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low egt reading # 4 cylinder


timj0rdan86

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good morning everyone i own a 67 mooney taking off to day from my home airport everything was a ok, on the return flight i heard a slight vibration then i look at my egt #4 reading approximately 200 lower than other cylinders cht normal. in the descent to land heard popping sound from engine and running rough 

 

no oil on the screen, all other indications normal 

 

suggestions or thoughts

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EI makes several engine monitors. Which one do you have?

The lean mag check is done in flight. You need an engine monitor that shows all four EGT temps and all four CHT temps. While in flight and leaned out for cruise flight, do a mag check. But leave it on each mag for at least 30 seconds. 1 minute is even better. Note if there is an EGT drop to zero on any one cylinder and which mag you were on when it went to zero. That will tell you which plug is not firing.

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8 hours ago, timj0rdan86 said:

good morning everyone i own a 67 mooney taking off to day from my home airport everything was a ok, on the return flight i heard a slight vibration then i look at my egt #4 reading approximately 200 lower than other cylinders cht normal. in the descent to land heard popping sound from engine and running rough 

 

no oil on the screen, all other indications normal 

 

suggestions or thoughts

One fouled plug will result in HIGHER EGT.  Your EGT should not be lower from a spark plug problem, right?  Even if both are fouled and firing intermittently, you'll still get a higher EGT (unless both are not firing the majority of the time).

The only thing that would REDUCE your EGT would be if the cylinder is intermittently not firing.  This could be an ignition problem that happens to affect both plugs, but I'd put more money on a fuel or air problem.

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7 hours ago, jaylw314 said:

One fouled plug will result in HIGHER EGT.  Your EGT should not be lower from a spark plug problem, right?  Even if both are fouled and firing intermittently, you'll still get a higher EGT (unless both are not firing the majority of the time).

The only thing that would REDUCE your EGT would be if the cylinder is intermittently not firing.  This could be an ignition problem that happens to affect both plugs, but I'd put more money on a fuel or air problem.

During a mag check, while running on a single mag, only one of the plugs in each cylinder is firing. This will normally result in an EGT rise. But if one of the plugs is fouled and not firing at all, when on that mag, the EGT will drop to basically zero. There's no fire in that cylinder. This will pinpoint the offending plug. 

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Oh now we have to say the why of pulling plugs.    You heard a "popping sound"  which would say that unburned gas was going against a hot exhaust and firing off (when was the muffler last inspected)   Pulling plugs is one thing you can do as an owner/pilot.    Pulling plugs will tell you alot about what is going on.  You could even stick a camera down there and see things.   https://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

What was DA when you landed?   Did you go full rich prior to landing?   What plugs are you running? 

Also you are pulling the plugs so you open the cowl.  Which means you can look around for lots of things that are out of order and clean things up and see things that might not be right.   You need a good flashlight and a good eye.

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i took the cowl off this morning no leaks of oil anywhere or anything abnormal visually and checked just under 6 quarts(normal) in the engine, and the temps never got hot. The DA that day was around 5k, 

it is still running rough and engine monitor still reads the same #4 bar graph was rising /egt readout  about 1000 all others Lean of Peak 1290-1350 @ 2000 rpm

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29 minutes ago, timj0rdan86 said:

i took the cowl off this morning no leaks of oil anywhere or anything abnormal visually and checked just under 6 quarts(normal) in the engine, and the temps never got hot. The DA that day was around 5k, 

it is still running rough and engine monitor still reads the same #4 bar graph was rising /egt readout  about 1000 all others Lean of Peak 1290-1350 @ 2000 rpm

 

23 minutes ago, 1964-M20E said:

Do you have an E or C model i.e injected or carburetor?   Pull the injector on #4 and clean it you might be running very lean.  Check the intake tube and intake for leaks as well.

Did you run a mixture sweep to see where #4 peaks?  That might give you an idea as to whether the #4 cylinder is lean or rich compared to the other cylinders, and that might narrow down the problem.

Also, check the #4 EGT probe.  EGT #4 peaks at the same mixture as all the others, a sensor problem is another possibility.  I found one of my EGT probes had come loose and had almost completely backed out of the exhaust downpipe once.

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As I found out 5000 DA and full rich is not the best combination and can foul the plugs.  West Texas Hot and 5000DA changed where the idle mixture was set from about 3/8 to about 1/4 of the mixture range.   If you went full rich for the pattern may have fouled the plugs.   I was taught to leave mixture to cruise setting and then shove everything forward if I needed a go around.

Did you try and burn things off?   I did 1700 RPM and cruise lean for several minutes to burn them off.   Still running crappy and found the bad plug when I pulled them.

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Is yours fuel injected?  I had the same symptom on mine a few weeks ago.  It showed up first as a vibration that got worse as I leaned the engine.  I then noticed the EGT on #4 was higher in my case and the CHT was lower than the rest.  I read about the inflight Mag check and when I took her back up, I did the mag check.  It showed an intermittent misfire on #4.  Was actually bad enough that if I didn't run full rich, the whole panel/plane would vibrate pretty badly.  Went through the normal checks with the A&P when I got back.  Checked the injector, no signs of dirt but cleaned it while we had it out.  Checked the flow flow with the adjacent cylinder and saw nothing wrong.  Checked spark plugs and found nothing wrong, but cleaned them while we had them out.  They had also just been replaced at annual a few hours before.  Bore-scoped the cylinder and found nothing wrong.  Test flew it again and everything worked fine. Better than ever actually.  Was able to get her to lean of peak for the first time ever.  Still not sure what was actually wrong, but glad it

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Tim,

You seem to have a significant problem solving effort coming...

Consider the following...

1) be clear what engine you have.... update your avatar.

2) be clear about what data you have... what engine monitor model you have.

3) Solving engine problems happens quickly around here with data...

4) If you have engine monitor data and graphs, post them...

5) take the next logical steps...

6) flying it to see what happens next isn’t the next logical step...

7) Do you know what spark plugs you have in there? How old? Can you check their resistance? Do they say champion on there?

8) Are you familiar with how to test the flow rate of your fuel injectors? Baby jar test? Cleaning using Hopp’s?

9) What density altitude were you seeing at T/O?  Did you lean the mixture to match the DA?

10) describe the run-up... If it is spark related, this should show something interesting...  if it is fuel injector related the EGT rise should show something...

These are the usual starting points discussed on MS.

Assumptions can be extra bad if the DA is high... and the engine isn’t producing power...

PP thoughts only not a CFI or mechanic...

Best regards,

-a-

 

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