Rough Running

KatanaPilot · #1 12-08-2018, 07:44 AM

I had an unusual experience on a flight back home earlier this week. Had four legs that day without issue.

Titan IO-360, Hartzell constant speed, dual Pmags, about 85 hours on the engine. It has been flawless until now. 6500 feet, about 50 degrees LOP, MP 23.6, 2400 RPM.

Started seeing erratic RPM indications, dropping as much as 150 RPM and you could feel the surging. I enrichened the mixture, brought RPMs up to 2500, still surging. Turned off one ignition - engine smooth as glass, EGT increased as expected. Assumed I had isolated a bad ignition system. Just to confirm, I turned that ignition back on, problem returned, also as expected. Turned off other ignition - expected really rough running, but engine ran smooth as glass.

Ignition systems have their own dedicated CB and lever lock switch - so it's not a keyswitch issue.

Wasn't far from home and there were no other suitable airports any closer, so continued home. Turned other ignition back on once overhead airport, engine ran fine, but power was pulled back for descent and landing.

Talked with Brad at Emag and he doesn't think it's an ignition issue.

Haven't had time to look for induction leaks, etc. but figured I'd reach out to the brain trust to see if anyone has had anything similar.

mahlon_r · #2 12-08-2018, 08:05 AM

RPM should not surge , if equipped with a cs prop. No matter how choppy the engine runs the rpm should hold steady not surge 150 rpm.
Good Luck,
Mahlon

rv6ejguy · #3 12-08-2018, 08:14 AM

The fact that you cycled the ignitions and it went away immediately likely shows it was ignition related however odd the symptoms were.

Did it continue to run smooth on both after cycling or was that something you didn't try?

scard · #4 12-08-2018, 08:29 AM

I can attest to an intermittent pmag failure causing a CS prop "surge" momentarily as it catches back up. The more intermittent it is, the more potential prop (and RPM) surge you may feel. From my direct experience. Unfortunately, the ignition failure isn't always a hard and solid failure.

Carl Froehlich · #5 12-08-2018, 09:02 AM

As you demonstrated both ignitions work if run separately, perhaps looking at common ignition issues when both are running would make a good first step. For example:
- Did you bundle any ignition wires together - if so look for cross talk.
- Did a manifold sensor line fall off (so one ignition is firing at a different timing)?
- When running one ignition effective engine timing is retarded. As the engine was smooth when on one ignition perhaps timing is too advanced. Try running with the jumper in, but first check timing (TDC for parallel valve engine or 5 degrees ATDC angle head engine).

Some other checks:
- Run up ignition check drop? Do all EGTs go up when turning off one ignition and about the same rise for each igntion?
- Ignition wire resistance checks.
- Pull the plugs and look for fouling.

Let us know what you find,
Carl

KatanaPilot · #6 12-08-2018, 11:03 AM

Thanks for the suggestions. Obviously some troubleshooting to do. Worst case is I find nothing.

I think we did a good job on the install and were careful to keep wires separated and protected.

I?ll advise as to the findings.

DakotaHawk · #7 12-08-2018, 01:28 PM

It might be a long shot, but how is your oil level? At high RPM and low oil levels, you may just be getting a surge due to varying oil pressure.

F1R · #8 12-09-2018, 09:23 AM

Quote:

Originally Posted by KatanaPilot

I had an unusual experience on a flight back home earlier this week. Had four legs that day without issue.

Titan IO-360, Hartzell constant speed, dual Pmags, about 85 hours on the engine. It has been flawless until now. 6500 feet, about 50 degrees LOP, MP 23.6, 2400 RPM.

Started seeing erratic RPM indications, dropping as much as 150 RPM and you could feel the surging. I enrichened the mixture, brought RPMs up to 2500, still surging. Turned off one ignition - engine smooth as glass, EGT increased as expected. Assumed I had isolated a bad ignition system. Just to confirm, I turned that ignition back on, problem returned, also as expected. Turned off other ignition - expected really rough running, but engine ran smooth as glass.

Ignition systems have their own dedicated CB and lever lock switch - so it's not a keyswitch issue.

Wasn't far from home and there were no other suitable airports any closer, so continued home. Turned other ignition back on once overhead airport, engine ran fine, but power was pulled back for descent and landing.

Talked with Brad at Emag and he doesn't think it's an ignition issue.

Haven't had time to look for induction leaks, etc. but figured I'd reach out to the brain trust to see if anyone has had anything similar.

IIRC this symptom was very similar about 1/2 a year or more ago. It would run fine on either ignition, but not both. The thread decayed into some guy getting flamed(somebody suggested there was excessive advance ) and I don't recall if OP ever posted the actual cause or remedy.

What version software are the Pmags? or What is the date of manufacture of your pmags?

tim2542 · #9 12-09-2018, 09:47 AM

Pull the Pmags and do the check described in the manual, that is to check the bearings for play and they turn smoothly. I?d suggest you do it when they are hot.
Tim Andres

KatanaPilot · #10 12-09-2018, 11:05 AM

The Pmags (114) were several years old, but had only test stand hours and then were sent back for inspection and upgrade to the latest firmware before being reinstalled on the engine.

The jumper is installed and I limited the maximum advance via EICAD to 30 degrees.

I'm going to go through the timing procedure again to ensure that the timing hasn't drifted and that all settings are where I want them to be.

Thanks for the advice.