rough engine just after power reduction

Last night, on a short hop back to home base after an
instrument lesson (read: extended low power ops),
engine shuddered and ran very rough just after level-off
and power reduction. Run-up and takeoff were normal,
and as usual I leaned like heck for taxi and during
runup. About 80 degrees with blissfully low humidity,
carb ice unlikely esp. in our installation, not very
carb ice prone.

Ground ran with brutal leaning afterwards and checked
all chts/egts on both, r and l mag. r mag ran rougher,
with higher EGT on #4 cyl.

Suggestions? Going out to clean plugs and make sure
all 4 cyl have compression this afternoon, what else
to check? I'm hoping for a badly fouled plug, but
would that produce high EGT on 1 mag?

BTW I envy the chap in the other thread who posted about
"continuing as normal as possible" because an engine w/
a blown valve will continue to make normal power for
a long time. Personally when my engine is running rough
I'm not capable of such savoire-faire, I operate on the
assumption that I really don't know what's up and the
b**ch may quit on me any second. I want as much energy
as I can bank until I have the runway made.

Cheers,
Sydney

"Sydney Hoeltzli" wrote in message
...
Last night, on a short hop back to home base after an
instrument lesson (read: extended low power ops),
engine shuddered and ran very rough just after level-off
and power reduction. Run-up and takeoff were normal,
and as usual I leaned like heck for taxi and during
runup. About 80 degrees with blissfully low humidity,
carb ice unlikely esp. in our installation, not very
carb ice prone.

Ground ran with brutal leaning afterwards and checked
all chts/egts on both, r and l mag. r mag ran rougher,
with higher EGT on #4 cyl.

Suggestions? Going out to clean plugs and make sure
all 4 cyl have compression this afternoon, what else
to check? I'm hoping for a badly fouled plug, but
would that produce high EGT on 1 mag?

BTW I envy the chap in the other thread who posted about
"continuing as normal as possible" because an engine w/
a blown valve will continue to make normal power for
a long time. Personally when my engine is running rough
I'm not capable of such savoire-faire, I operate on the
assumption that I really don't know what's up and the
b**ch may quit on me any second. I want as much energy
as I can bank until I have the runway made.

Cheers,
Sydney


Hi Sydney
I've had two rough engine scenarios in flight.
Once in '69 in a Cardinal and it just cleared up with leaning.
The other time in a Skyhawk; Dropped an exhaust valve and I landed at the
nearest airport.
Both cases carbureted Lycoming 4's.
Never had ice that I noticed.
H.
N502TB

Oh yes, my Baron is still sitting there.
Seven weeks.

Sydney Hoeltzli wrote:

Last night, on a short hop back to home base after an
instrument lesson (read: extended low power ops),
engine shuddered and ran very rough just after level-off
and power reduction.

Wow, this is the first time I've heard an actual first-hand account of
the engine running rough after the initial power reduction.

Good job handling it, Sydney.


Ground ran with brutal leaning afterwards and checked
all chts/egts on both, r and l mag. r mag ran rougher,
with higher EGT on #4 cyl.

Suggestions? Going out to clean plugs and make sure
all 4 cyl have compression this afternoon, what else
to check? I'm hoping for a badly fouled plug, but
would that produce high EGT on 1 mag?

Fouled spark plug, faulty spark plug, bad lead, bad distributor... all
possibilities.

Was there any drop in CHT on cyl. #4? If so, it could be a burned
exhaust valve.

Let's hope it wasn't anything expensive.

-Ryan
CFII-A/MEI/CFI-H

In article ,
Sydney Hoeltzli wrote:
to check? I'm hoping for a badly fouled plug, but
would that produce high EGT on 1 mag?

I'm not an expert, but I understand you can get weird effects if the
combustion is still going on during the exhaust cycle. I thought that
was usually due to a leaking exhaust valve, though.

--
Ben Jackson

http://www.ben.com/

Sydney Hoeltzli wrote in message ...
snip
Ground ran with brutal leaning afterwards and checked
all chts/egts on both, r and l mag. r mag ran rougher,
with higher EGT on #4 cyl.

Suggestions? Going out to clean plugs and make sure
all 4 cyl have compression this afternoon, what else
to check? I'm hoping for a badly fouled plug, but
would that produce high EGT on 1 mag?

Puzzling! It sounds like a bad or fouled plug, but the EGT doesn't
make sense. If you were running on both mags, a bad plug would show
up as a higher EGT on that cylinder. If you switched to the rough
running mag, the EGT for the bad plug should drop. Running on a
single (good) plug causes the EGT to rise since the fuel air mixture
doesn't burn as quickly and is still burning when ejected into the
exhaust. If you're running on a single plug that is firing
intermittently, I'd expect the overall EGT to be lower, since there
are (cold) unburned charges exiting the cylinder.

Could the high EGT reading be coming from unburned charges being
ignited in the exhaust stack by subsequent burning charges?

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


BTW I envy the chap in the other thread who posted about
"continuing as normal as possible" because an engine w/
a blown valve will continue to make normal power for
a long time. Personally when my engine is running rough
I'm not capable of such savoire-faire, I operate on the
assumption that I really don't know what's up and the
b**ch may quit on me any second. I want as much energy
as I can bank until I have the runway made.

Cheers,
Sydney

John Galban wrote:

Puzzling! It sounds like a bad or fouled plug, but the EGT doesn't
make sense. If you were running on both mags, a bad plug would show
up as a higher EGT on that cylinder.

And it was higher, a bit, on a cylinder which usually isn't
the hottest...

If you switched to the rough
running mag, the EGT for the bad plug should drop.

'swhat I would have thought too.

Well, there was a lot of lead fouling in all the bottom plugs
(which were cleaned recently -- ugh!). But nothing that looked
as though it should have put one plug out of commission. Unless
I burnt it off with ground running, I'm suspicious that this
isn't the end of the problem.

Just pulling through the prop, it's clear that #4 cylinder
(the one w/ the high EGT) doesn't have as much compression
as the others. Still got compression though. Dunno how
quantitative. Pulled the rocker box cover, no sign of soot
in the oil (the poor man's "exhaust valve going bad" warning
system). #4 happens to be our only remaining NuChrome cylinder
and had lower compression than I'd like last annual (no leakage
past the valve though, and the wobble check was good)

How does one check the ignition wires for proper function,
and if one plug isn't producing spark as George suggested,
would it be fouled?

Methinks a compression check is in our future. Meworries about
another sort of check.

Meworries more about not tracking down the problem...of course
some people would say I worry too much about 1 minute of rough
running.

Cheers,
Sydney

Sydney,

Why don't you swap the top an bottom plugs, if they both look fine. The
next time it happens, and IF it is on a different mag, then you know for
sure this is a plug gone bad, and you'll know which one. If the same
mag, suspect wiring or a sticky valve. A can of Rislone in the oil can
solve it if it is minor. If not, the valve guide needs a reamer shot
and this is not a minor procedure. Guess you better be sure you are on
the right culprit first.

Just for the record, absolute EGT temperature doesn't mean a thing if
you have not assessed its relationship to peak. An unusual change in
EGT while cruising is a revelating event, but a power setting change
can (and will) change it too (particularely on carburated engine). If
your original comment that EGT#4 read higher, was it a "not the usual
reading I see" or "while it got rough, I saw it change". The first one
is normal (well, you didn't quantify the change, but I assume here it
was minimal), since on a power reduction you don't necessarely see the
same charge distribution across every cylinders (particularely if your
intakes aren't tuned). The other case is more revealing but symptomatic
of either a valve problem or a plug problem (so it just confirms you
that you were not dreaming about the rougness).

Trouble with those intermitents is that they are!

Francois (also get worried when his engine goes rough) Marquis

Sydney Hoeltzli wrote:
John Galban wrote:

Puzzling! It sounds like a bad or fouled plug, but the EGT doesn't
make sense. If you were running on both mags, a bad plug would show
up as a higher EGT on that cylinder.


And it was higher, a bit, on a cylinder which usually isn't
the hottest...

If you switched to the rough
running mag, the EGT for the bad plug should drop.


'swhat I would have thought too.

Well, there was a lot of lead fouling in all the bottom plugs
(which were cleaned recently -- ugh!). But nothing that looked
as though it should have put one plug out of commission. Unless
I burnt it off with ground running, I'm suspicious that this
isn't the end of the problem.

Just pulling through the prop, it's clear that #4 cylinder
(the one w/ the high EGT) doesn't have as much compression
as the others. Still got compression though. Dunno how
quantitative. Pulled the rocker box cover, no sign of soot
in the oil (the poor man's "exhaust valve going bad" warning
system). #4 happens to be our only remaining NuChrome cylinder
and had lower compression than I'd like last annual (no leakage
past the valve though, and the wobble check was good)

How does one check the ignition wires for proper function,
and if one plug isn't producing spark as George suggested,
would it be fouled?

Methinks a compression check is in our future. Meworries about
another sort of check.

Meworries more about not tracking down the problem...of course
some people would say I worry too much about 1 minute of rough
running.

Cheers,
Sydney

Francois Marquis wrote:

Just for the record, absolute EGT temperature doesn't mean a thing if
you have not assessed its relationship to peak.

Of course

An unusual change in
EGT while cruising is a revelating event

I wasn't perusing the EGT in flight. More interested in putting
myself in a position to make the airport.

, but a power setting change
can (and will) change it too (particularely on carburated engine). If
your original comment that EGT#4 read higher, was it a "not the usual
reading I see" or "while it got rough, I saw it change". The first one
is normal (well, you didn't quantify the change, but I assume here it
was minimal)

Actually, no, it was significant. Normally during ground run before
shutdown (I follow the Lycoming SB for plug fouling, ground run at
~mag check rpm while lean), I see EGTs in the 1000s. That day they
were all higher -- closer to cruise EGT of about 1200-1300 with
#4 being 1400 and on R mag 1490.

Peak is about 1500 in my plane.

After cleaning the plugs, ground run EGTs back to normal. Still not
sure why fouled plugs = higher EGTs but I'll take it

Thanks
Sydney

Sydney Hoeltzli wrote:

Suggestions? Going out to clean plugs and make sure
all 4 cyl have compression this afternoon, what else
to check? I'm hoping for a badly fouled plug, but
would that produce high EGT on 1 mag?

It could do that. High EGTs can be produced by a slow fuel burn in that
cylinder, and this can be produced by fouled plugs.

Make sure you check the wiring harness too. Last time I had this sort of
problem, one plug was fouled *because* the other one wasn't firing and
she was running too rich on that cylinder. The other plug wasn't firing
because the plug wire had quit conducting electrons.

George Patterson
The optimist feels that we live in the best of all possible worlds. The
pessimist is afraid that he's correct.
James Branch Cavel

I have Glasair II with I-O360. When training and running low power for
extended periods I get a little roughness. If I run it harder then I don't
get the roughness. It may pop on final or while taxing, my mech said it is
because the plugs get "loaded up". Meaning a little fouling. When my
instructor wants me to stay at 90kts my power settings are very low and the
engine oil heats up to a little over 200F. Other wise it runs 190-195. This
is because airflow and nose high attitude.


Steve