miyu1975

miyu1975

Well Known Member
I recently completed my CI and did a test flight today. Everything seemed all normal at first. As I climbed out of the pattern and into 3000 I quickly noticed engine roughness. Then looking at the engine gauges I saw number 2 cylinder CHT rising through 400 and the EGT dropping to about 1000. I quickly reduce power and headed back to the airport. Upon descending to about 2000 ft the temps came back to almost normal (although #2 egt was about 100 degrees less than the others which isn't normal). I landed pulled the cowl and visually inspected everything. Saw no visible issues so I put the cowl back on and tookoff. I stayed above the airport. And again upon climbing to 3000 ft egt dropped and cht rose... Landed again.

The only thing I did during the CI was change the intake gasket. Thinking that was a good idea for some reason. I only had 2 gaskets on me, so I changed number 2 and 4 intake gaskets. (before I ordered more gaskets someone told there is no need to proactively replace these gaskets, so I did not change 1 and 3)

My thinking is I have an intake leak most likely from the gasket. Is my thinking correct here.? Climbing in altitude is causing more air to leak and thus lean out the cylinder... ??

thanks for the help.
 
Hard to say without knowing where the mixture was. If full rich then an induction leak would lean it, and EGT would rise, not fall. Altitude would not matter, but throttle position would. Full throttle and the induction pressure is close to ambient, so little extra air is drawn in. Part throttle, induction pressure is lower, it should suck more air in thru a leak. That doesn't sound like what you described. I'd pull the plugs and look at them. Any evidence of a hot spot causing pre ignition?
 
Hard to say exactly where my throttle and mixture were and my data logs didn't download correctly. Going off of memory I believe I was about 24/2400 and I had only slightly leaned the mixture when #2 temp issue occur (so it would have been pretty rich). I did enrichen at first sign of high CHT but that didn't seem to help. I also recall what did help was pulling the throttle way back.
 
Some more VAF searches I am thinking maybe I have pre ignition issue too... Guess I will take a look at the plugs and retime my P Mags.

"Pre-ignition is the initiation of the flame front BEFORE the planned spark ignition event. It is a normal flame front, just started too soon. As opposed to detonation where EGT is little changed, pre-ignition results in rapidly falling EGTs and rapidly rising CHTs." walter Atkinson
 
Ryan, check your injectors. A little trash in one and I mean a pin head size will cause a lot of sudden roughness
Jack
 
Yep, that sounds a lot like preignition. A partially clogged injector should spike the EGT, because of a leaner mixture.
Intake leaks show up at low manifold pressure. Manifold pressure is actually a vacuum at low MP and ambient air at high MP. There's no reason for air to go through the leaky intake seals when the tubes are open to nearly ambient air pressure.

I would check and even replace the plugs in that cylinder, and borescope it.
Sometimes the ceramic insulator is cracked and it's not visible.
What type/brand plugs are you using? Apparently Champions are notorious for cracked insulators.

Can you try downloading the data again from your engine monitor?

I'm sure those with vastly more knowledge will chime in here shortly, I just want to make sure you are concerned enough to not go flying it to see if it goes away, cause if it is preignition it won't be pretty :)
 
Ignition wires?

Assuming ignition for the moment, see if you can isolate which ignition is bad, turn one off at a time and see which one is causing the problem. If you find one system bad, swap out the #2 wire on that system onto another cylinder (or system) and see if the problem travels with it.
If misfiring the egt would go up when one system went dead (misfire or short to ground of a single wire, or one system turned off) , if cross firing the spark can jump onto another lead and who knows where it goes, but it can fire the wrong cylinder at the wrong time, so don't mess around too long with your testing.
Higher altitudes will stress the system and may be why you don't see it on the ground. You can test the leads resistance and see if it meets spec in the the Pmag manual, but you can also have an insulation breakdown, and that won't show up on the ohm meter.


Tim Andres
 
Ok, I have a theory that came to me last night while looking over the troubleshooting Lycoming guide.

One topic was, "Cannot reach specified Altitude" Cause "Dirty induction Air Filter"

This got me thinking. I did clean and reoil my k&n filter. The recharge kit I bought this time came with a squirt bottle of oil, rather than the spray can I was used to. Because of this I way way over oiled the filter. After it set for a day or 2 dripping oil I wiped it clean then installed on the plane. Then a day or 2 later noticed red oil dripping from it so I removed, washed and lightly oiled again.

So my thought is that it is still over oiled and the engine cannot get the air it needs. This would explain the engine roughness while climbing. The more altitude is going to put it more and more lean. Yes number 2 cht was the highest but #3 wasn't far behind. I have the Rod Bower ram air set up. So I can easily test this theory and open the butterfly valve and fly filterless.

This would also, I believe, explain the excessively wet spark plug on #2. It's getting fuel, spark, just no air at altitude...

Any thoughts on this?
 
Last edited:
miyu1975 said:
So my thought is that it is still over oiled and the engine cannot get the air it needs.....I have the Rod Bower ram air set up. So I can easily test this theory and open the butterfly valve and fly filterless. Any thoughts on this?
Click to expand...

When running with the butterfly closed, the RB reed valves are likely to be far more restrictive than any amount of oil in the filter.

Did you inspect the plugs?
 
Intake gasket

If your new intake gasket is leaking, then your symptoms are right on. Been there done that. Pull the intake tube again and make sure the new gasket is seated correctly. An air leak at either end of the intake tube will case what you experenced.
 
Dan... I pulled the plugs too.. #2 was very wet and they were brand new to start with. I pulled #1 and #3 to compare and they looked perfectly normal.

perhaps the combination of reed valve restriction and excessive oil has caused this issue to arise.
 
Last edited:
also, I replaced the #2 gasket again, with a new one. This didn't help any. My engine is the IO 360 A1A where the intake tube go into the sump. ie..they are not connected with the rubber hose and clamps.
 
If you had pre-ignition for more than about 10 seconds, you'd probably have a hole in the piston and, the ground electrodes would probably be distressed or gone too. Worth checking the injector in the offending cylinder anyway.

As others stated, an induction air leak will show up much more at idle and part throttle, very little near WOT because there is almost no pressure differential between ambient and manifold.

You might also look the at temp probes and instrumentation since high CHTs and low EGTs don't make much sense if the engine is continuing to produce decent power and is running smoothly. If you can, swap the probes.
 
rv6ejguy said:
If you had pre-ignition for more than about 10 seconds, you'd probably have a hole in the piston and, the ground electrodes would probably be distressed or gone too. Worth checking the injector in the offending cylinder anyway.

Well I didn't see any hole in the piston, so glad there. I did remove the injector, I looked fine. I cleaned it up too.

As others stated, an induction air leak will show up much more at idle and part throttle, very little near WOT because there is almost no pressure differential between ambient and manifold.

But what would you expect, if the air filter was almost totally clogged?...runs fine on the ground. but I as climb alt the engine gets rough. Air gets thinner with altitude and if the engine is already deprieved of air on the ground it will only get worse with altitude. (am I trying to convince myself)...

You might also look the at temp probes and instrumentation since high CHTs and low EGTs don't make much sense if the engine is continuing to produce decent power and is running smoothly. If you can, swap the probes.
Click to expand...

As I climbed into 3000 ft. the engine gets rough...easy to spot and the temps then start moving. Makes me think the probes are telling the truth.
 
miyu1975 said:
Ok, I have a theory that came to me last night while looking over the troubleshooting Lycoming guide.

One topic was, "Cannot reach specified Altitude" Cause "Dirty induction Air Filter"

This got me thinking. I did clean and reoil my k&n filter. The recharge kit I bought this time came with a squirt bottle of oil, rather than the spray can I was used to. Because of this I way way over oiled the filter. After it set for a day or 2 dripping oil I wiped it clean then installed on the plane. Then a day or 2 later noticed red oil dripping from it so I removed, washed and lightly oiled again.

So my thought is that it is still over oiled and the engine cannot get the air it needs. This would explain the engine roughness while climbing. The more altitude is going to put it more and more lean. Yes number 2 cht was the highest but #3 wasn't far behind. I have the Rod Bower ram air set up. So I can easily test this theory and open the butterfly valve and fly filterless.

This would also, I believe, explain the excessively wet spark plug on #2. It's getting fuel, spark, just no air at altitude...

Any thoughts on this?
Click to expand...

But why just #2? The symptoms do not match a clogged air filter, it would affect all cylinders, I've experienced it after a wash job with a wet filter. it affects the engine totally.

Your plugs are wet, both of them. Ignition is not occurring because of a timing issue? Not likely on just one cylinder.

Perhaps a valve is not seating properly?

If the engine was ok before the CI and gasket change, something may not be right with that tube.

I'd have an experienced mechanic check it over.
 
David-aviator said:
But why just #2? The symptoms do not match a clogged air filter, it would affect all cylinders, I've experienced it after a wash job with a wet filter. it affects the engine totally.

Your plugs are wet, both of them. Ignition is not occurring because of a timing issue? Not likely on just one cylinder.
Click to expand...

No ignition, would have really low EGT and CHT though plus something like a 30% loss in power.
 
I don't want call it done without a few more flights, but I believe the issue is resolved. Before I flew yesterday I did a quick compression check on #2 and it was fine 78/80. I flew for 15 or so minutes up to 3500 with unfiltered air the whole flight. I did not experience any of the issues I had in the previous 3 flights.

Looking at the data logs for the previous flights #2 was running hottest and first to respond in temp change with increasing altitude, but #3 wasn't far behind. Not sure why #2 was first to have the temps go up like it did, perhaps it is running the leanest already.
 
miyu1975 said:
I don't want call it done without a few more flights, but I believe the issue is resolved. Before I flew yesterday I did a quick compression check on #2 and it was fine 78/80. I flew for 15 or so minutes up to 3500 with unfiltered air the whole flight. I did not experience any of the issues I had in the previous 3 flights.

Looking at the data logs for the previous flights #2 was running hottest and first to respond in temp change with increasing altitude, but #3 wasn't far behind. Not sure why #2 was first to have the temps go up like it did, perhaps it is running the leanest already.
Click to expand...

The compression check is smart, although it doesn't totally discount a valve problem.

Regarding air filter oiling...did you switch back and forth between filtered and unfiltered air at 3500 ft?

In any case, a restricted air filter doesn't make a Bendix/Precision/AFP style injection system go lean. Fuel metering is velocity based, fundamentally a differential between dynamic pressure and venturi pressure. The system moves toward rich as density is reduced by altitude or intake restriction.
 
DanH said:
The compression check is smart, although it doesn't totally discount a valve problem.

Regarding air filter oiling...did you switch back and forth between filtered and unfiltered air at 3500 ft?

I probably should have, but did not. I did not want to induce high CHTs again.

In any case, a restricted air filter doesn't make a Bendix/Precision/AFP style injection system go lean. Fuel metering is velocity based, fundamentally a differential between dynamic pressure and venturi pressure. The system moves toward rich as density is reduced by altitude or intake restriction.
Click to expand...
Good point on making it rich instead of lean at altitude with a restricted intake filter. Perhaps that would explain the fuel soaked plugs on #2?
 
You must log in or register to reply here.