Alternator delete with regen braking modification for better MPG

[inuvik]

Correct. Its time to cut a wire.

More specifically, I did look up the wiring diagram in the service manual. I located the FR wire going to the ECU. The next step will be to cut it and solder in a switch.

Attachment 12461

I’m wondering if interrupting the circuit would cause a canbus error putting the Mirage in “Limp Mode”?

[Loren]

I’m wondering if interrupting the circuit would cause a canbus error putting the Mirage in “Limp Mode”?

I was wondering the same. It could very well trip a CEL or something. One way to find out.

[stevedmc]

I’m wondering if interrupting the circuit would cause a canbus error putting the Mirage in “Limp Mode”?

Not having clean power can cause all sorts of issues. I know this because I had problems with my drive by wire pedal earlier this year. I unplugged the wiring harness, put some dielectric greese on the terminals and plugged everything back together. So far so good. But that thing needs a clean signal to work otherwise the engine goes into limp mode (solid 1000 rpm).

I'm really curious if this would corrupt the firmware that runs the ECM. I repair printers for a living and I have a few complicated machines that get corrupt firmware regularly. The more complicated the machine, the greater the chances of the software getting corrupt and having to be reflashed.

If at all possible, I would highly recommend making a backup of the ECM firmware before making it a habit of running the system without an alternator. That way you can at least restore it if something gets corrupt.

[Loren]

I totally get what you're saying, Steve. But, cars by their very nature have to be designed to be VERY fault-tolerant. A car that lost its firmware because you left the lights on and ran the battery down, or whatever would be a HUGE liability for a car maker.

On a car, that's just not something you're likely to have to worry about.

And those sensitive sensors usually run on a 5v reference voltage that comes from the ECU. The ECU itself will usually run on something less than 10 volts (because your battery voltage on that VERY cold start in the middle of a Montana winter WILL dip that low), and supply that solid 5v reference no matter what.

In short, cars are designed better and more robust than printers. Because they have to be.

What CAN mess up an ECU is overvoltage on the inputs or shorting the outputs. You take that throttle pedal input that's expecting a maximum of 5v and throw 18v at it, and it might very well smoke something on that input circuit. Stuff like that. Overall, though... car computers are very robust. At least until they get old and the electrolytic caps start leaking and corroding the circuit boards.

[stevedmc]

I totally get what you're saying, Steve. But, cars by their very nature have to be designed to be VERY fault-tolerant. A car that lost its firmware because you left the lights on and ran the battery down, or whatever would be a HUGE liability for a car maker.

On a car, that's just not something you're likely to have to worry about.

And those sensitive sensors usually run on a 5v reference voltage that comes from the ECU. The ECU itself will usually run on something less than 10 volts (because your battery voltage on that VERY cold start in the middle of a Montana winter WILL dip that low), and supply that solid 5v reference no matter what.

In short, cars are designed better and more robust than printers. Because they have to be.

What CAN mess up an ECU is overvoltage on the inputs or shorting the outputs. You take that throttle pedal input that's expecting a maximum of 5v and throw 18v at it, and it might very well smoke something on that input circuit. Stuff like that. Overall, though... car computers are very robust. At least until they get old and the electrolytic caps start leaking and corroding the circuit boards.

Leaving the lights on doesn't really matter from a liability perspective. As soon as the car starts, providing you have enough power to turn the starter, the alternator provides the system with the proper 13.8 volts.

I spent about 15 years working in IT before my sligh career chabge as a printer tech. I've seen enough blue screens of death to scare me regarding computers in cars.

Drive by wire is something I really don't like. I've seen it fail on my car, but that's where cars are going so I just have to live with it.

My company requires me to drive a car that is no older than five years. If it wasnt for that silly rule, I'd be driving around in a 1981 toyota corolla station wagon.

I'm just saying be careful and make a backup of that firmware if you can. It's cheaper and easier to reflash an ECU than to replace one. It could very well get confused when you stop giving it the power it was designed to receive.

For what it's worth, I do acknowledge that I'm an idiot. I just learned that cars built in this century domt even have voltage regulators on their alternators. Lol

[inuvik]

My company requires me to drive a car that is no older than five years. If it wasnt for that silly rule, I'd be driving around in a 1981 toyota corolla station wagon.

That sentence made me think of “Breaking Bad” for some reason

[Fummins]

For what it's worth, I do acknowledge that I'm an idiot. I just learned that cars built in this century domt even have voltage regulators on their alternators. Lol

I'm an idiot too! I just learned that most cars have the power wire from the alternator going to the starter rather than directly to the battery. For some reason I can't think of one example where I've actually seen that off the top of my head.

[Daox]

Alright, lets get the alternator wiring modified!

Since I already found the wiring diagram, I can go straight for the ECU. For those who don't know, its right behind the driver's side wheel well. The connectors are covered up by a black plastic shroud.





Take out the two 10mm bolts and you will see the ECU and surprisingly less wires than I expected.





The C-225 is the farthest connector on the right, nice and easy to get to thankfully. The green wire on pin 21 is the one we are looking for. I've pulled it away from the rest.





Now for the moment of bravery, cut said green wire. I soldered on extension wires to mine so I could wire a switch to it and mount it where I can actually reach it.





On the other end, I soldered on a little toggle switch.





And, with that the mod was done.

Now for the testing. I fired it up and it surely appeared to be working. My scanguage said a wonderful 12.6V which is right where it should be. However, I did run into a bit of a snag. Once I revved up the engine a little, the voltage jumped up to 14.4V. Boo! So, it is self exciting somehow. This simply won't work. It started exciting (powering up) at probably a little over 2k rpm. Its not like I can just 'not go over 4,000 rpm' and make this work. So, its back to the drawing board for version 2 for this modification.

[Loren]

For what it's worth, I do acknowledge that I'm an idiot. I just learned that cars built in this century domt even have voltage regulators on their alternators. Lol

Apparently, I was wrong on that. The voltage regulator is still inside the alternator. But, the ECU does switch the alternator on and off. I'm guessing they keep it out of the ECU because there's some heat generated in the process of the voltage regulation process.

If you're really old, you remember when alternators were simple 2-wire devices, and the voltage regulator was a separate part. And so was the starter solenoid. And fuel pumps were mechanical, bolted to the side of the engine block. I don't miss any of that stuff.

[Loren]

I'm an idiot too! I just learned that most cars have the power wire from the alternator going to the starter rather than directly to the battery. For some reason I can't think of one example where I've actually seen that off the top of my head.

I guess they're not all that way, then. The cars that I've spent the most time with have been that way. One of those cars is the Miata, and with the battery in the trunk... it makes sense to not run two wires all the way back there. I'll admit that I've not wrenched on a lot of cars that are newer than 1997 or so, at least not in the vicinity of the alternator wiring. But, the starter is quite often pretty close to the alternator. And you've already got a giant wire running from the battery to the starter.

I just did a quick Google search. Alternator to starter (solenoid) to battery is not at all uncommon. Though I'm sure it's not the only way.