Downside of EFI/ECU/Electronic ignition

So it's the ignitions fault that the battery terminal was/is dirty and most likely causing the battery to go dead. Hmmm! And you want another "special" battery in the car so this no start won't happen?!?! Does this "special" battery clean it's own terminals, cause if not, your gona need another/more batteries!!! LOL

It's called an emergency jump starter. It's a supplementary

12 V sealed lead acid battery that connects to the main battery via jumper cable style clamps. I used one four times in the last month. I used it first to help out said friend after the lights were left on. Then going with said friend on a couple of road trips, I figured I should take it along with us.

It had enough to start the alarm and all the electrical devices. I personally left on the lights, and it bailed me out three times. Really - what cars these days don't have a warning bell or automatic shutoff (on removal of the key) if you leave the light switch on? ;-)

Turns out the problem was the battery- the post had mostly separated from the plate buss. In old days I would have probably still been able to push start it and eliminate borrowing a tow rope to tow it to the shop.

No, Don's idea is acually pretty good. Basically it would provide a power source *just* for the computer to use during cranking/low voltage situations. It'll never happen because it would add a horrendous $10 or so to each vehicle, and would have to be periodically replaced (every 5 years or so). But it's a pretty damn good idea, truth be told. It would enable push-starting with a dead main battery as Don described, and I've even had cases where a cell went dead and the battery could crank the engine over reasonably fast, but the computer would reset durning the voltage drop on every compression stroke and so the engine wouldn't fire. The "computer backup battery" would enable a start under that condition as well.

So how would you power the fuel pump, which is needed to start the car, and is no insignificant load?

I don't know about Don's car, but the Ford EEC-IV injection I have experience with works fine down to 8 volts or so. The ECU runs on 5V, and is powered through a plain 7805 style regulator. It will work, in LOS (Limited Operation Strategy), even if the processor is completely dead.

The fuel pump will probably be able to generate enough pressure even on

5-6 volts. I was surprised to discover that my wife's car would *idle* with a completely dead fuel pump, although you certainly couldn't drive it. The normal idling fuel pressure is 40 psi, so I figured for sure that pulling the fuel pump relay would shut down the engine after a few seconds, but I soon found that it will just idle away indefinitely, even after the fuel pressure drops to zero. I guess manifold vacuum pulls *just* enough fuel into the injectors to allow it to run, although the minute you touch the throttle it will stumble and die.

The problem with starting a car with a weak battery, in my observation, isn't the average low voltage but the very deep voltage dips that happen when the starter turns the engine through every compression stroke, which tend to reset the computer. In my wife's car when this happened, you could see the instrument cluster lights go back to "full test" mode every stroke. Since engine controllers need between a half turn to two full turns of the crank to line up the ignition and fuel timing, it just never gets there even though the engine is still turning over plenty fast enough to start if it were a carbureted engine.