So I'm in the process of building an engine for my '88 IROC-Z which I'm going to swap to EFI from the current TBI. I'm going to be using a MicroSquirt and I'm charting out all the connections I'll need to make when swapping my ECM out for the MicroSquirt.

Most of the connections can be directly swapped over from the current ECM wires, but I ran into a problem when researching the MicroSquirt wiring diagram.

The diagram MicroSquirt presents as a summary shows a 'Main Relay' which connects to the ignition switch. This main relay powers the MicroSquirt and is required for certain connections. For example the MicroSquirt requires the use of the 'Main Relay' for the HEI Distributor connection stated on their website:

"A wire can be run from the 5 Vref to the HEI pin B through a relay that is switch from a source that is hot in RUN but not CRANK"

Can anyone tell me where I can find a source that is hot in RUN but not in CRANK as stated above?

Here's the wiring diagram MicroSquirt provides:

 

http://www.megamanual.com/ms2/GM_7pinHEI.htm
Have you looked at the hei page ?
Wouldn’t the hot in run be the ign coil +

 

The ignition coil is directly connected to the ignition switch, but it is also hot in the crank position.






The

 

Alt wire ?
Not sure what the sense wire produces on a cs alternator.

 

I'm thinking the TAN/WHT or BRN wire from the alternator pin F would be a good option, however...



It looks like that wire is connected to the Orange Accessory wire from the Ignition switch, which is hot in the ON position for sure, because you can turn the blower on when the key is switched to ON.

I believe the Vref wire from the MicroSquirt has to be connected to a relay that is only switched when in the RUN state, but I may be mistaken. The Vref wire is used as a reference for the MicroSquirt to set the distributor's timing. I don't know if it matters that the relay is on when the key is in the ON position because the motor isn't even running. The only reason it can't be hot in CRANK is because you don't want the MicroSquirt to be trying to control timing on startup, only when running.

 

Perhaps the wiring of the MicroSquirt is different than the MegaSquirt I, II and III that I have ran but I have always used the stock ecm's power wire to power the MegaSquirt. I've never had an issue.

 

The wiring between the MicroSquirt and the MegaSquirt are slightly different, (the IAC for example) but for the most part they are the same. I'll have to do some probing around to see which ECM connections are hot in RUN but not in CRANK so I can use that as the switch for the relay I need.

Sent from the mobile client - Forum Talker

 

"Can anyone tell me where I can find a source that is hot in RUN but not in CRANK as stated above?"

Try the power wire to your radio.

 

^^^ This is the answer.

Wire it in just like the stock ECU.

Curiously, what happened to the stock harness?

Here is some documentation I wrote a few years ago:

http://members.cisdi.com/~anesthes/projects/megasquirt/



-- Joe