Does anyone out there know of any possible negative effects of connecting a relay & kill switch to the ECM? I realize this will erase the "memory" of the computer. I already have 1 kill switch connected to the neutral / gear selector wiring. This works great..turn the key and " nothing". I thought that a 2nd switch, hooked up to the ECM with a relay would make the IROC virtually "impossible" to start....without the computer, it could never be started or run. Since it erases the "memory", its a device that could be used only in the most extreme cases...dangerous area, parked long term, etc. Comments?Thanks.

 

DO NOT DO IT! The problem is this, some sensor's get power from key on voltage. With ECM power disconnected output drivers in the ECM could be damaged. All service manuals will state not to crank engine with ECM power disconnected. I realize that this would only happen if someone were trying to steal your car but what if you forgot to hit the switch. You don't mention engine, if you have fuel inj. why not insert a switch in the fuel pump power line.

 

The ECM has an ignition switched power source, correct? If so, why not add a hidden switch to that circuit?

 

Because when you apply 12 volts to the ECM, at the same time the sensors get thier power. I personally have never tried to do this but EVERY service manual says that you should never attempt to crank with 12 volts missing to ECM input. There is a lot of electronic theory involved, too much to get into here but the reasoning to me seems sound.

 

Thanks for the input. I would'nt want to risk damage to the ECM. Instead of the ECM kill switch idea, I went with kill switching the fuel pump ground wire (black wire to the pump in the hardshell at the fuel pump / gas tank ). Works great. When kill switch is on car stumbles / coughs as its cranking, then just cranks as though its out of fuel, and thats it!

 

pauls: First of all, the constant power wire for the ECM, as far as I know, is only there to keep memory. The car will run without power to that wire (just not long and not well). This lead runs directly to the battery via the fuse by the battery. This is the same fuse that you pull to relieve fuel pressure the book way. In case you're not following, you're cranking and running the car without power to the ECM or the fuel pump when you pull that fuse and you're instructed to do it that way in the book.

The switched power lead, which is fused in the fusebox, I think could cause damage like Danno said, if you crank the car without power to it. Even though admittedly it seems to me that if you ever blew that fuse and sat there cranking your car before you found out that that fuse had blown you'd be screwed every time the fuse blew..?

Either way, a second kill switch seems like it would be overkill if you hid the first switch well enough.