2008-01-18

The (not so) good old days.

One of the thing that I hear when I discuss modern cars with people who used to love cars is "All of the electronics on a car make it impossible to work on!".

Umm... No. And I have the perfect example.

Fuel injection is a beautiful thing. Do not let anyone tell you otherwise, because of the alternative: Carburetors.

To explain it simply, a carburetor is essentially a (or several) very precisely machined tube(s) on top of your engine, that allows vacuum to suck fuel out of a precisely machined hole in the side of said tube(s), that has a reservoir of gasoline inside of it. On top of the tubes, are precisely machined flaps that effectively control the size of the tube. These flaps are connected to your accelerator pedal.

More simply put, it's a very precisely CONTROLLED FUEL LEAK. That doesn't adjust for anything, except the amount of air flowing by the jet.

Yeah... that was great when we didn't have options. Things have evolved a tiny bit since then.

We now have the ability to tell how far your lead foot is mashing that pedal. A throttle position sensor does this simply.

We now have the ability to measure how much air is rushing into the engine when you do mash that pedal. Mass airflow sensors do this for us.

We now have the ability to tell how dense that air is. A simple intake air temperature or manifold air pressure sensor does this for us.

We now have the ability to tell at what point each cylinder of the engine is in, via crank and cam sensors.

With this plethora of information, we can deliver fuel to the cylinder right as it starts down on its intake stroke. In precisely the correct amount for the amount of air that is being drawn into the cylinder. A good thing.

Why in the hell would we want to go back to a controlled leak? Really? I mean, it *really* sucked when driving across country, when you got into significantly different elevations than where you usually drove the vehicle, because one of two things happened:

  • It belched black smoke when driving up the hill, because the carburetor was set up for the soup that people at sea level call air and delivered too much fuel.

  • It ran hot and started knocking because the carburetor was set up to to have an auxiliary O2 tank on top to deliver enough air to actually burn fuel, thus not delivering enough fuel.

Either way, the performance suffered when the elevation changed more than a couple of thousand feet.

Closer to home, fuel efficiency went way up when we switched to fuel injection. Along with more precise measurement (due to knowing how much to deliver for the amount of air) and timing (due to knowing where every cylinder is at any given time), we can now also more precisely place the fuel at the valve, instead of letting it puddle inside of the intake. Ford is currently working on a direct injection system that puts the fuel directly into the combustion chamber, making the placement even more precise.

Tools are available for those who do wish to spin their own wrench. The computer is very good about giving very detailed troubleshooting information as well, at least on the later model vehicles.

There are places where technology has killed the art of the car. Fuel delivery and other engine management is not one of them.

1 comment:

Shawn said...

+1 for EFI... *way* easier to let the computer sort it out than to tune the carbourator