I've been slowly building my megasquirt over the past month or so. I'm not sure if anyone cares but I'd like to share some of my problems and solutions.
First problem was I installed Q4 then decided to remove it to do the idle mod and somehow damaged the contacts. After trying to clean and fix the contacts I ended up using the mega manual to figure out how to wire around Q4. So far everything looks and tests ok.
Next it was time to hook up the stim and power up megasquirt. Flip the switch on the power supply and no lights.
Got out the meter and started testing for voltage. Stim had 12+ volts, Pin closest to DB9 of U5 have 12+, middle pin had less than 1 Ohm to ground, and last pin had....12+ volts. Hmm. I started to read the mega manual again and it says C22 could be backwards. looking at my board i noticed that C22 is not even there. WTF, I was pretty sure I had everything but I dug though the extra parts and there it was in the little bag labeled C22.
So I install that and try to power it up again. Still nothing. Voltage at the last pin of U5 is still about 12 volts. Next thing the mega manual says "It's also possible that one of the diodes is backwards" Great, am I really this retarded? Sure enough I found D10 was installed wrong. I removed the diode and checked it with a meter before putting it back in. This time when I went to power it up i got lights! Even U5 had 5 volts.
Last problem, I can flash 1760 lines of the firmware but when I open Megatune I get "controller code not match signature" After checking checking my connections, reflashing firmware, and reinstalling megatune, I found that my usb to serial adapter was crap. A cheap ebay $2.50 (shipped) serial cable solved that problem.
Sorry for the long post. I just wanted to share this info because I thought maybe it could help someone. Also the search button is awesome. I got all this sorted out and didn't have to post once!