4 replies to this topic

[Duncan]

First symptom:  The shut-off switch does not turn off the car.  It just continues to run.   This is a switch that's worked perfectly in the past, with no changes I can think of.  It's one of the 6 pole switches.  One set of contacts for the main battery cable.  A second set of contacts for the main IGN wire from the key.  The third set of contacts grounds the alternator through a resister when the switch is turned off.  I should also note that the engine was replaced this winter, but none of the wiring was changed.

 

Things I've discovered in my testing so far.

 

1.  Switch definitely functions correctly.  Verified all the contacts.

 

2.  Car starts and turns off normally using the key.

 

3.  If you try and shut off the car it does not turn off if you turn the key switch to off.  Everything stays on.  The alternator grounds correctly because the resister starts getting really hot.

 

4.  Pulled the ignition wires off the back of the switch.  Turned the key to ignition with the cut-off switch on.  The IGN wire gets positive from the 12v constant wire on the key, goes to the cut-off switch, and then continues on into the harness.  With the IGN wires disconnected from the cut-off switch and the key on, the IGN wire has power on both sides, which means it's getting 12volts from somewhere it's not supposed to.

 

 

5.  If you go in the engine compartment and turn the key to IGN, even with the IGN wires disconnected from the switch, several things in the engine compartment have power.

 

6.  Notably, the idle air control valve is making a high continuous wining noise.   Pulling the IGN fuse makes the noise stop immediately

 

I haven't done any further investigation, but I'm planning to look at some wiring diagrams tonight.  

 

Any thoughts on where to start?

 

thanks

Duncan

[Jaime Florence]

Duncan,

I had a very similar failure on my car...or at least it sounds similar.

Arrived at the track, drove off the trailer, everything fine. First session on track drove into the paddock and when I turned the key off the car kept running. So I reached over and shut off the master kill switch...and the car kept running. I stalled the motor and everything shut off and functioned normally,(key off would kill power and master switch off would kill power) until I started the engine again. Once engine was running ignition switch and master switch did nothing to kill power.

Turned out to be a wire in the fuse box had partially melted and was shorting out causing constant hot. Check the bottom of the fuse box and wiring in there maybe? Aaron solved it after Craig and I chased it for days and days...so he would have more info if it helps.

Oh, and I believe the master switch should be wired up in a way that should prevent this...but mine wasn't.

Come back to California!

Jaime

[Duncan]

So, I figured it out.    Figured some of you might find it interesting.

 

This winter I changed wide bands in the car.  I went from an LC-1 to the AIM system, which is CANBUS.  I wired the AIM system wideband power into the cigarette lighter, which is exactly where the old system got power from.  

 

What I didn't figure on, is that one of the CANBUS wires carries power between the datalogger and the modules, and by wiring it this way I was essentially connecting the ACC to the IGN circuit in the car.  

 

So when the cut-off switch was thrown, the power to the battery and the IGN wire were cut, however since the alternator is still turning, and the ACC wire is not cut, the ACC circuit powered everything on the IGN circuit through the AIM CANBUS system.  What's the most amazing thing, is that all the power for the IGN circuit went through a 20 gauge CANBUS wire, and did so without damaging any of the AIM components.

[Mark]

You might want to give AiM a call to verify the behavior. A good chance a diode is blown in the MXL. I had an MXL do exactly the same. The kill switch fix is a separate but necessary fix but the AiM system should not allow the CAN bus to provide power to non-CAN systems.

[Duncan]

You might want to give AiM a call to verify the behavior. A good chance a diode is blown in the MXL. I had an MXL do exactly the same. The kill switch fix is a separate but necessary fix but the AiM system should not allow the CAN bus to provide power to non-CAN systems.

Thanks Mark. I'll give AiM a call.

Duncan