So close to Megasquirt! 3 questions before she runs
 

I am finally starting my 1991 1.6 turbo project, and I have everything I need to get the car running on Megasquirt PNP2. Just 3 questions-

1. I have the AEM AFR gauge. Clearly, red is 12v and black is ground. Brown and White are both 5v output but one is positive and one is negative. I know one of them is supposed to be spliced into the factory O2 sensor harness, I just don't know which one. I know one of them is supposed to be grounded "to the same ground as the ECU", but where would that ground be?

2. I am having a terrible time trying to find a laptop with a serial connection for tuning. Can I simply get a serial to USB adapter? Some say that creates "data losses in format transfer" and others say it's totally fine. I'd like your opinions.

3. I am going to yank the fuel pump relay and crank it with a timing light before letting it run just in case timing is dangerously off. Is there anything else I should be prepared for/do for first startup?

Thanks so much

1. Check the user manual. Not sure exactly which AEM wideband you are using but the manual will tell you what each wire does. I think usually the brown and white wires are 0-5V linear output and narrowband simulation.

2. Serial connectors on laptops are a thing of the distant past. A USB to serial adapter is fine but not all use the same chipset. Some do not work with the microsquirt module which is what your PNP2 uses. FTDI and a few others work. I think it's the CH340 ones to avoid.

3. I would check all the sensor inputs and make sure they're reading correctly before starting. Read over the MSPNP manual to make sure you've covered everything. I believe you will also need to remove the ST SIGN 10A fuse the the MSPNP2.

1) hey I’m assuming you’re using the AEM X Series wideband. I’m using the same wideband. I joined the brown and black wires together and connected them to the group of ground wires on the back of the head on the passenger side. So far I’ve had zero issues running it that way. As for the white wire you have 2 options: A) cut the old connector of your stock o2 sensor and attach that to the white wire and plug it into the red/blue wire that runs to your ecu. B) cut the connector off the red/blue wire and just splice that wire and the white wire together. Option A is more easily reversible if you ever wanted to return the car to stock.

2) cranking it over without the fuel pump relay is fine but honestly if your timing was in spec before the megasquirt install then I’d say you’re fine. Just follow the directions on how to verify that the timing displayed in MS matches your crank. You basically need to set timing to fixed 10* then check your timing with the timing light and see if it’s at 10* or something else. If it’s something else you need to adjust your trigger angle or whatever. I have SpeedyEFI and don’t have the trigger angle adjustment I just manual moved my CAS to match what I had my timing fixed to.

My car was a shit show and I was only off 2* for the record so don’t be too worried about that.

After you verify the fixed timing make sure you turn fixed timing off, check what your idle timing is set at again and recheck timing with timing light to double check that what MS is commanding for timing is the same that your getting at the crank. Then you’re 100% good to go!

My biggest mistakes was not fully prepping for the tuning process. I highly suggest watching OGPedXing on YouTube before even making a single change or firing up your car. His tuning series is top notch if you have no idea what you’re doing.