8-19-03  /  8 hours  /  1349 total

I went to the airport this afternoon, and tested the vacuum/pressure gauges.  With 15 psi on the Mityvac, the Boost gauge in the plane reads 17, and the Sears automotive test gauge reads 14.5.  5 psi of pressure reads just that on all the gauges.  Yesterday, I had the Sears gauge on one vacuum port, and the boost gauge on the other.  It’s clear now that my 2-3 difference between ports, was actually between gauges, and the ports are the same (as they should be).  I went ahead and T-ed them together anyway. 

First the tach- I started by adding enough wire for about 30 more wraps (34 total) around the plug wire.  This read exactly double of the real RPM.  I removed 10 wraps (24 total), and still double.  Put copper tape around tach signal wire, still double.  Removed 10 more (14 total)- reads OK low, but wanders at higher rpm.  Removed 5 wraps (9 total)- still OK low, and wandering high.  Removed all the extra wire that I added, left 4 turns of the original wire, and wrapped copper tape around the signal wire.  I also clipped a ground wire to the tape, and to the airframe.  This seems to work.  Of course there wasn’t enough direct sun to even attempt to use my optical tach, but the rpm increased and decreased very consistently, so it certainly appears to be working. 

As for the controller and tuning- I started the day with controller A still working fairly well.  Idle is currently 1400 rpm, and the boost gauge reads 16 in of vacuum, which we now suspect is really 14 inches of vacuum, or 16” MAP.  As you can see, this is mighty close to the 15” MAP transition point.  It’s not surprising that sometimes idle seems to be above, below, or in the middle of the transition point. 

I tried using the mityvac to suck the MAP to the controller down to a point where it would be below the normal engine operating range.  This would have provided plenty of amusement for anyone watching, as I tried to jockey the mixture knob to keep the confused and unhappy engine running.  Gave up on this.  Next, I tried something that Tracy had mentioned (not to be confused with “recommended” <G>).  I set the controller on mode 7, ran up the throttle, then closed it suddenly.  When the vacuum sucked down to 20 inches, I hit the button (the one with the invisible light).  This worked just fine, and the engine runs OK with all 4 injectors at idle.  I had one controller set up normally, and the other with the transition at 20 inches, and could tell that the normal controller had a slightly more even idle.  Mind you, it wasn’t that significant, but clearly there was a difference.  With this in mind, I filed this idea away as a last resort. 

Next, I tried some calibration, and kept running into problems at around idle, so I decided that I needed to move the transition point away from idle by a couple inches of vacuum.  Since Bruce’s porting job left me with an idle vacuum of 16” MAP, I decided to set the transition to 2 inches above idle.  This put me at 18” MAP, rather than 15” that comes standard.  THIS WAS THE KEY! 

Once I changed the transition point to 18”, I was able to tune both controllers, and everything worked as expected.  I can’t even feel the transition point now, so there must be plenty of range in the EC-2 to accommodate the sub-spec MSD injectors.  I can operate the engine from idle, to full throttle (3psi boost), and back to idle without anything terrible happening.  This is good enough to fly!

Now that my tach seems to be working, it appears that I get 4550 rpm at 30” MAP, and 4750 rpm at 36” map (3 psi).  This is just a wee bit lower than I’d like to see it, though certainly enough power for the RV-3.  I still have to decide if I want to repitch the prop a bit for something closer to 5500 rpm at sea level power.

I’ll probably try the new MSD injectors that I ordered, and see if they seem closer than the ones that I have to the stock Mazda 550’s.  Either way, I’ll eventually send the current injectors to have them tested, along with the 4 stock Mazda 550’s that I have left. 

Aside from these issues, my transponder will be certified Friday, and the chute will have returned from repack.  I’ll be getting an hour or so in a friend’s RV-8, so Sat afternoon, or Sun could be go for first flight.