Downside of EFI/ECU/Electronic ignition

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Don Stauffer in Minnesota - 04 Sep 2007 15:23 GMT

Car had dead battery and badly corroded battery cable. We tried to
push start it but the failure to start was expected (battery was at
ten volts).

That was one good thing about a Kettering ignition. With a stick
shift car, especially a light one like my Neon, you could easily start
them by a little push. I even had a Datsun that was light enough that
I could get it rolling myself, jump in and put it in gear and start
it. Even on a 12 volt system the coil would give enough spark at even
7 or 8 volts. Not any more with computerized/electronic stuff. You
need almost full battery voltage to get the engine electronics
working :-(

I think they ought to have a special battery- say a NiCAD, that
charges off the main battery, but with a diode, so it cannot see
starter load. And that auxilliary battery should only feed the engine
control computer/ignition/efi.

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dahpater - 05 Sep 2007 03:13 GMT

On Sep 4, 10:23 am, Don Stauffer in Minnesota <stauf...@usfamily.net>
wrote:

> Car had dead battery and badly corroded battery cable. We tried to
> push start it but the failure to start was expected (battery was at
[quoted text clipped - 13 lines]
> starter load. And that auxilliary battery should only feed the engine
> control computer/ignition/efi.

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

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y_p_w - 05 Sep 2007 07:57 GMT

> On Sep 4, 10:23 am, Don Stauffer in Minnesota <stauf...@usfamily.net>
> wrote:
[quoted text clipped - 22 lines]
> 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? ;-)

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Steve - 05 Sep 2007 17:46 GMT

>>> I think they ought to have a special battery- say a NiCAD, that
>>> charges off the main battery, but with a diode, so it cannot see
[quoted text clipped - 10 lines]
> 12 V sealed lead acid battery that connects to the main
> battery via jumper cable style clamps.

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.

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Thomas Tornblom - 05 Sep 2007 19:18 GMT

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.

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Steve - 05 Sep 2007 19:27 GMT

> So how would you power the fuel pump, which is needed to start the
> car, and is no insignificant load?
[quoted text clipped - 4 lines]
> 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.

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Don Stauffer in Minnesota - 05 Sep 2007 15:16 GMT

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.

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