Sorry.... I sort of left this topic hanging.
As you know, the car ran pretty bad when it snorkeled full strength hot air. The air/fuel mixture was all over the charts but mostly the car was running alarmingly lean. ... or so I thought.
The hot air upset the volumetric efficiency in a negative way, so the Megasquirt was set up to automatically adjust the air/fuel and try to maintain the target ratio. This is when I discovered Megasquirt and the wideband controller were reporting two different air/fuel ratios.
After several evenings of investigation, part of the mystery was solved. Apparently the spark plug wires were throwing off a bunch of EMF and the stray energy was being absorbed by the air intake temperature sensor harness. This "noise" was causing havoc with the megasquirt.
So this hot air experiment more or less got put on the back burner while the megasquirt gets sorted out. The megasquirt still has an offset that I can calibrate out, however there is also a slight signal drift that has me baffled. I think I may have broken my Megasquirt or my harness has some major issues..
The car still runs fine and the Megasquirt continues to more or less "work" but it wont lock in on the target air/fuel ratios in my setup tables. Something is definitely broken because the gas mileage is hovering in the 40ish neighborhood. While the MPG is awesome for most cars, it sucks for this car.
Trying to determine if the wideband or the megasquirt was at fault is nearly impossible with the engine running. Eventually I had to do a bit of rewiring so i could safely inject a known voltage and read it back on both devices. When I injected a steady 2.4 volts DC into the system, both the wideband and the megasquirt reported 14.60 AFR. This is encouraging . The problem only presents itself when the engine is running. Automotive electrical systems are known to be "noisy" and I'm picking up a lot of ignition noise on the battery circuits. I added a bunch of capacitors here and there to sort of filter the junk but the problem remains.
I typically troubleshoot a problem until it's fixed.... however this time I said berkeley it. I'll figure it out on the dyno. The dyno electrical system is simple and clean. The dyno is still a few weeks away from being 100% functional, but preliminary findings indicate the megasquirt is still acting goofy.
So... this project is still going 110% full speed ahead, but um unless you stand back and look at the big picture... it doesn't seem like much is going on. I'm relying on the dyno to sort out zillions of minor issues that have cropped up and new issues that are going to crop up. The car plus the dyno is a massive project but I am so close to getting results.
Eventually the hot air project will make its way back to the front line.... if it works on the dyno. Snorkeling 100% hot air ain't going to work, I can tell you that much. A compromise has to be made.... We will find out soon enough.
My highspeed internet modem is on the fritzes. I only get internet in five min chunks before I have to kick the modem off line. I'm going to try and upload this post, but the formatting may be a bit off.
Oscilloscope was picking up a classic ignition "flyback" signal from with the probe attached to nothing. That is a significant amount of energy .
Some more electrical noise on the 12V DC circuits. I don't recall if this is after the ignition was fixed.
El'cheapo spark plug wires were fabricated to try and reduce the EMF under the hood. These temporary wires worked but the problem was not 100% solved.
a bit of re-wiring and I was able to inject 2.4 VDC into the megasquirt and the wideband gauge.
Megasquirt reports the correct AFR with the injected voltage.
Gauge agrees with megasquirt ... as long as the engine is not running.
Stay tuned!