It is possible to retrofit many old engines that didn't have an ECU with a modern fuel injection system.

My son drives a 1996 Buck Park Avenue which dates from the beginning of the ODB II era. We got it for about $4k but it has been through a few difficult repairs that took my son or auto techs a while to figure out. For instance the immobilizer system failed with the result that we couldn't start the car, it took a tech a lot of investigation to realize this, but once he did it wasn't hard to disable.

What would a defeat device look like for an electric car?

I suppose that hasn't been explored in the legal system currently. Most electric cars would be considered a zero emission vehicle. If you bolted a generator to an electric car that'd change its emissions. One could argue this defeats the original emissions target, but that sounds like a stretch.

Overall if the car has some sort of devices that limits, mitigates, or eliminates emissions then any modification to it can be considered a defeat device

> It is substantially easier to replace the entire computer system of most gasoline engines

Verses a carburetor? Have you worked on engines before?

I think that was "versus replacing a chip."

The ECU has fairly standardized interfaces, mostly CAN or just simple switching circuits on or off. You can just get a replacement ECU. These replacement ECUs generally don't do things like using the O2 sensor to adjust the fueling, so they can burn dirtier than the original ECU.

> mostly CAN

CAN is just the physical and framing layer. The data that goes over it is a whole different matter, and it's proprietary to every vendor, incompatible and generally undocumented.

For a lot of cars you can't even swap the exact same ECU between vehicles (due to bullshit like the VIN being written into it for no reason, and often no official way to change that other than "buy a new module" - so you have to hack around with reverse engineering & EEPROM programmers), let alone mix and match completely different parts.

> the VIN being written into it for no reason

There is good reason for this: theft protection. A long known crime model is the "chop shop" where they tow away a car, then cut it up for parts. Because the VIN is in the ECU a chop shop has less incentive to exist since there is less money in it.

It does of course make legitimate repairs harder, and probably there should be a process to write a new VIN in - but it should only be available to someone who can verify the ECU wasn't stolen (which isn't free).

EEPROM programmers and various other ways of rewriting this VIN (turnkey tools using undocumented diagnostic commands giving you unauthenticated read/write access to memory) means it's just one insignificant expense for the chop shop (as it's amortized over all their cars) vs a multi-thousand-dollar investment in money for a legitimate vehicle owner or part-time mechanic.

Only if it is done via EEPROM and not via something more complex. Though your point stands.

That's true, but it's usually pretty simple to reverse engineer, and that's been done for a lot of cars. CAN message are generally sent out at fixed time intervals, and correspond to some physical or control value, with a simple linear mapping between some physical unit and the value in the message. You collect some CAN data, change something like pressing the accelerator, see what changes, record results.

Just search for "aftermarket ECU", you'll find lots of them; generally for high-performance cars that gearheads want to soup up further, but the same basic principle applies to most ECUs.

I read it as agreeing with you by adding an interesting anecdote. Ie “yes, the old systems are easier to keep on the road. It would be possible to keep newer systems on the road with custom built parts (aftermarket ECU) but unfortunately that is illegal “

Carburetors are one of the most complex parts of a classic car and thus a bad example. If there are major carburetors problems it is probably simpler to replace it with fuel injection. (but only if a community of people work together - all the different maps and such in the ECU need to be created before you can make a useful fuel injection - this is long tedious work)