IO550 - Popping at Idle

MyassisDragon

MyassisDragon

Line Up and Wait
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Mr Fred
So I have noticed something that seems to be affected by cold starts in colder weather.

When I start My IO550 (gami injectors) and the engine is cold (around 50-55 degree F ) one of the cylinders sounds like it is popping out the exaust and stumbling at idle or above.

I suspect it is #2 cylinder since the EGT/CHT temp rises on this one first well before the rest.

After the other cylinders come up to temp (160-180CHT) it goes away and the #2 temperature settles down lower to match the rest. Also this is NOT impacted by the mixture regardless how far I lean or enrich. So I am thinking ignition. :dunno:

Any ideas?

But here is where its funny, It never did it in warmer temperatures, or on hot starts or even if I keep it in the hangar above 60 degrees. Only since the temps are getting colder in michigan.

I dont like it since its not just running rough but popping and raising the EGT/CHT right at start. BUT only when its cold and on #2 cylinder....:confused:
 
induction leak.....sounds like it to me.

Check the rubber intake fittings for cracks or loose clamps. You could have your mechanic pressurize and spray down your engine with soapy water and find the leaks.

also....could be a cracked tube....?
 
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I agree with Checkout_my_Six with regard to a rubber fitting somewhere around the chamber.

It could be a hairline crack somewhere, but wouldn't he still get a very minor continuation of the blow-by even at temperature with a metal fracture?
 
Sniffle valve? Not sure if that engine has them but my Lycoming engine has them and mine would stumble and pop at idle.. Removed them and cleaned and never had the problem again.
 
MyassisDragon said:
So I have noticed something that seems to be affected by cold starts in colder weather.

When I start My IO550 (gami injectors) and the engine is cold (around 50-55 degree F ) one of the cylinders sounds like it is popping out the exaust and stumbling at idle or above.

I suspect it is #2 cylinder since the EGT/CHT temp rises on this one first well before the rest.

After the other cylinders come up to temp (160-180CHT) it goes away and the #2 temperature settles down lower to match the rest. Also this is NOT impacted by the mixture regardless how far I lean or enrich. So I am thinking ignition. :dunno:

Any ideas?

But here is where its funny, It never did it in warmer temperatures, or on hot starts or even if I keep it in the hangar above 60 degrees. Only since the temps are getting colder in michigan.

I dont like it since its not just running rough but popping and raising the EGT/CHT right at start. BUT only when its cold and on #2 cylinder....:confused:
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Try leaning, it sounds like the fuel is still burning hard when the exhaust valve is opening, once the engine warms up it will burn the fuel better. You may also have a weak plug in #2.
 
Quick update - #2 lower plug went bad and the resistance was 850,000 ohms. (Should be between 500-5000 ohms)
 
Henning said:
Try leaning, it sounds like the fuel is still burning hard when the exhaust valve is opening, once the engine warms up it will burn the fuel better. You may also have a weak plug in #2.
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Impressive!
 
Installed a full new set of Tempest Fine wires yesterday. (5 out of the 12 champion massive were bad, between 50,000 & 1,300,000 ohms)
There are also no temperature drops with mag drops anymore so there was a spark plug issue also that is fixed now.

But it only made the problem better and not cured, so it wasn't the spark plugs. Also tightened the intake bolts a few days earlier and this also made things better.

So now that I have eliminated weak firing I noticed #1 & #2 cylinder run hotter than normal EGT when the engine is cold (50-55deg f startup and EGT is +350deg f) and they do drop when I aggressively lean. Then when the pop goes away the engine is at a point of stumbling on the other cylinders and the engine runs rough and close to stalling.

So here is what I am wondering. Did anything really change mechanically since I flew the plane home from California?

This plane has always lived in SoCal in a warm dry climate (Ramona) and the problem started when we got back to Michigan and the temperature dropped below 50 (keep hangar at 55). Come to think of it, the first day I had issues was when it was our first cold and windy day in the 50's

So this old girl was never setup or run in cold startups, and the #1&2 cylinders are definitely running rich on startup. These are the two cylinders farthest back towards the firewall on the continental 550. :dunno::dunno::dunno:
 
Morning sickness
Gonna have to have the exhaust valve guide reamed on those two cylinders.
Oh well, they call owning an airplane part of the two happiest days of your life for a reason :yes:

Should be a happy engine by the time you are done.
 
MyassisDragon said:
Installed a full new set of Tempest Fine wires yesterday. (5 out of the 12 champion massive were bad, between 50,000 & 1,300,000 ohms)
There are also no temperature drops with mag drops anymore so there was a spark plug issue also that is fixed now.

But it only made the problem better and not cured, so it wasn't the spark plugs. Also tightened the intake bolts a few days earlier and this also made things better.

So now that I have eliminated weak firing I noticed #1 & #2 cylinder run hotter than normal EGT when the engine is cold (50-55deg f startup and EGT is +350deg f) and they do drop when I aggressively lean. Then when the pop goes away the engine is at a point of stumbling on the other cylinders and the engine runs rough and close to stalling.

So here is what I am wondering. Did anything really change mechanically since I flew the plane home from California?

This plane has always lived in SoCal in a warm dry climate (Ramona) and the problem started when we got back to Michigan and the temperature dropped below 50 (keep hangar at 55). Come to think of it, the first day I had issues was when it was our first cold and windy day in the 50's

So this old girl was never setup or run in cold startups, and the #1&2 cylinders are definitely running rich on startup. These are the two cylinders farthest back towards the firewall on the continental 550. :dunno::dunno::dunno:
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Start by having the injection system recalibrated and set up now that you have plugs that work, as well as make sure all the timing/points gap is correctly set. May as well start at the beginning and get everything to where it's supposed to be, then figure out what is still remaining.
 
Quick update - It was a little warmer yesterday (15-20 deg) and I kept the hangar at 60 deg f. Then warmed the engine up with the cowl flaps closed and the popping is almost gone, its just a slight mis every few seconds where the pop was but went away within a minute. I noticed it will completely go away if I idle at 1050-1100 rpm (aggressive lean) but showed back up at 850-900 rpm.

The engine runs good at LOP cruise with CHTS withn 10 deg and EGT's within 50 deg.
So my plan now is just fly until something changes and stop trying to make it run like a sewing machine.

Regarding #1&2 EGT hotter on startup - I posted on Beechtalk and talked to 2 other local owners of IO550's and the consensus is that this is completely normal and not related to the idle issue I was chasing.
 
The engine has a pretty aggressive camshaft, and with that some popping at low rpm idle is normal.
 
Problem solved and completely fixed now. :yes:

During an oil change I had my AP check "ALL" the intake flange bolts and he found 2 very difficult ones to reach that were loose (#1 &#5 cylinders under and behind the manifold) .

Tightened these up and now she runs pretty smooth at idle, with just a little rhythmic loping at low RPM (700-900rpm) but no stumbling or popping. He thought it sounded gggggreat and typical for a big bore Continental.
 
MyassisDragon said:
Problem solved and completely fixed now. :yes:

During an oil change I had my AP check "ALL" the intake flange bolts and he found 2 very difficult ones to reach that were loose (#1 &#5 cylinders under and behind the manifold) .

Tightened these up and now she runs pretty smooth at idle, with just a little rhythmic loping at low RPM (700-900rpm) but no stumbling or popping. He thought it sounded gggggreat and typical for a big bore Continental.
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For some reason I recall a text I sent you. :D

Good you got it figured out.
 
MyassisDragon said:
Problem solved and completely fixed now. :yes:

During an oil change I had my AP check "ALL" the intake flange bolts and he found 2 very difficult ones to reach that were loose (#1 &#5 cylinders under and behind the manifold) .

Tightened these up and now she runs pretty smooth at idle, with just a little rhythmic loping at low RPM (700-900rpm) but no stumbling or popping. He thought it sounded gggggreat and typical for a big bore Continental.
Click to expand...

Excellent. Yeah, there are a few on Continentals that are a tricky to get to. I've had to weave multiple extensions with multiple swivels to be able to get so I could get a good enough grip to tighten them.
 
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