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#1
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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 |
#2
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"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. |
#3
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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 |
#4
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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/ |
#5
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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 |
#6
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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 |
#7
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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 |
#8
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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 |
#9
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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 |
#10
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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 |
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