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#4 EGT higher than the others in idle

RV74ME

Well Known Member
Today while practicing simulated engine out glide to the airport, I noticed my #4 EGT was quite a bit higher than the other 3. In idle, 1-3 were all pretty even, somewhere around 700-800. #4 was more like 1100-1200.

When I push the throttle above idle, they all pretty much even out. No other abnormal indications. CHTs were all pretty even. And it’s a Lycoming IO-360M1B.

Any ideas?
 
Induction leak.

You’re suggesting that the engine is running 400* rich of peAk At idle? Most engines are set to around 50 ROP at idle. How does a lean condition raise EGT 400* at idle?

To the OP, i would be looking for a bad or fouled plug on that cylinder. Reduced timing raises egt. Though I wouldn’t expext that high of an egt delta. Could also be an issue with the probe.
 
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Has to be one of the following.
Bad EGT probe
Poor electrical connection/ground
induction leak
timing issue
small piece of trash??? stopping the exhaust valve from completely closing.

Your symptoms seem to me to indicate one of the first two
 
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Has to be one of the following.
Bad EGT probe
Poor electrical connection/ground
induction leak
timing issue
small piece of trash??? stopping the exhaust valve from completely closing.

Your symptoms seem to me to indicate one of the first two

Ok, I will check the plugs and maybe try another probe
 
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I had the same issue on a IO540. What was the temperature and DA at your airport? Turned out I was running very rich with a 4000 foot DA on downwind with very high temps. Plugs unable to Fully fire the charge and fuel burning in the exhaust. Leaning slightly solved the issue. Replacing my top auto plugs that were slightly worn seems to have cured it completely but have not been able to flight test in those temps again. If it happens again lean a bit and see if that solves it in the pattern.
G
 
I had the same issue on a IO540. What was the temperature and DA at your airport? Turned out I was running very rich with a 4000 foot DA on downwind with very high temps. Plugs unable to Fully fire the charge and fuel burning in the exhaust. Leaning slightly solved the issue. Replacing my top auto plugs that were slightly worn seems to have cured it completely but have not been able to flight test in those temps again. If it happens again lean a bit and see if that solves it in the pattern.
G

Good advice, I will try that. But not sure that was my problem, as I went to idle from 5000’ (where it was a little cooler than the 90 deg surface temp) and still got the indication.
 
One other thing I forgot to add to the list is one of your spark plugs not firing which causes the exhaust gases to burn slower as they exit down into the exhaust thus increasing the EGT. A bad or fouled plug or plug wire. Just another thought. (I'm still betting on one of the first two above).
 
Good advice, I will try that. But not sure that was my problem, as I went to idle from 5000’ (where it was a little cooler than the 90 deg surface temp) and still got the indication.

If you were full rich at 5000 it would cause the problem. If you were leaned than I would chase the induction leak.
 
Checked for induction leak...no blue fuel stains anywhere I can see.
Tried new egt probe and test flew. Indications all the same. Went to idle and watched all egts come down together, then #4 rose above the other 3. Did inflight mag check (in idle). All appeared normal, so spark plugs are ok.

Gonna keep monitoring, but maybe I’m trying to see a problem that doesn’t really exist.🤷🏼*♂️
 
Checked for induction leak...no blue fuel stains anywhere I can see.
Tried new egt probe and test flew. Indications all the same. Went to idle and watched all egts come down together, then #4 rose above the other 3. Did inflight mag check (in idle). All appeared normal, so spark plugs are ok.

Gonna keep monitoring, but maybe I’m trying to see a problem that doesn’t really exist.🤷🏼*♂️

Search "EGT" in this doc. Suspect you have an injector acting up.

https://www.lycoming.com/sites/default/files/SSP-475.pdf
 
Checked for induction leak...no blue fuel stains anywhere I can see.
Tried new egt probe and test flew. Indications all the same. Went to idle and watched all egts come down together, then #4 rose above the other 3. Did inflight mag check (in idle). All appeared normal, so spark plugs are ok.

Gonna keep monitoring, but maybe I’m trying to see a problem that doesn’t really exist.🤷🏼*♂️

Any updates? Curious if you found the problem (or non-problem).
 
Do you have an EFIS and a Savvy Pro Account?

If so they offer an “Induction Leak Test”.

This test is interesting because it is so easy. You climb up to and level off at 5,000 MSL and if you have a constant speed propeller set the RPM to 5,000 RPM.

For normally aspirated engines you run the throttle at WOT and for turbocharged engines you set the MAP at 24.8 IN HG and wait for everything to stabilize and let the EFIS system capture the EGT data and RPM. All you have to do is record the time and enjoy the scenery.

Then the next step is to adjust the MAP to 14.8 IN HG (doesn’t matter if the engine is turbocharged or not) and remain level at 5,000 MSL and wait for everything to stabilize and record the time again.

Constant speed propellers will keep the RPM stable at 5,000 RPM and a consistent RPM is ideal. Fixed pitch propeller engines just level at 5,000 feet MSL and do WOT for the first step and then for the second step just reduce the throttle to about 80 percent of the max lever travel…in other words full up for the first step and slightly back for the second step because you most likely do not have a MAP indicator and you can’t control RPM so you get what you got.

When you get back down on the ground upload the engine data to SAVVY and set up a support ticket and notate the two times on the ticket and that you performed the Induction Leak Test and they will tell you if your intake manifold system is leaking or not.

How do they do that? At 5000 feet MSL the ambient air pressure is 24.8 IN HG and that is what you will see on the MAP indicator of a normally aspirated engine. OK there might be a slight difference because the throttle valve and the air filter might create a 1 inch drop but if you have a scoop for the intake air it might recover some of that drop. The turbocharged engine operator was asked to set 24.8 IN HG for their MAP so same-o…same-o. At this MAP there is almost no appreciable difference in air pressure from what is outside the intake manifold to what is inside the intake manifold. The SAVVY technician will look at the stabilized EGT for each cylinder at the time you recorded.

Then they will look at the EGT values for the 14.8 IN HG MAP at the time you recorded and compare the difference between the high pressure EGTs verses the low pressure EGTs. Cylinders that have a leak in their induction system will be identified as running leaner at 14.8 MAP than the cylinders with no induction leak.

Why? Because the high power MAP throttle setting had almost no difference in air pressure from outside of the intake manifold system to the inside of the intake manifold so there is effectively no leak being observed whereas the 14.8 IN HG MAP throttle setting will have a 10.0 IN HG air pressure difference and with the more restricted throttle valve the engine will be trying to suck air from anywhere it can and it will get its air from the leaking intake pipe and this will result in a much leaner mixture and the leaner mixture will produce warmer EGTs for the affected cylinders.
 
5,000 RPM?

...
This test is interesting because it is so easy. You climb up to and level off at 5,000 MSL and if you have a constant speed propeller set the RPM to 5,000 RPM.

...

Constant speed propellers will keep the RPM stable at 5,000 RPM and a consistent RPM is ideal. Fixed pitch propeller engines just level at 5,000 feet MSL and do WOT for the first step and then for the second step just reduce the throttle to about 80 percent of the max lever travel…in other words full up for the first step and slightly back for the second step because you most likely do not have a MAP indicator and you can’t control RPM so you get what you got.
...
Very cool tip - didn't know this! Do you have a typo in the above - perhaps you meant to write 2500 RPM?
 
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