GM HEI, stepper IAC, and wiring up the bypass. help?

flyguyeddy · Post by **flyguyeddy** » Mon Mar 06, 2006 12:14 pm

Ok, im running a GM DIS setup (similar to the HEI setup) and the stepper IAC with this engine. i need to know is there a way to operate the bypass with the megasquirt as they do it with the extra code, or do i have to rig up a relay? i would like to not have to make a relay setuyp, but if i have to i will. btw, im using a diy-autotune harness, so i can pretty much only use the wiring thats in the bundle. any assistance?

runing v3 board and 2.33 (i think)

Bernard Fife · Post by **Bernard Fife** » Wed Mar 08, 2006 6:05 am

is there a way to operate the bypass with the megasquirt as they do it with the extra code, or do i have to rig up a relay?

flyguyeddy,

There are two ways to do this besides a relay.

The first is to use 'trigger rise' for the 'Cranking trigger' setting. This essentially causes the module to behave the same as if the byapass were connected, but MegaSquirt-II is still involved.

The second way to do this is to use the spare port outputs. Since you have an IAC, you can use the FIdle output with a pull-up resistor/5V voltage source. (You connect the Vref to the HEI bypass line through a 1k Ohm resistor to limit current.) Then set the conditons so the Fidle LED is off when the rpm is <= to the cranking rpm (or the engine bit>2 and <5, etc., etc.). You could also reassign one of the LEDs for this function as these already have a pull up.

Lance.

DCU1976 · Post by **DCU1976** » Wed Mar 08, 2006 6:03 pm

use 'trigger rise' for the 'Cranking trigger' setting. This essentially causes the module to behave the same as if the byapass were connected, but MegaSquirt-II is still involved.

What are the Pro's and Con's with using this setting, and where exactly is it. Thanks!