Hi all-
I'm 20 hours into my Phase I and have been troubleshooting a mag-drop/rpm-drop issue for the last 8 hours. Here's my set-up:
(I)O320 with Airflow Performance FM-150
10:1 pistons
Right mag replaced with LSE Plasma III, crank angle sensor (top plugs)
Left mag Slick 4373 with massive plugs (I realize I should probably have a 4371 with 20 degrees lag, but for now I'd like to leave it as is)
Catto 3-blade
When I first ran up the engine shortly before my FAA inspection, the RPM drop with Plasma OFF was 150, and with mag OFF was almost nil (I wrote down 10 RPM on my test sheet).
RPM drops became progressively worse over the first 12 hours, and the morning I taxied out and saw a 200RPM drop on both Plasma and mag I taxied back to the hangar and grounded the aircraft until I could figure out what was going on.
My first action was to adjust the idle cutoff and idle mixture, as the engine had been idling too high. This, along with a) aggressive leaning during taxi, and b) leaning before mag/Plasma check brought the RPM drop to 150 (Plasma OFF) and 120 (mag OFF). I don't understand why adjusting idle mixture would affect mixture at 1800RPM, but it seemed to help.
I then went through the troubleshooting flowchart in the Plasma manual, as 120 is still too high a drop for Plasma. All connections, wires etc tested fine but the timing, as checked with a strobe light, was retarded 5 degrees: given a high compression engine at 8000' density altitude, idle timing (MAP disconnected) should be 16 degrees plus 1 degree per thousand feet density altitude, ie 24 degrees. MAP connected is 35 degrees degrees (density altitude apparently irrelevant in this case since max advance for engines timed for 20 degrees BTDC is limited to 35 degrees). So in short, the timing should nominally have been 24 and 35 degrees but was measured at 18 and 30.
We then rotated the crank sensor as far as the slots allowed, and this brought the firing up to spec (23/35). RPM drop is now 150 (Plasma OFF) and 50 (mag OFF). Nevertheless, the engine just doesn't feel as smooth as I believe it was during the first few hours, and I know from combing the archives here researching this problem that many with LSE Plasmas see no or negligible RPM drop mag OFF (although as noted above, I have a three-blade Catto, so less rotational mass compared to a metal prop).
I spoke with Klaus and he said to check fuel flow at idle, MAP at idle, and mag timing; if those were OK then the only thing left was to send the unit in, although he said CDI degradation drifts to advanced, not retarded, timing. I have done the first two and they seem normal (2-2.5 gph, 10.5-11.5 inHg). I have not checked mag timing since I need to give my helper a respite from my daily requests for assistance, and I wonder if there aren't other things I've overlooked that I could address first.
As a final note, the plugs all look relatively clean though a bit oily (engine seems to still be breaking in), the MAP lines and induction tubes have been thoroughly checked for leaks, and all wiring and connectors for the system have been inspected and appear fine.
So, I'm stumped. Any ideas?
Thanks,
Eric
I'm 20 hours into my Phase I and have been troubleshooting a mag-drop/rpm-drop issue for the last 8 hours. Here's my set-up:
(I)O320 with Airflow Performance FM-150
10:1 pistons
Right mag replaced with LSE Plasma III, crank angle sensor (top plugs)
Left mag Slick 4373 with massive plugs (I realize I should probably have a 4371 with 20 degrees lag, but for now I'd like to leave it as is)
Catto 3-blade
When I first ran up the engine shortly before my FAA inspection, the RPM drop with Plasma OFF was 150, and with mag OFF was almost nil (I wrote down 10 RPM on my test sheet).
RPM drops became progressively worse over the first 12 hours, and the morning I taxied out and saw a 200RPM drop on both Plasma and mag I taxied back to the hangar and grounded the aircraft until I could figure out what was going on.
My first action was to adjust the idle cutoff and idle mixture, as the engine had been idling too high. This, along with a) aggressive leaning during taxi, and b) leaning before mag/Plasma check brought the RPM drop to 150 (Plasma OFF) and 120 (mag OFF). I don't understand why adjusting idle mixture would affect mixture at 1800RPM, but it seemed to help.
I then went through the troubleshooting flowchart in the Plasma manual, as 120 is still too high a drop for Plasma. All connections, wires etc tested fine but the timing, as checked with a strobe light, was retarded 5 degrees: given a high compression engine at 8000' density altitude, idle timing (MAP disconnected) should be 16 degrees plus 1 degree per thousand feet density altitude, ie 24 degrees. MAP connected is 35 degrees degrees (density altitude apparently irrelevant in this case since max advance for engines timed for 20 degrees BTDC is limited to 35 degrees). So in short, the timing should nominally have been 24 and 35 degrees but was measured at 18 and 30.
We then rotated the crank sensor as far as the slots allowed, and this brought the firing up to spec (23/35). RPM drop is now 150 (Plasma OFF) and 50 (mag OFF). Nevertheless, the engine just doesn't feel as smooth as I believe it was during the first few hours, and I know from combing the archives here researching this problem that many with LSE Plasmas see no or negligible RPM drop mag OFF (although as noted above, I have a three-blade Catto, so less rotational mass compared to a metal prop).
I spoke with Klaus and he said to check fuel flow at idle, MAP at idle, and mag timing; if those were OK then the only thing left was to send the unit in, although he said CDI degradation drifts to advanced, not retarded, timing. I have done the first two and they seem normal (2-2.5 gph, 10.5-11.5 inHg). I have not checked mag timing since I need to give my helper a respite from my daily requests for assistance, and I wonder if there aren't other things I've overlooked that I could address first.
As a final note, the plugs all look relatively clean though a bit oily (engine seems to still be breaking in), the MAP lines and induction tubes have been thoroughly checked for leaks, and all wiring and connectors for the system have been inspected and appear fine.
So, I'm stumped. Any ideas?
Thanks,
Eric
