What happened to my cylinder on start?

[Nikhiln25]

Today I had a very interesting anomaly on start. After 4 hours of running the pre heater, I started the engine with 3 shots of primer as I normally do. I'm getting the plane configured and I start hearing a very faint Pop pop pop..one of the cylinders were misfiring. I noticed it immediately on the JPI that on cylinder was extremely low EGT.

I also started to smell some burning. For whatever reason I figured im not giving it enough fuel so I put in some mixture and raised RPM. I immediately noticed EGT it coming back.

However, if I would lower RPM I would notice that one EGT once again fall (you can see ti on the chart dip a couple of times and the DIF increasing everytime I lowered RPM. I initially had the plane around 1000 RPM when I noticed the misfiring...then I raised it to about 1300. THat's when EGT started coming back. I then lowered to 1000 and noticed it coming back.

I did a couple of idle checks to see if the engine would quit...it stayed alive. I then figured to see if I could clean the spark plugs and if that would solve it. I ran the engine at run up RPM for a few seconds at a lean mixture and I did not having this problem again.

I'm not sure if I actually had a spark plug issue or a exhaust valve being stuck issue? Any perspective? I don't think a spark plug would result in such low EGT's. But then just running the engine at higher power cleaned it and it didn't happen again.

Greatly appreciate any perspective on this. I've emailed Savvy and my A&P but figuring im not hearing for a few days.

I've attached 3 pics - one showing the whole flight ( which I kept in pattern), one showing the zoom in on start and one showing the zoom with the RPM as well

 

[Checkout_my_Six]

probably a stuck exhaust valve.....or commonly referred to as morning sickness.

 

[455 Bravo Uniform]

Because you have 2 mag and 2 plugs per cylinder, one fouled or bad plug or bad mag would result in high EGT, not low. At least that’s how EG temps behave on mag checks at 1700 rpm.

 

[Nikhiln25]

Th

probably a stuck exhaust valve.....or commonly referred to as morning sickness.

Thanks! What’s usually the fix for this? Should be something my A&P be able to fix quickly? First time experiencing this

 

[Checkout_my_Six]

Th

Thanks! What’s usually the fix for this? Should be something my A&P be able to fix quickly? First time experiencing this

There is a fixture to check the valve stem play....this engine is known for accumulating carbon on the exhaust valve guide and eventually sticks. The fix is to ream/clean out the valve guide. Your A&P should be able to do this.

 

[Nikhiln25]

Savvy seems to think an induction leak is more likely than sticky valve, but advised to check both. Though if it was an induction leak, the issue should be present each time at a lower power setting? It shouldn’t only occur at start up? The other times I have the engine at idle/low power, the egts were in a fairly normal range

 

[Checkout_my_Six]

That's an easier fix.....

 

[Nikhiln25]

Wouldn't an induction leak result in low MP? My MP at idle is around 16-17, whch Savvy says is very high, and partly how they are guessing induction leak is a reason

 

[Checkout_my_Six]

Wouldn't an induction leak result in low MP? My MP at idle is around 16-17, whch Savvy says is very high, and partly how they are guessing induction leak is a reason

No....recall that the ambient atmospheric pressure is around 29.....so an induction leak will cause the MP to rise.

 

[Nikhiln25]

After a few weeks attacking this problem, I’m no closer to a solution.

First I had my A&P borescope cylinder and based on what he saw he does not believe valve is stuck. He did not (I’m not even sure if you can) see the condition of the guide - he looked at the seat and based on that he said it wasn’t.

He also turned the prop 6 times and it cleared each time (on a cold engine). He also had done a compression test and that was fine too.

he thinks it’s likely just due to the poor distribution system of the 0-470 And that when cold the fuel isn’t atomized and distributed in the best manner. He does not think there is an acute problem with the cylinder, yet the condition persist.

Couple of data points corroborate his thinking. First, on a recent start both the 5 & 6 engine were very low in start. 6 is normal on most days but on this flight it definitely took its time coming alive (see pic attached). Probability of two cylinders experiencing stuck valves at the same time seems very low.

Second I went back to my engine monitor data as far back as I could and this condition has been periodically happening for the last 2 years. I’ve noticed it in flight as far back is summer of 2023 (engine was installed in summer 2022). And it happened way more in winter than summer.

So now I’m wondering if this makes sense to anyone here? That because of the poor distribution of this engine this is what is causing this on a cold start. Also wondering if I should seek out a second opinion from another A&P

 

[Magman]

Running an O-470 with the cowl off on a cold day results in some strange

things all related to fuel distribution. I haven’t seen it on a cowled engine

though.

 

[mondtster]

Running an O-470 with the cowl off on a cold day results in some strange

things all related to fuel distribution. I haven’t seen it on a cowled engine

though.

I’ve seen the same thing. It took a while for me to figure out the connection (no cowl = bad run when cold) but after the connection is made it is predictable.

 

[Dan Thomas]

Running an O-470 with the cowl off on a cold day results in some strange

things all related to fuel distribution. I haven’t seen it on a cowled engine

though.

Yup. It's the pulsating propeller blast against the airbox that does it. It sets up a back-and-forth flow of air through the carb and causes pulsations in the induction system.

These were nor designed as ram-air systems. If you look at the cowl and how the air inlet is sloped to match the cowl's curve, you understand that the prop blast is deflected down across that air inlet so that the flow is not hammering at the inlet. The engine is free to draw in whatever it needs without being forced to swallow pulsating flow.

Some homebuilders learned this long ago. They wanted to take advantage of ram air for more performance, but their engines did not run well. Changing those inlets to face another direction often fixed it.

Ram air is way overrated. At 100 MPH it is about 0.176 psi. That would be a bit more than 0.3 inches of mercury.

 

[Gary Ward]

Yup. It's the pulsating propeller blast against the airbox that does it. It sets up a back-and-forth flow of air through the carb and causes pulsations in the induction system.

These were nor designed as ram-air systems. If you look at the cowl and how the air inlet is sloped to match the cowl's curve, you understand that the prop blast is deflected down across that air inlet so that the flow is not hammering at the inlet. The engine is free to draw in whatever it needs without being forced to swallow pulsating flow.

Some homebuilders learned this long ago. They wanted to take advantage of ram air for more performance, but their engines did not run well. Changing those inlets to face another direction often fixed it.

Ram air is way overrated. At 100 MPH it is about 0.176 psi. That would be a bit more than 0.3 inches of mercury.

I experienced this drag racing.

 

[FORANE]

Ram air is way overrated.

Dan, I respectfully disagree. The new plane I have has ram air. When it is opened while airborne on climbout there is an increase in thrust significant enough to obviously push you back in your seat.

 

[Skymac]

I had this happen on a Lycoming 580 about 2 years ago. Related to the 50hr service bulletin on intake tubes.

The flange on the intake tube was cracked and anything below about 950-1000rpm, the cylinder would pull too much vacuum / air and the cylinder would quit firing, above 1000 the air/fuel ratio would reignite and the engine ran perfectly with good egt spread, etc. Replaced the intake tube, and problem solved.

 

[Nikhiln25]

I had this happen on a Lycoming 580 about 2 years ago. Related to the 50hr service bulletin on intake tubes.

The flange on the intake tube was cracked and anything below about 950-1000rpm, the cylinder would pull too much vacuum / air and the cylinder would quit firing, above 1000 the air/fuel ratio would reignite and the engine ran perfectly with good egt spread, etc. Replaced the intake tube, and problem solved.

Thanks for sharing this. An intake issue like this will always show up right? It shouldn’t just be a start issue ?

 

[MooneyDriver78]

Dan, I respectfully disagree. The new plane I have has ram air. When it is opened while airborne on climbout there is an increase in thrust significant enough to obviously push you back in your seat.

On older Mooneys it really helps, but they redesigned the air induction system starting with the J, resulting in ram air being superfluous as it only increased the MP by small fraction, the increased drag from having a hole in the cowl negated any small horsepower improvement. They eventually dropped it, and put out a service bulletin to allow early J models to remove it.

Any modern engine system shouldn’t need it.

 

[Dan Thomas]

Dan, I respectfully disagree. The new plane I have has ram air. When it is opened while airborne on climbout there is an increase in thrust significant enough to obviously push you back in your seat.

The system has to be designed so that prop blast pulsation doesn't affect the MP. On the ground, cowl off, the pulsation is serious. In flight, cowl on, it's nothing. Your system likely has some other features to enable pressure recovery, which usually involves a divergent duct of some sort to slow the air, thereby increasing its pressure. Cessnas and other spam cans are far too crude to have anything like that.