MSefi.com read only forum (Jan.15,2018)

I've got my head wrapped around most of the wiring for the megasquirt as I've done a ton of research before thinking about actually buying the unit (MS I v3 or maybe 2.2), but there are two things that I still can't quite understand. Well, since i'm only looking to control fuel for now, that only leaves one thing. This would be the tach/crank position input. I have a 1997 Chrysler Cirrus with the 2.5L Mitsubishi/Chrysler engine which is extremely similar to the 3.0 6g72 from the Eclipse.

However, the crank sensors differ. The one from the 2.5L is driven from reading little notches in the flexplate whereas the one from the 3.0L is driven off reading the crankshaft in the "front" of the engine. As I understand it, the 2.5L uses a hall effect sensor since it has "a metal shutter wheel, which has small evenly-spaced windows." Am I correct? Also, would the 3.0 use the VR sensor since it is reading the crank (i'm assuming the crank has magnets in it)?

2.5 Crank Position Sensor and Flexplate

Well, regardless, both of these setups confused me by flipping back and forth between the FSMs and the megasquirt wiring diagram. The MS wiring diagram shows a + and a - for hooking up the tach/crank position input. However, for sake of simplicity let's just take the 2.5L, there's an 8v supply coming from the ecm, going to it (the crank sensor) and ending up at the distributor. Then it has a sensor ground and finally we have the crankshaft sensor signal going straight to the ECM. I'm guessing that the only two wires i'd need (considering that i'm only going to be running fuel) are the crankshaft sensor signal going to pin 24 and the sensor ground going to pin 2 on the MS? So, would I just let the ECM supply it with 8v or am I missing something here?

On the other hand, we have the 3.0L sensor. I'm not really going to need to run this, but just for reference i'd like to know how this would be wired in if I were to chose this route. It has a 12v wire going to a relay, a black going to ground, and 5v coming from the ECM. This seems much more different than the 2.5's. Is the 3.0's crank sensor getting a switched 12v source, going to a sensor ground, and sending 5v to the ECM? I'm not too sure how the sending of the signal is working. The wiring diagram makes it look like the ECM is sending the sensor the 5v, but then it's also getting 12v from the relay. Very confusing.

3.0 Crank Sensor wiring diagram

Well, I guess what i'm trying to ask, is how would I wire up the 2.5's crank input to the MS? I'm thinking of leaving the 8v wire as-is, splicing the sensor ground and sending it to the MS, and splicing the crankshaft sensor signal and sending that to the MS too. Might I be missing something here? Also, I saw that the 2.2v of the megasquirt I connects to the negative side of the coil instead of a crank sensor. Could I just grab the negative side of the coil (i'm guessing this is the dark green wire coming from the "generator/coil?") and wire it straight to pin 24 to achieve the same thing as the crank sensor?


Thanks in advance, I really appreciate it.

I've drawn up a tentative set of settings that may work for this engine - see this thread:

viewtopic.php?f=89&t=34278&p=209027&hil ... er#p209027

However, I'm not sure if they have been tested yet.

Many thanks Matt, bookmarked and saved in the file archives. However, I still question how one might wire up the sensor to the MS? I can't really go off the 3.0 article you linked in that thread, because that's for the older 88(or was it 89...?)-94 3.0's which vary significantly from the later 95-00 2.5/3.0's. Those year timeframes may be a little off as i'm rusty on my Chrysler EEK and 6g72 knowledge but the transition between the 94-95 year was a significant one.

Use the Hall/Optical input jumpers.

My first reply was for a different engine; when Johnny cleared things up I drew up a possible set of wheel decoder settings to try.

Ah I see, however what about the sensor's 3 wires? It has a negative (which I assume goes to pin #2 on the MS?), a 8v supply from the ECM (do I connect this to pin 24 on the MS?), and a crank sensor signal (or do I connect this one to pin 24?). I think I could leave the 8v supply wire coming from the ECM as-is, and just splice into the crank sensor signal and wire it to pin 24 on the MS. Might I be on the right track here?

You'd split the signal wire and run it to both the stock ECU and to the MS pin 24. Leave the other connections as-is.

I really appreciate the help Matt. Hopefully you'll still be hanging around this message board when I buy this thing and get it all wired up!