So here's a weird one. EGT Anomaly

EdFred

EdFred

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What say you?

Had a cylinder running high CHTs, normal EGT's after my "top". Pulled the cylinder and send it back in to have it redone. Get cylinder back and put it on, and break it in. CHT is right in line with the other 5. But then it gets odd.

When below 1200 RPM, the EGT on said cylinder shows 700F cooler than all the other EGTs.
When between 1300 and 1500/1600 RPM said cylinder is 400F higher than all the other EGTs
When at cruise power the EGT is in line with the other five.

So, we swapped probe channels to see if it's an instrument issue. Nope, the problem just moved channels as expected.
Install new EGT probe. Same issue.
Replace spark plugs. Same issue.
Check compression and intake/exhaust for leaks. Same issue.
Pull valve cover, check tolerances. Same issue.
Inspect cylinder with camera, all is in order. Same issue.
Re-seat and seal standby vac hose that's on the intake. Same issue.
Mag check at all RPMs, normal. Same issue.

Thoughts?
 
Check again.

<check exh leak too>
 
Wrong answer. We spent 2 days on it. It was checked. Both of them.

I'm now remembering why I left here for 3 months.
 
You can leave again if you like. The numbers say change in A/F ratio.

Only other idea I have is a lifter pumping up and holding a valve open. But, the EGT numbers are backward for that event.

<edit, I meant lifter holding the valve. My bad>
 
And perhaps you can't read where I said that was checked and double checked. Did you even bother to read where I went through everything we did?
 
Too bad there really isn't a way to see what injectors are doing while it's running. Anyone ever had idle troubles cause by the distribution valve?
 
Oh, yeah, it's carb'd not injected. That was part of the discussion with the IA, "if it was injected that would be one more thing to check, but..."

Thing is, it runs smooth.
 
bnt83 said:
Too bad there really isn't a way to see what injectors are doing while it's running. Anyone ever had idle troubles cause by the distribution valve?
Click to expand...

Injectors would be a good guess! Ed Dead! Clean your injectors?

But to answer your question the "spider valve" is really not a valve at all. It simply flows fuel to each cylinder. It is certainly possible that line is restricted! Ed Dead! Blow air through the line to that cylinder and retest!

For those wondering what I am talking about, "fuel injection" is a misnomer by today's definition. Fuel is continuously flowed into each cylinder based on pressure and injector nozzle size though the "spider" valve. It never stops like today's injectors. Certainly, the new injection systems are attempting "injection" but in aviation the general term "injection" actually means "fuel flowing".

Flame away you late to the thread Monday morning QBs, but I answered it first. :lol: :mad:
 
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EdFred said:
Oh, yeah, it's carb'd not injected. That was part of the discussion with the IA, "if it was injected that would be one more thing to check, but..."

Thing is, it runs smooth.
Click to expand...

I've found loose tubes in the oil sump but I would think you could find those via vacuum leak test.

Makes sense if a hydraulic unit had excessive leakage that pumps up on higher rpm
 
I have observed this phenomenon in Ed's bird- very odd, indeed. I am stymied.
 
Say 700 RPM what do EGTs do when running on one mag at a time? Repeat at 2000 rpm.
 
I take it you have ruled out instrument error.
 
Sounds like a bad valve...3rd overhaul is the charm
 
EdFred said:
That was the first thing I checked.



Checked em both. Seated perfect. No blow by.



We did.
Click to expand...

Well, seems like the cylinder has an issue. Pull it apart again and dye pen check it for cracks, valve seats and all? Perhaps a problem in the Acme threads?:dunno:

Oh, how about a spark plug problem? Are you FI or Carb?
 
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Henning said:
Well, seems like the cylinder has an issue. Pull it apart again and dye pen check it for cracks, valve seats and all? Perhaps a problem in the Acme threads?:dunno:

Oh, how about a spark plug problem? Are you FI or Carb?
Click to expand...

mag timing....seriously I'm guessing but it's the one thing I haven't seen.
 
One thing that pops up on occasion is weak valve springs, but IDK if they could cause these symptoms.
 
So, how do you get 700 degree swings in EGT with no change in CHT for that cylinder if the problem is vacuum leaks, valves, etc?
 
Dry tappet clearance checked?
 
EdFred said:
What say you?

Had a cylinder running high CHTs, normal EGT's after my "top". Pulled the cylinder and send it back in to have it redone. Get cylinder back and put it on, and break it in. CHT is right in line with the other 5. But then it gets odd.

When below 1200 RPM, the EGT on said cylinder shows 700F cooler than all the other EGTs.
When between 1300 and 1500/1600 RPM said cylinder is 400F higher than all the other EGTs
When at cruise power the EGT is in line with the other five.

So, we swapped probe channels to see if it's an instrument issue. Nope, the problem just moved channels as expected.
Install new EGT probe. Same issue.
Replace spark plugs. Same issue.
Check compression and intake/exhaust for leaks. Same issue.
Pull valve cover, check tolerances. Same issue.
Inspect cylinder with camera, all is in order. Same issue.
Re-seat and seal standby vac hose that's on the intake. Same issue.
Mag check at all RPMs, normal. Same issue.

Thoughts?
Click to expand...

So, you swapped the channels at the back of the analyzer to rule out a problem in the analyzer. You replace the actual probe to rule that out. What about the wiring between the probe and the display? I assume that hasn't been changed. Can you swap the wires from one EGT probe to another and see if it follows the wires or sticks with the cylinder?

I would think that if it was a combustion issue you would see changes in the CHT that either matched or were opposite to the changes in EGT.
 
Yes, we swapped the wires as well. We are stumped.

It's an O-540, and we checked the clearances twice. Doubt it's a cam issue, as it isn't making metal and when we had the cylinders off everything looked outstanding wear-wise.
 
EdFred said:
Yes, we swapped the wires as well. We are stumped.

It's an O-540, and we checked the clearances twice. Doubt it's a cam issue, as it isn't making metal and when we had the cylinders off everything looked outstanding wear-wise.
Click to expand...

Did you check the metal intake pipe on the cylinder? :dunno:
 
EdFred said:
Yeah, that's where the standby vac line is. And that line looks good, and my vac system is running normally as well.
Click to expand...

If it was me, I would remove the line and pressure check it for leaks. Also the shuttle valve on the standby vac.

Also check where the line is connected to the steel pipe for leaks.

I'm willing to bet your problem is coming from the standby vac line.

Another check is to remove the standby vac line, seal off the hole and run it, check readings.
 
Wasn't there an AD on precise flite standby vacuum valves a while ago?
 
Ed,

Are any of the wires for the engine analyzer running close and parallel to the ignition leads or alternator A+? They can induce a current in the analyzer wiring.
 
Norman said:
Ed,

Are any of the wires for the engine analyzer running close and parallel to the ignition leads or alternator A+? They can induce a current in the analyzer wiring.
Click to expand...

This is a fine suggestion and one that may have been overlooked. A little aluminum foil band aid to verify would be simple if it was the issue.
 
TEFLONSEAN said:
This is a fine suggestion and one that may have been overlooked. A little aluminum foil band aid to verify would be simple if it was the issue.
Click to expand...
'cepen he swapped the wires between cylinders - if this were the case, it would follow the wires, not the cylinder. :dunno:
 
Was going to get out to the airport Saturday, but couldn't pass up year end deal of 18 holes and a cart for $10. Yesterday was yard work around the house.
 
Capt. Geoffrey Thorpe said:
'cepen he swapped the wires between cylinders - if this were the case, it would follow the wires, not the cylinder. :dunno:
Click to expand...

If the swapped wires happened to get routed in the same problematic way then it would follow the cylinder. But that's not necessarily likely.
 
My #5 was overhauled at only 200 hours SMOH due to a bad oil scraper ring...it was bad from day one...likely broken during reassembly.

Ever since (almost 1000 hours) #5 has run at a much lower EGT than the others on take-off and climb. Many times 300 to 400 degrees lower.

Then, once I get to cruise altitude, trim, and do engine management, it falls right into line with the rest. On many days I'll see EGT spreads of 20dF or less.

I spent a fair amount of money chasing the issue initially, to no avail. This included swapping probes, new probes, OH'ing the intake system including all new gaskets and flexible connectors, new exhaust gaskets, etc., etc.

All to no avail.

I finally just learned to live with it and it's run over 1000 hours trouble free so I just chalk it up to "it is what it is".
 
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