Megasquirt install questions
 

I am finally going to get around to installing my reverant eMS2 this weekend and I have a few questions that I need to clear up before I dive in. Keep in mind that, if any of this sounds simple or comes across as ignorant it is because when it comes to wiring and such, I am ignorant and still tying to learn.

1. I am going to use Add-A-Circuit to get switched power from the fuse box underneath the dash. My question is if I can run both my electronic boost/wideband gauge and my LC-1 off of one of these things or if I will need two?

2. Which fuses on that box are switched power?

3. For the GM boost solenoid am I able to wire it to the stock boost solenoid connection for my MSM or will I have to run one of the wires all the way to the MS under the dash somehow? (I assume reverant will have to answer this one because I am not sure how he set up the harness that came with the unit.)

4. What is the best grounding point that I can use under the dash?

5. I plan to use the internal boost sensor in the MS to send a signal to my boost gauge. Rev provided two blank output wires on the MS harness. How do I program this output to send the boost reading to the gauge?

Thanks in advance to anyone that can offer any answers or advice.

1) Yes.
2) Engine
3) Use any 12V switched power source from the engine bay for one of the two wires of the solenoid; the other wire goes to the green wire on the MS harness.
4) The ECU wiring.
5) That's not what the "output" wires do. These are on/off outputs, ie they can switch a relay on or off, thats it. I'm not aware of any ECU that does what you want. You will need to tap into the MAP sensor inside the MS to share the vacuum/boost signal.

Thank you very much for the response. I assume by "yes" you mean I can run both items from the same switched power source. Are the grounding wires I need to use from the ECU wiring also black or some other color?

You can use the black wires on the top connector of the ECU, pins 20-24.

And you can put a tee in the vacuum line going to the MS and run that to a mechanical boost gauge or plumb your sending unit for an electrical gauge into it.

I am not gonna switch to a mechanical boost gauge for two reasons. The first is I already have the electronic gauge. The second reason is because it is both a wideband and boost gauge and will take up less space that way.

I am not sure I understand the second part you posted. Are you referring to what Rev said about connecting the wire from the gauge to the sensor inside the MS or are you talking about something else.

I was saying just re-use the sender from your gauge for your gauge.

That electronic gauge is going to be calibrated to expect a signal from the sensor which it came with, which is quite probably different from the calibration used by the sensor inside the MS. Thus, you are going to need to do what Sixshooter said: use the sensor that came with the boost gauge to drive the boost gauge.


Also, as an aside:

When you tap into an analog signal line and branch it out to another device, you increase the likelihood of introducing noise into the line.

For lines carrying non-critical signals which are not sensitive to minute changes in amplitude (such as the IAT and CLT lines), this is not a big deal.

For lines carrying critical signals which ARE sensitive to minute changes in amplitude (such as MAP and O2), this is an Extremely Bad Idea™.

In other words, even if the calibration did match, tapping into the MAP sensor inside your MS and bringing it out to a boost gauge located some distance away and at a different ground potential brings with it the possibility of introducing noise into the MAP line which will negatively impact the performance of the MS itself.

It did not come with its own sensor because I did not order one. I assumed I could tap into the one for the MS. So do I need to order one? I'm not fond of opening up the MS.

Yes.

What gauge are you using?

Vei systems dual monitor wideband/boost gauge.

Site: veisystems.com
i would give you a real link bit I am on my phone.

Huh. They don't seem to give any specs whatsoever on the sensor calibration for the boost/vac side. They just tell you to buy the SEN-P70B sensor, which for $39 is precisely what I'd do.

Ok, that is what I will do. Thank you for the information.