Background: I've got an MS1v3 set up to run parallel on my '97 Miata.
I've modified it in the following ways:
- Joe Perez's "better/inverted spark circuit"
- IAC2A connected to JS11 (with an inline diode) for launch control
- Extra MAP sensor installed and signal to JS5 for constant baro
- SPR4 connected to JS4 for EGT logging (signal comes in to MegaSquirt from an external circuit board made by SymTech Labs)
The unit is also modified in that it's got a USB-serial connector installed (thanks to the previous owner: arkmage), but I don't think that's likely to affect what I'm trying to deal with at the moment.
When I first hooked up the thermocouple, I noticed that EGT readings on MS1 seemed unaffected by actual EGT, so after doing some testing I've discovered that somehow I'm getting signal bleed-over between JS4 and JS5. With the MS hooked up to a stim and the EGT signal disconnected, I can blow into or create vacuum on the baro sensor and watch EGT readings go up and down.
Any ideas how I've screwed things up so much? I've included links to photos of my board.
In this first image, I had removed the jumper from the proto area (just used to bring the jumper to SPR4 through to the other side of the board) to JS4. But normally it would be connected.
Any suggestions/troubleshooting tips are appreciated. Any namecalling/insults are not appreciated but will be tolerated, especially if you can help my fix this.
Oh yeah, and when I try to measure resistance between JS4 and JS5 with my digital multimeter--with the MS1 unit powered down--I get the following results:
When measuring between JS4 and JS5 with COM lead on JS5:
- 1.06M diminishing to 1.02M ohms when testing in the 2Mohm range
- 175K diminishing to 170K when testing in the 200Kohm range
When measuring between JS4 and JS5 with COM lead on JS4:
- ~0.73M (possibly diminishing, but slowly) when testing in the 2Mohm range
- 127K diminishing to 126.3K when testing in the 200K range