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recapen(at)earthlink.net Guest
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Posted: Mon Dec 03, 2012 2:34 pm Post subject: Engine combustion troubleshooting concepts |
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Re-breaking in my engine after prop-strike by hangar door induced by tornado.
Considering the engine already had 160+ hours on it - I know how it was running for a while.
I have one cylinder running not like the others. Before I tell what is happening, I want to make sure I understand/remember the basic concepts.
EGT-only elevated - CHT reduced...unburned fuel going out exhaust and burning on the way out - plug not firing
EGT-only elevated - ...unburned fuel going out exhaust and burning on the way out - plug not firing completely
CHT-only elevated...not enough cooling air
EGT and CHT elevated...lean mixture - air leak
Refresh my memory here.
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Shannon Miller
Joined: 12 Jan 2008 Posts: 3
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Posted: Mon Dec 03, 2012 4:22 pm Post subject: Engine combustion troubleshooting concepts |
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I'm no expert, but I can share my own understanding. See below.
On Mon, Dec 3, 2012 at 2:33 PM, Ralph E. Capen <recapen(at)earthlink.net (recapen(at)earthlink.net)> wrote:
Quote: | Re-breaking in my engine after prop-strike by hangar door induced by tornado.
Considering the engine already had 160+ hours on it - I know how it was running for a while.
I have one cylinder running not like the others. �Before I tell what is happening, I want to make sure I understand/remember the basic concepts.
EGT-only elevated - CHT reduced...unburned fuel going out exhaust and burning on the way out - plug not firing
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Right. Possibly some sort of spark plug problem. Could be a fouled plug or disconnected/broken plug wire. Consider a mag check (even if you're only seeing this in flight -- just do it at a safe altitude and within gliding distance to a safe landing spot) to identify the plug/wire; if the engine quits, pull the throttle to idle before switching off the bad mag to avoid backfiring.
�
Quote: | EGT-only elevated - ...unburned fuel going out exhaust and burning on the way out - plug not firing completely
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Agreed. Same possible causes as above.
�
Quote: | CHT-only elevated...not enough cooling air
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Or insufficient fuel flow, power too high for the air flow, mixture too lean, or RPM too low for the power setting. Possible in-flight solutions: lower nose to increase airspeed, open cowl flaps if you have them, enrichen the mixture (confirm that you're rich of peak by noting a decrease in EGT's as you enrichen the mixture), reduce power (MP), increase prop RPM. Now if it's just one cylinder, I would guess it's either some sort of baffling issue or fuel flow issue to that cylinder.
�
Quote: | EGT and CHT elevated...lean mixture - air leak
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Agree, or possible magneto/ignition problem if it's all cylinders -- a mag check would identify which mag/ignition source. If it's just one cylinder, it could be a partially clogged fuel injector: go full rich mixture and momentarily turn on the boost pump -- it might dislodge the clog!
Quote: |
Refresh my memory here. |
I assume you're talking only "somewhat" elevated EGT and CHT values, and not values which are "sky high" which could indicate detonation or pre-ignition and ultimate�catastrophic�engine failure!
That's all I can offer. No warranty, but I hope it helps!
--Shannon
[quote][b]
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recapen(at)earthlink.net Guest
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Posted: Tue Dec 04, 2012 4:48 am Post subject: Engine combustion troubleshooting concepts |
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Thanks.
This was only one cylinder, the EGT only went up (enough to catch my attention - not red-line).
I have already pulled both plugs - the lower one was wet which may not mean anything. Neither of them looked abnormal - cleaned and reinstalled.
--
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Kellym
Joined: 10 Jan 2006 Posts: 1705 Location: Sun Lakes AZ
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Posted: Tue Dec 04, 2012 6:11 am Post subject: Engine combustion troubleshooting concepts |
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Only two items will cause a single cylinder EGT to rise significantly.
Either one plug stopped firing, or an induction leak developed. Single
spark instead of two plugs firing will cause 50-150 degree EGT rise. So
will a loose intake tube or gasket.
On 12/4/2012 5:47 AM, Ralph E. Capen wrote:
[quote]
Thanks.
This was only one cylinder, the EGT only went up (enough to catch my attention - not red-line).
I have already pulled both plugs - the lower one was wet which may not mean anything. Neither of them looked abnormal - cleaned and reinstalled.
--
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_________________ Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
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recapen(at)earthlink.net Guest
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Posted: Tue Dec 04, 2012 6:25 am Post subject: Engine combustion troubleshooting concepts |
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Thanks - I'll keep looking for an induction leak.
Already contemplating moving my MAP sensor port from that cylinder to the one in front of it.
--
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