Kill switch

[blackjackT7]

Hey im building a new race car that is an 87 325IS. My question is about wiring my main kill switch. I was curious about the factory ECU and if by cutting all power to the car, will this negatively effect the ECU? If I hit that main kill will the computer have to go through its learning cycle every time? On my other car Toyota MK1.5 race car if I hit the main kill I know that the computer has to go through its cycle after every time. Will it be similar on this car? Also any recommendations on wiring up the kill. Last time I used the kill to interrupt the charging circuit and a separate wire controlled by the main kill to interrupt the coil. Not sure if this is the same rout i should take. Any recommendations would be greatly appreciated.

[Turbo Joe 87]

Not 100% sure, but it is extreme likely that killing the main power to the ECU will send it back to learn mode. That is the way the factories clear software issues. If I were to install a kill switch, I would break the coil circuit. This would shut the engine down the quickest.

Joe

[vpilarrt]

From what I've read the Spec E30 guys wire their ECUs so that the power to it is cut every time they turn the car off. You want the ECU to go back to the learn mode because otherwise it tends to lean out the mixture over time.

[blackjackT7]

Vpilarrt, do you mean they hard wire the ECU so that it always has constant power? In my series the kill must kill the main battery circuit and the ignition. . None the less its good to know that it will go back to learn mode. I will probably just wire it to kill all power and just make sure if we use the main Kill we know it is only for emergency's.

[ForcedFirebird]

We have installed many kill switches in e30's. I use a dual pole switch, the large lug goes to the battery cable, the small lug goes to the small wire that runs along the battery cable (DME relay power). Tried other ways and this works the best and is the easiest to wire. Never had any issues with ECU having to relearn. Some people like to use the alternator wire, but this will fry your alternator when you use the kill switch rather than ignition switch when shutting down the ca (or you will need a resistor to ground). Can't tell you how many times I have seen crapcan cars changing alternators because of improperly wired switches.

[vpilarrt]

Vpilarrt, do you mean they hard wire the ECU so that it always has constant power?

No, that's the way its wired normally. I mean connect that normally always hot wire to a hot on start and run circuit.

[TobyB]

Mine is wired as John's- and is just inside the passenger's window. The stock cabling
makes it there, and then you just extend both to get to the main lug
on the other side of the firewall. Out of the weather, easy for a corner worker to get to,
I can reach it if I loosen (but do not release) my harness. As in, when I'm upside- down
or sideways...

And yes, it then goes into 'learn' mode, but I've noticed no change in lap times while it's 'learning'.

I don't think it learns much about WOT...

t

[Boris3]

Think about why you want a kill switch in a race car. If you / corner worker are using it things have gone pretty bad and you want all power off to everything to stop bad from getting worse. The ECU having to relearn is the least of your worries.

Mine is set up the same way others have noted--main hoop passenger side. But I also run a repurposed choke cable from the hole in the plastic cutoff switch key along the harness bar and up next to the drivers seat with the pull knob attached to the ebrake arm. I can reach down with my right hand and kill the car even when fully strapped into the seat.

[blackjackT7]

Normally the kill switch is an emergency devise but a few times recently during fuel stops i have been getting hassled to use the main kill. Meaning just shutting the car off is not enough for some of the safety officials. Lots of the tracks are inconstant and some of the safety guys are volunteers that don't know better. I will wire it up just like you guys suggested and know that if they make me kill the car that way that the computer will be relearning. Shouldnt be a big deal.

[ForcedFirebird]

Normally the kill switch is an emergency devise but a few times recently during fuel stops i have been getting hassled to use the main kill. Meaning just shutting the car off is not enough for some of the safety officials. Lots of the tracks are inconstant and some of the safety guys are volunteers that don't know better. I will wire it up just like you guys suggested and know that if they make me kill the car that way that the computer will be relearning. Shouldnt be a big deal.

We actually had an issue at Daytona with the w211 and the main cut off. The drivers were cutting the main, rather than the ignition, it was going into relearn mode and would run like poop for about 30mins after. In my experience, it has been the drivers, not the officials doing it. According to most sanctions' fueling rules, the engine only has to be "off", not the entire electrical system.