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Low EGT at Low Power

Jeff Vaughan

Jeff Vaughan

Well Known Member
I sure could use some help trying to figure out my engine issue.

I have installed on my TMX-0360 a LSE Plasma II+ on
my right and a mag on the left.

I currently have 211 hours with this set up. Note all four cylinders were replaced 93 hours ago. ECI recall) Recently at mag check I noticed a drop of 60 rpm when it has only dropped 20 RPM every time prior. The engine seemed to be smooth during this run up. As I taxied to take off I noticed that the egt temp on my # 3 cylinder was much lower than the other three cylinders 1,2,4 were 950 #3 550. When I applied power to check the mags again all EGT temps were about the same.

I checked the compression and it is fine.

I changed the plug, no difference. Put a new plug in and no difference.

Made sure wires are all snugged

I then restarted did the mag check with same non normal results. I did circle around the airport at 60%. CHTs were normal and EGTs were normal. Came in and landed and I noticed on roll out with throttle pulled all the way back the #3 EGT had fallen much lower in reference to the others. The engine was running rough as I taxied back on low power.

Got any ideas?

PROBLEM SOLVED SEE POST #15
 
Last edited:
Some ideas to check, in no particular order

Timing
Spark plug lead
Valve lifter (dry tappet clearance)
 
I will swap the leads and see what I get.

Timing - would I not have issues on other cylinders as well if it were not correct ?

Thanks
 
Sensor swapped - no change

Klaus at Lightspeed has suggested swaping the 3 and 4 plug wire as they get their spark from the same coil. If the problem moves to cylinder #4 I need to replace the coil.
 
That sort of makes sense to me...but what exactly is giving the cooler cylinder ANY heat if the coil is bad?
 
No Joy

Changed wires at coil - no change
Swapped out plug wires - no change

Believe Lightspeed is fine- it must have a bigger noticable change in RPM drop than the mag so now I suspect some thing wrong at the cylinder.

Rought idle low RPM does not smooth out over time. Lagging EGT and CHT at start up and low RPM
 
Just a horrid thought :eek:

Low EGT without say a really high CHT which would indicate preignition, and that would be bad.

But given you have a normal CHT, or seems normal, it is entirely possible there is a lack of fuel and air getting to that cylinder, just like running an injected engine lean of peak and the injector clogs a bit, you et a further drop in EGT and a slight drop in CHT also (but may not notice).

You also get some rough running at low power.....like a cylinder not firing properly.

Now, just food for thought when you run out of things to look at. Cylinder head inspection for broken valve springs? Check the lift you are getting? Failed lifter or cam lobe perhaps?

I hope it is just a dodgy plug, but you could do well with thinking of whats next in the "look see" department.
 
EGT

Just another guess. Make sure your intake gasket is seated on the head @ #3 so you are not sucking in outside air.
 
Jeff
When I first ran my IO360-A1B6 I had a pmag problem that turned out to be the coil. since you swapped out the 3-4 wires and it didn't follow the wire, then it is likely not the ignition.

Maybe I missed it, but when you are getting the 60 rpm drop, you are running on the mag or does it have the 60rpm drop on both?

On my set up the mag plugs are on the bottom. they are more prone to fouling. with ignition problems to start and then high oil temps after first flight, I didn't get a good ring seating and had high oil consumption which has settled out after 75hrs but short story is the bottom plugs get most of the fouling. It can be firing, but weakly or intermittently. You can be get a situation where it is not firing consistently reducing the egt. with both mags running it runs fine with normal egt.

Clean / change the mag plug and then try your run up at around 1800 rpm.
 
Problem Solved

After rechecking the compression and both ignition systems plugs wires etc
I deceided to talk to our local A & P regarding checking the lifters. He asked me to check with Mattituck to see what dimension the exhaust valve guide should be reamed to if we find a hung exhaust valve and to get another opinion. I left a message on Mahlons voice mail and I received a call back in less than 5 minutes. He told me the symptoms were "classic intake leak"
Low EGT , CHT on low power Rough running
OK EGT, CHT on cruise power Smooth running

I had taken off the intake tube to look for cracks or messed up gasket. Nothing found. Put it all back together and took one last look at any possible places where a leak could happen. I inspected the Manifold pressure line FWF. Everything fine. Now behind the firewall I found my tygone tube had come loose and was disconnected from the T where the line split to the pressure sender and the LSE box.

Very simple fix. Mahlon Rocks !!!

Thanks to all that offered suggestions.
 
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