rvmills
Well Known Member
I've been going through a troubleshooting process to determine the cause and then try to fix a large RPM drop when running on only my LSE Plasma I EI (ie, when turning off the mag during run-up checks).
This thread http://www.vansairforce.com/community/showthread.php?t=44564 caught my eye, and is about a very similar drop with a Plasma III, but discusses PII vs. PIII performance, so thought I would post this separately so as not to clutter that thread. It may help others (like Bruce, the OP in that thread) with the troubleshooting process, though I will have to say, I'm not sure I've found the smoking gun yet (though it's working as of today...fingers conservatively crossed).
A little background: RV-6, IO-540, bought flying with 1 mag and 1 Plasma I. TT at purchase 455 (with a trouble-free LSE EI), TT now, 580. Last year at about 520 hrs I had a coil go bad, which manifested itself in a 200 RPM mag drop. Turned out the coil actually went "half bad", which Klaus told me could happen given the symtoms (only one spark plug in a pair not sparking). So I replaced the coil, and all was well. Klaus recommended I replace all three coils, given the age and time in service, but I opted to hold out, as I was buying avionics for a panel upgrade.
Last fall, after the panel upgrade and 5 months hangar queen time, I started experiencing a similar drop. First thought was, "well dummy, you should have listened to Klaus and should have replaced all three coils". Easy fix though, right...two more new coils, and voila...nope, ooops, same problem, and the beginning of my lessons in really troubleshooting a Plasma LSE. (And FWIW, I've found that if you do your homework and the recommended troubleshooting, Klaus is great to work with and very helpful. If you call up uninformed & looking to be schooled, he's a bit more...well, direct...AMHIK ).
So after replacing the coils, I then replaced the old hi-tension spark plug leads with new leads...no change. Replaced all the spark plugs with iridium plugs...no change. Tested the the old RG-58 cables from the brain box to the coils (should show open when disconnected at both ends, and did). But I went ahead and replaced them with RG-400 (as recommended) with new BNC's (brain-box end) and spade fittings (coil end)...no change. Tested the resistance between the appropriate DB-25 pins and the trigger coils. All checked good for the recommended 500+/- ohms, even when wiggling the wires and the coils. Didn't change the trigger coils, as it's a prop removal with my old-style trigger coils, and they checked out OK.
Next I went out and picked up a timing light and set out to check the timing and then take EGT readings to help diagnose. Timing seemed all over the place, so I sent the box back to Klaus for a bench check. Bench check went fine, but Klaus updated some of the internal components for me while it was in, just to have the latest and greatest innards. Box back and installed, and geez, no change! Arrrg.
Went back to taking EGT readings, and during that process, the mysterious RPM drop went away. Talked to Klaus, and it was possible that a plug had become "wet" during all the run-ups and drop-checks, and then dried out during the extended EGT-reading run. Checked the plugs, all good. Did some test flying, with consistently good run-up mag checks before and after flying.
Lasted that way till last week (about 60 hours of flying), and the bad drop came back, but on an intermittant basis (my favorite kind of glitch). It would drop sometimes, and then "right" itself during the run-up. Sometimes back and forth. So no flying, and back to the troubleshooting routine. Swapped coils, swapped wires, swapped plugs...still intermittent, and still in the same pair of cylinders (3/4). Thought it might be heat (seemed better when hot), thought it might be RPM (seemed better when higher), but no rhyme or reason appeared, and those ideas failed to be repeatable.
Re-checked the firing coil wires and the trigger coil wires, all checked good, and then cleaned and re-set all the connections, but no change. Even re-secured the spark plug wires, making sure they weren't laying on each other anywhere along the runs. Basically, I've changed everything in the system except the trigger coils and the brain box. To change both is about an $1100 fix (to upgrade to a II or III box and the new-style crank sensor). Not much different than a new pair of mags and harnesses...hmmm.
One of the things I noted in the troubleshooting guide was to ensure that the three low voltage trigger coil wires were routed away from all high voltage wires. Mine were bundled with the EGT and CHT probe wires (also low-v), as well as the wires to the alternator. So I separated them, and wrapped the coil wires separately, tidied up all the wire bundles and made sure all the connections were clean and solid (again). Expected it to remain the same, and figured if it did, I'd send the box back, and if it checked good again, it's off with the prop and replace the trigger coils.
Then, as I re-mounted the box under the panel today, I noticed some drops of hydraulic fluid on a nearby fitting. Just before this LSE issue (re)started, I replaced the brake fittings on the cylinders, and had one line pop out of it's fitting on test. Thought I had cleaned up all the mess, but obviously missed the spots that required getting upside down under the panel to see. Just above where I saw the drops was the brain box, and with the BNC's off, I could see a small ring of hydraulic fluid around the base of the male BNC of, you guessed it, the connector for the channel to #3/4 cylinders. The inside of both connectors looked good, but I cleaned them carefully and blew them out with air, just in case, and reconnected all.
Still not too hopeful, and ready to pack up the box, I went out and ran it up. No drop...nada...standard LSE-only purrr with the mag off. Ran it for a while, cycling through the EGTs on my VM-1000 and taking several readings, while checking several times for a drop that never happened. Couldn't make it happen if I tried.
Pylon Racing School here at Stead, and then wx prevented me from local test-flying, but that is to follow, before I claim victory. Could be the hyd fluid. Could be the wire reroute. Could be the take it all apart and put it back together carefully factor, or a combination of the above; Could also be a gremlin just waiting to come back (not so naive as to ignore that!) but I'll be watching it closely, as I don't like "too good to be true" fixes, and really dislike intermittent and "could not duplicate" gripes.
Will post if it comes back and I either find a fix or get a new box or a pair of mags, but if this helps someone troubleshoot an LSE issue, all the better. Klaus' TS guide on his site is pretty good, and he spent some good time on the phone with me as I ran through it. Bruce (from that other thread), I hope your #3/4 drop is just a coil, but if not, maybe some of the above troubleshooting steps may help you find the bogey!
Oh yeah, and if you blow a brake line, look for that nasty stuff everywhere!
Cheers,
Bob
This thread http://www.vansairforce.com/community/showthread.php?t=44564 caught my eye, and is about a very similar drop with a Plasma III, but discusses PII vs. PIII performance, so thought I would post this separately so as not to clutter that thread. It may help others (like Bruce, the OP in that thread) with the troubleshooting process, though I will have to say, I'm not sure I've found the smoking gun yet (though it's working as of today...fingers conservatively crossed).
A little background: RV-6, IO-540, bought flying with 1 mag and 1 Plasma I. TT at purchase 455 (with a trouble-free LSE EI), TT now, 580. Last year at about 520 hrs I had a coil go bad, which manifested itself in a 200 RPM mag drop. Turned out the coil actually went "half bad", which Klaus told me could happen given the symtoms (only one spark plug in a pair not sparking). So I replaced the coil, and all was well. Klaus recommended I replace all three coils, given the age and time in service, but I opted to hold out, as I was buying avionics for a panel upgrade.
Last fall, after the panel upgrade and 5 months hangar queen time, I started experiencing a similar drop. First thought was, "well dummy, you should have listened to Klaus and should have replaced all three coils". Easy fix though, right...two more new coils, and voila...nope, ooops, same problem, and the beginning of my lessons in really troubleshooting a Plasma LSE. (And FWIW, I've found that if you do your homework and the recommended troubleshooting, Klaus is great to work with and very helpful. If you call up uninformed & looking to be schooled, he's a bit more...well, direct...AMHIK ).
So after replacing the coils, I then replaced the old hi-tension spark plug leads with new leads...no change. Replaced all the spark plugs with iridium plugs...no change. Tested the the old RG-58 cables from the brain box to the coils (should show open when disconnected at both ends, and did). But I went ahead and replaced them with RG-400 (as recommended) with new BNC's (brain-box end) and spade fittings (coil end)...no change. Tested the resistance between the appropriate DB-25 pins and the trigger coils. All checked good for the recommended 500+/- ohms, even when wiggling the wires and the coils. Didn't change the trigger coils, as it's a prop removal with my old-style trigger coils, and they checked out OK.
Next I went out and picked up a timing light and set out to check the timing and then take EGT readings to help diagnose. Timing seemed all over the place, so I sent the box back to Klaus for a bench check. Bench check went fine, but Klaus updated some of the internal components for me while it was in, just to have the latest and greatest innards. Box back and installed, and geez, no change! Arrrg.
Went back to taking EGT readings, and during that process, the mysterious RPM drop went away. Talked to Klaus, and it was possible that a plug had become "wet" during all the run-ups and drop-checks, and then dried out during the extended EGT-reading run. Checked the plugs, all good. Did some test flying, with consistently good run-up mag checks before and after flying.
Lasted that way till last week (about 60 hours of flying), and the bad drop came back, but on an intermittant basis (my favorite kind of glitch). It would drop sometimes, and then "right" itself during the run-up. Sometimes back and forth. So no flying, and back to the troubleshooting routine. Swapped coils, swapped wires, swapped plugs...still intermittent, and still in the same pair of cylinders (3/4). Thought it might be heat (seemed better when hot), thought it might be RPM (seemed better when higher), but no rhyme or reason appeared, and those ideas failed to be repeatable.
Re-checked the firing coil wires and the trigger coil wires, all checked good, and then cleaned and re-set all the connections, but no change. Even re-secured the spark plug wires, making sure they weren't laying on each other anywhere along the runs. Basically, I've changed everything in the system except the trigger coils and the brain box. To change both is about an $1100 fix (to upgrade to a II or III box and the new-style crank sensor). Not much different than a new pair of mags and harnesses...hmmm.
One of the things I noted in the troubleshooting guide was to ensure that the three low voltage trigger coil wires were routed away from all high voltage wires. Mine were bundled with the EGT and CHT probe wires (also low-v), as well as the wires to the alternator. So I separated them, and wrapped the coil wires separately, tidied up all the wire bundles and made sure all the connections were clean and solid (again). Expected it to remain the same, and figured if it did, I'd send the box back, and if it checked good again, it's off with the prop and replace the trigger coils.
Then, as I re-mounted the box under the panel today, I noticed some drops of hydraulic fluid on a nearby fitting. Just before this LSE issue (re)started, I replaced the brake fittings on the cylinders, and had one line pop out of it's fitting on test. Thought I had cleaned up all the mess, but obviously missed the spots that required getting upside down under the panel to see. Just above where I saw the drops was the brain box, and with the BNC's off, I could see a small ring of hydraulic fluid around the base of the male BNC of, you guessed it, the connector for the channel to #3/4 cylinders. The inside of both connectors looked good, but I cleaned them carefully and blew them out with air, just in case, and reconnected all.
Still not too hopeful, and ready to pack up the box, I went out and ran it up. No drop...nada...standard LSE-only purrr with the mag off. Ran it for a while, cycling through the EGTs on my VM-1000 and taking several readings, while checking several times for a drop that never happened. Couldn't make it happen if I tried.
Pylon Racing School here at Stead, and then wx prevented me from local test-flying, but that is to follow, before I claim victory. Could be the hyd fluid. Could be the wire reroute. Could be the take it all apart and put it back together carefully factor, or a combination of the above; Could also be a gremlin just waiting to come back (not so naive as to ignore that!) but I'll be watching it closely, as I don't like "too good to be true" fixes, and really dislike intermittent and "could not duplicate" gripes.
Will post if it comes back and I either find a fix or get a new box or a pair of mags, but if this helps someone troubleshoot an LSE issue, all the better. Klaus' TS guide on his site is pretty good, and he spent some good time on the phone with me as I ran through it. Bruce (from that other thread), I hope your #3/4 drop is just a coil, but if not, maybe some of the above troubleshooting steps may help you find the bogey!
Oh yeah, and if you blow a brake line, look for that nasty stuff everywhere!
Cheers,
Bob
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