...
>
>I have the opposite problem, high CHT with normal EGT. Strangely enough,
>its also my #2 cylinder. I was thinking it was a fuel injection problem.
>

[Andrew Rowley]

(John Galban) wrote:

> I think there's some confusion about your troubleshooting. In the
>original post, I (possibly by mistake) assumed that when you switched
>to the rough mag, the #2 EGT "shot off the scale" to the low end (i.e.
>cold). If you're saying it shot off the high end of the scale, this
>would not be the kind of reading you'd expect from a cylinder that is
>not firing.

A weak spark rather than no spark maybe? If it's firing but less
efficiently?
My understanding is that this effect also causes EGTs go up when
running on only one mag.

[Matt Whiting]

Andrew Rowley wrote:

> (John Galban) wrote:
>
>
>> I think there's some confusion about your troubleshooting. In the
>>original post, I (possibly by mistake) assumed that when you switched
>>to the rough mag, the #2 EGT "shot off the scale" to the low end (i.e.
>>cold). If you're saying it shot off the high end of the scale, this
>>would not be the kind of reading you'd expect from a cylinder that is
>>not firing.
>
>
> A weak spark rather than no spark maybe? If it's firing but less
> efficiently?
> My understanding is that this effect also causes EGTs go up when
> running on only one mag.

I believe this is possible due to the fact that having both sparks
allows the mixture to burn more quickly and thoroughly prior to opening
of the exhaust valve. If the valve opens while the mixture is only
partially combusted, a jet of flame will exit the exhaust port. This
can greatly increase the EGT, while at the same time lowering the CHT as
the same amount of heat is produced from the charge, but more of it is
going out the exhaust pipe rather than being used to perform work in the
cylinder.


Matt

[Daniel Gram]

A dropped spark plug can crack the insulator enough to be almost
undetectable to the eye but can misfire under compression, making it hard to
find otherwise.
Dan

"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]

> I believe this is possible due to the fact that having both sparks allows
> the mixture to burn more quickly and thoroughly prior to opening of the
> exhaust valve. If the valve opens while the mixture is only partially
> combusted, a jet of flame will exit the exhaust port. This can greatly
> increase the EGT, while at the same time lowering the CHT as the same
> amount of heat is produced from the charge, but more of it is going out
> the exhaust pipe rather than being used to perform work in the cylinder.

Thanks, Matt -- I believe that's exactly what was happening when the EGTs
went off the scale (hotter), and the CHTs dropped down into the 200s.

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.

Thanks to all who chipped in -- man, that EDM-700 is an awesome
trouble-shooting tool.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[#1ACGuy]

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"
>
>

[Ron Natalie]

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.

[TripFarmer]

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

[[email protected]]

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

[Mike Rapoport]

"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

[Jay Honeck]

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"

[Dave Butler]

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