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Comment by chrissnell | Hacker News Reader

There's a cleaner way. You can use a battery terminal disconnect directly on the battery:

https://www.amazon.com/dp/B001N729FS/ref=cm_sw_r_cp_api_p1xP...

Personally, I drive an old diesel truck and it's as simple as disconnecting the fuel cut-off solenoid wire from the solenoid. Old diesels like mine are terrifically simple and really only have two wires: the starter positive lead and the fuel cut-off lead. The cut-off lead opens a solenoid that lets fuel flow to the motor. Remove power and it shuts the flow and stops the engine. The easiest way stop a completely mechanically injected diesel.

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Please don't do this if your car has oxygen sensors, a catalytic converter or fuel injectors (basically all cars 1980+)

Why? Besides polluting more you're going to reset the car's ECU and it takes a few drive cycles in different conditions to properly tune the engine.

There are so many things that can affect the tuning, engine wear, fuel quality even the barometric pressure. If the car can't learn that (because it's designed to reset on power loss) you will probably be running a rich A/F mixture that can foul your O2 sensors and 3-way cat.

Install an alarm or get a car immobilizer. There is a RFID immobilizer on ebay for less than 10 bucks..

Yeah, I'm in favor of a fuel pump disable switch instead. Any passenger car with fuel injection will have an electric or electronic fuel pump, and splicing in a switch is fairly simple. Hide the switch where it's out of sight but easy to access by the owner and Bob's your uncle.

That won't work for a whole pile of cars, especially German ones. They will lose the throttlebody sync and you won't be able to get it out of 'limp' mode without some ODBII reset and re-sync magic.

Essentially the ECU will no longer know what position the throttlebody servo is in and to avoid engine damage it won't allow more than 1500 RPM or so.

Huh. Good to know, thanks.

I installed a battery disconnect on my 2006 Jetta when my mechanic couldn't figure out why the battery was draining overnight. There was a short somewhere.

I found someone to clean the sunroof drains (I had cleaned all the drains I could figure out) and the electrical problem went away. Bonus, the notorious Jetta foggy windows on start problem went away too.

Now, I'm hesitant to remove the disconnect switch because I don't know the root cause. But with your pro tip, I guess I need to resolve this one.

I learned this the hard way, I ended up driving 55 km to the nearest dealership in 'limp' mode trying to maintain enough speed not to annoy traffic around me. It worked but that was one of the most annoying road trips I ever made.

The weird thing is it does not happen every time you disconnect the battery, but when it does disconnecting it and reconnecting it does not clear the problem. Highly annoying. But a good way to learn new German words ("Drosselklappe...").

That seems like quite a hassle to pop the hood every time you're ready to drive the car, then pop it again when you're done. It also would prevent electronic locks from working.

Much simpler to install, for sure. But having a hidden toggle switch somewhere is a lot simpler for every day operation IMO.

And you'd have to reset your clock, and preset stations. Also the fuel trims the ECU is using would be wiped out.

That product is pretty cool though, I didn't know they existed. Makes sense for an RV or something you rarely use.

It is also not recommended for Euro cars like bmws. They are finicky.

Car batteries can explode from sparks... I wouldn't want to be disconnecting the battery every day increasing those chances.

https://www.youtube.com/watch?v=d_TnsHu2u4c

That won't work, my car had those on both terminals and the battery was flat. They brought their own battery and rigged it all back up. It might stop an opportunist doing his first theft though.

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