Well, looks like Im going to be inlisting in your guys' help for this again. Whats funny is, this time Im doing it the easy way, piggyback installation (for a friend) and it actually seems harder for me because I keep thinking of the way I did it, going for stand alone. So allow me to bounce some thoughts off of you, and retort back if this is correct or not:

This install will only be fuel for now. Later it will be spark and fuel, Stock ECU will still be in place.

The stock ECU should control:
Tach
Speedo
Cruise
Fuel Pump/ASD
IAC
Rad Fans
Spark (until I hook MS up to it)

Meaning, I shouldnt need to use the wires from the MS on those, right?

Since the stock ECU is still going to be controlling spark for now, I would need to Splice in the temp sensors, instead of cutting and making a new harness like I did last time. Can the stock sensors share a connection with MS and PCM, or will I need to actually get the GM IAT and CLT sensors and connect those to the MS?

Currently, this vehicle has no WBo2, in fact he was talking about getting a NB02 (I advised against this). Should I just tie the pink o2 wire from MS into the oxygen sensor signal wire, and set it up appropriately in the settings?

I think thats it for now, But Im sure Ill have more later. Thanks in advance.

You have it for the most part. I personally would use the MS to control the fuel pump relay. As far as the sensors go, you can use the stock 420a sensors if you are using MS2/E code as you can set the temperature curve and resistance values. As far as I know MS1/Extra code needs the GM sensors. Tuning will be difficult with a narrowband O2 sensor. If your friend wants to go this route then you can send the signal to the MS unit as you described. He will not be able to dial the tune in very well though using this method.

So just to be clear, can I use one IAT and CLT and tap into the signal for MS, or do I need to get another set of temp sensors dedicated to the MS unit?

Well, are you using an MSII or MSI? I spelled it out in my first reply.

Its MS2/E. I was just making sure because I remember someone posting a few times that you need separate sensors for the MS, but it was at the end of a thread and no one verified. On my car I just cut the sensor wires and hooked ms signal and ground right up to it, and changed the resistance values in TunerStudios. Just making sure I can just tap in before I go hacking up someones wiring harness.

Thanks for the replies.

Originally posted by 740 turbo brick
So just to be clear, can I use one IAT and CLT and tap into the signal for MS, or do I need to get another set of temp sensors dedicated to the MS unit?

Unfortunately you need dedicated sensors. The stock PCM uses multiple bias resistors, which the MegaSquirt ECU can't handle (not necessarily a good or a bad thing, it's just how it is).

If you have an MS2 ECU, the second set of sensors can be 420A/Chrysler sensors or GM sensors; they're both just as easy to calibrate in TunerStudio MS.

Ok, got 2 sets of sensors hooked up and working, car is running on MS fuel/ECU spark. Im having a problem now though. VERY erratic TPS signal, I have to re calibrate it every time the car is shut off. It will be off by 5% or more each time. While its running the TPS will be going crazy. Im wondering if this is because the TPS V Ref is not hooked up? I figured the stock ECU power would be fine, unless the MS needs to power the TPS itself.

Also, while running the Sync light in the corner will randomly say not synched, like its being disconnected, and the tach will spike showing the same. I have the Crank signal wire soldered to the IGN wire, and all the grounds soldered to a terminal and grounded. Just to be sure, they were grounded to the firewall, but I moved them to the negative terminal. Any thoughts?

To add to this, I watched the lost sync counter gauge. It went from 90 to 125 while WOT at 5k RPM. It wouldnt Rev any further past 5k even wide open. Also, the Duty cycles are jumping all over the place, and smoothing/changing VE isnt making the car run any better. Somethings up here...

Bump for help