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Old 04-03-2018, 09:51 PM
crabandy crabandy is offline
Join Date: Jan 2010
Location: Ottawa, Ks
Posts: 1,990

So my 20 hours of flight time playing with timing using 23-25 BTDC for normal flight ops gave me consistenly lower CHT's on climbout, but inconclusive results overall with advance at lower manifold pressure settings. More on that later...

I removed my ECU's and sent them to Ross at SDS for a new software flash for the LOP switch functionality. While waiting for my ECU's I added 1 wire to each ECU connector joined at a switch to provide 12 volts for the LOP function.
I put a lot of thought into making the LOP switch fit my normal checklist/cockpit flow, I put the switch next to the fuel pump/throttle where it seemed to flow the best.

I'm lucky my local awards/trophy shop is easy to deal with, they were able to make a panel sticker for my new switch to match the other stickers.

If starting over I would probably place it right next to the mixture, but it does stand out a little bit and is next to the throttle/mixture. I had thought about putting the LOP switch by the ignition switches, but I tend to ignore that side of the switch quadrant as the master/ebus/alts/ignitions are always on, I think this spot ties it more to throttle/mixture settings as it should be.

I had never verified the timing pickup magnets in the flywheel, Robert from EFII had drilled and installed them on my original installation. Referencing the SDS instructions and Lycoming service instruction 1437, I needed to make a 10 degree mark on the back of the ring gear and make a pointer denoting the case split.
I used a cloth tape measure to measure halfway between TDC and 20 on the ring gear and made a mark. The Lycoming tool looks like it just squares off the ring gear so I did the same with my carpenters square and measured back to the case split and drew a line on my plenum and made a pointer from an old hacksaw blade.

I set up the timing light, chocked the airplane and it was almost easier than checking the timing on a car engine. Not sure why I never verified prior, but my position/ timing was correct. I verified by changing the magnet position programmed on the ECU's.

I input my RPM timing and manifold pressure retard/advance schedule and did a series of runups. I only have 1 programmer so I can only view/interact with 1 ignition on the fly. I tend to leave the programmer on my 88 ECU as it is wired to the battery bus and I don't have to turn anything else on to play with programming. Everything seemed well with the ignitions and a quick glance at the programmer showed my expected timing of 23 degrees (25 BTDC via RPM and 2 degrees of retard at 29 inches manifold pressure) upon full power for the takeoff roll. When I leveled off at 3000 AGL and pulled power I didn't see the expected advance as manifold pressure was reduced. My LOP switch did not apply the programmed 7 degrees of advance either.

Back on the ground I found my 71 ECU was performing as programmed, It was late Friday evening and I put it away sent a couple of emails and pondered the problem. A couple of days, a discussion with Ross and a little more trouble shooting found a bad manifold pressure sensor. My system has a separate manifold pressure sensor for each ECU, easy to swap sensors and verify the bad sensor. My manifold pressure sensor failed "high" as in it was always reading 30.1. I picked up a replacement at NAPA, it was a stock GM/ Delphi sensor.

Makes me wonder how long the sensor has been bad, I should have caught it as soon as I started using the programmer. I am a slow learner and learn by doing (making mistakes).... But I spent most my time in the RPM/manifold pressure setting windows and only more recently using the gauge pages of the programmer that show ignition timing/manifold pressure/RPM. Could've been dead from installation, with the proper timing curve its very hard to tell anything is amiss when the engine is happily purring along.

Why didn't my LOP switch work?
There is a hidden setup menu in the SDS ECU's, one of these settings voids the LOP switch above 25.1 inches manifold pressure. Nice little safety feature for sensor or Pilot failure.

I'm looking forward to more flying and hopefully more definitive results with my timing.
RV 7 300 hours and counting
12/17 donation

Last edited by crabandy : 04-03-2018 at 09:58 PM.
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