EFI and Cutoff Switches

[Beagle]

I think the odds of killing it with a jump start are better than killing it by powering it down. I can't say how many cpu's I would have killed if that were the case. I thought that's what ROM, CMOS, and ePROMs are for... ?

[NewEnglandRaceFan]

3 wire alt, once powers cut from field + it's dead.. and can't hurt anything, no matter if you spun it with a drill.
it just free wheel.

[CTX-SLPR]

In the springs? Hmmm

http://www.firstandmaintowncenter.com/BookingRetrieve.aspx?ID=150420

Carshow/cruise I've been wanting to go for most of the time I've been here but the 2 weekends I had the time and working car to go there wasn't a cruise or show going on. Hope to finish the rewire and go to some again.

[Matt Cramer]

The real issue I've seen with battery cutoffs and EFI is if the cutoff is wired in such a way that some of the devices hooked to the EFI remain hot when shut down. That can have pretty messy results if the ECU stays partially powered up from voltage backfeeding into it, or an output that goes into an indeterminate state and leaves the injectors or spark outputs stuck on.

[Beagle]

The real issue I've seen with battery cutoffs and EFI is if the cutoff is wired in such a way that some of the devices hooked to the EFI remain hot when shut down. That can have pretty messy results if the ECU stays partially powered up from voltage backfeeding into it, or an output that goes into an indeterminate state and leaves the injectors or spark outputs stuck on.

That would make a lot more sense, but how would the cutoff be legal?

[Bob Holmes]

That would make a lot more sense, but how would the cutoff be legal?

Exactly.

[dieselgeek]

Guy screw it up ALL the time. I know that when one of those NHRA-style trunk mounted switches starts to go bad, it can do bad things to an ECU. Usually you can see a big voltage drop across the contacts before it becomes bad enough to do some kind of damage though.

[CDMBill]

I lived that experience which is how I found out that there are many different switches with different amperage ratings. The typical catalog listed Moroso product is rated at only 20 amps continuous. Overtime and much higher loads these brun at the contacts points and mucho noise ensues until it just won't run the car. I cut one open to see after I had those issues.

[Barry Donovan]

Honestly, I don't see the difference, but I'm far from an expert in the world of electrical and or EFI. In either case you're just disconnecting the battery. But what about one of the self resetting circuit breaker with an appropriate rating on the EFI main feed?

that has been around since the 80s.. it works.
probably call it a resetting relay, and not a circuit breaker.
they look like a turkey popper when they finally are really bad.

my subarus are 26 years old, I have 21 year olds as spares.
they simply bend the top outward when they are done.

seems oem would have all that basic smart stuff already.

[JCR Wiring]

If you wire the master cut off switch on the negative side of circuit the car wont keep running, and no other circuit can keep receiving voltage from the alternator, hope this helps any.

[CDMBill]

NHRA requires it to be on the positive side. I'm not sure what the rationale is, but that's the rule many of us live with. I run the alternator output to the terminal side of the cut off so the shut off doesn't create spike. And, I have a small #12 'clean' connected the positive terminal that supplies power to the relay for the MS3X only. That was the final step in getting all noise out of the grounds and the crank sensor signal on mine.