rough engine just after power reduction

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

Sydney Hoeltzli <last_name@swbell.net> wrote in message news:<3F2138E0.6060600@swbell.net>...
<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

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

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

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

G.R. Patterson III wrote:

> 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,

How would you check the wiring harness?

As of today, Tigger was running like a Tiger and purring like
a kitten.

EGTs were lower on ground run too.

So we'll hope it was bad plugs, but my "we haven't gotten to
the bottom of this" warning is still beeping in the back of my
head.

Cheers,
Sydney

Sydney Hoeltzli wrote:
>
> How would you check the wiring harness?

Unfortunately, I don't know. My A&P did that when I had my problem.

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