What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

#4 EGT Anomaly

Jim P

Well Known Member
Need some hive-mind input on a #4 EGT problem.

Just completed condition inspection and was doing leak check/mag check. During annual, mags timed out right on the money, no need to adjust. Prior to CI, everything appeared normal. Plugs and injectors cleaned.

1) #4 compression 77-78/80
2) Running Tempest fine-wire plugs/ Slick mags (both overhauled at 500 hrs).
3) Idle run, all EGTs are about even, as are CHTs.
4) Doing run up, #4 EGT rises fast, ends up a good 200 degs above the other three which are about even. I can tell there's some roughness as throttle advances.
5) On mag check, seeing normal rise in EGT for both mags across all cylinders.
6) #4 lower fouls easily, and is rougher on mag check, but EGT does not fall off (at least getting partial firing) during mag check. CHT not falling off either.
7) Checked fuel flow with boost pump - #4 seems to align with others in fuel volume for given time.
8) Swapped both top and bottom plugs with #2 cylinder, one at a time, no change, so I rule out a bad plug.
9) All EGTs seem normal at idle, doesn't appear to be induction leak.

With #4 lower plug fouling somewhat, I suspect a possible issue with harness wire. What else am I missing?

Jim
 
High EGT rise can be a lot of things.
1. glowing carbon in cylinder or plug
2. running on only 1 plug per cylinder
3. leaking, sticking or bent exhaust valve.

So, lets start with wringing out Mag, lead, plug, and cylinder. Take a compression test, listen to the exhaust pipe for hissing. If the valve is sticking, try a gentle "stake" of the valve, if the leak stops, I would investigate carbon in the guide (might need a ream), broken spring, bent valve, or foreign matter on the seat.
Test the resistance of the plug wire, replace if out of tolerance.
test the plug, should be under 5000 ohms resistance. Check the plug for cracks in the porcelain, both in the barrel and above the electrode. If cracks are noted, toss it!
Check the Mags for proper internal timing (e-gap) and on aircraft timing.
Run the engine on the Mag that is rough. Note if one cylinder is cooler or hotter than the rest. Switch Mags, again, note the response. If the symptoms are the same regardless which mag is firing, then I would want to take a good look at the valves and guides. Frustrating, but can be systematically trouble shot.

DAR Gary
 
Injected?

From your mention of testing fuel flow on #4, I'm assuming this is an injected engine? So... describe more your flow test. Mixture full rich? Throttle set where during the flow test?
 
From your mention of testing fuel flow on #4, I'm assuming this is an injected engine? So... describe more your flow test. Mixture full rich? Throttle set where during the flow test?

YEs, injected, throttle full, mixture full rich.
 
Assuming you did the shot glass test on the fuel lines from the spider and it came out ok, then check for an air leak.

Run the engine at ~1500 RPM, full rich. Lean and watch EGTs. Does #4 peak before the rest (or does not peak at all). If so my guess is you have an air leak on #4.

Carl
 
Continuing this one, did a Ohm check on both sides today, and #4 was all over the place as the cable was moved, from 35 - 140 Ohms, as was #1 lower to a lesser degree. All other seemed stable when cables were moved a bit, with resistance from 37 up to 52 Ohms, but stable. Cables are circa 2006, so probably time.
 
Back
Top