FIRE UP YOUR IGNITION
by Jim Lunson
One
of the more difficult electrical items to understand on our MGs is the
starting and ignition system. This system does two things: first,
it modifies the entire electrical system during the starting mode to put
every ounce of battery juice available onto the starter motor, and
secondly, it provides the electrical current to the spark plugs which
need to fire in order to ignite the gasoline in the cylinders.
Everything else electrical in the car is secondary to providing these
functions: starting and running the engine. These other systems
accomplish many different functions, and depending on the age of the
cars, they vary greatly in their complexity. But the starting and
ignition systems function about the same in all MGs, regardless of age.
The electrical
function of starting the engine is accomplished by use of a relay.
A relay is a type of switch that, when low amperage current is supplied
to one side, it opens or closes a separate secondary switch that
contains a much higher electrical current. In the starting system,
in order to provide the starter motor with as much current as possible,
this secondary circuit uses very heavy wire and thus requires a very
heavy switch to connect it. It is so heavy that the item is called
a solenoid instead of a relay, but functions the same. When a low
amperage current (#16 or #18 gauge wire) flows from the ignition switch
(key on or button) on the dashboard, it closes this heavy duty solenoid
switch and sends a large current directly from the battery via the big
fat wire (#4 gauge) to the starter. This heavy wire and switch get
all the power possible from the battery directly to the starter to spin
the engine fast enough to start. The starter motor has to be very
powerful to spin the engine fast enough to start and it draws more
current than anything else in the car. That is why it requires
such a heavy wire and this heavy wire requires the big solenoid switch
to make the contact.
The second thing this solenoid does is disconnect
almost all other electrical current in the car. This is why the
radio comes on when the ignition switch is in the run mode, but cuts off
when the start mode is activated. Same for the blower, wipers, and
just about everything else electrical in the car except the headlights.
The idea, again, is to get as much power to the starter as possible,
this time by cutting out everything else electrical that might suck
current away from this effort. And its the reason you should not
try to start the car with the lights on.
Have you ever turned the key or pushed the start
button to start the engine and instead of the familiar whirr of the
engine cranking, all you hear is a rapid clicking sound? This
sound is the solenoid trying to engage the heavy duty switch to connect
the starter, but due to a weak battery, gets just enough current to
activate the solenoid but not enough to throw the heavy switch inside.
Just enough electrical current to keep trying over and over: hence the
clicking, but no contact and no starting. There is usually enough
power still in the battery to run the radio, lights and most other
electrical items, so the battery seems to be fine, but that starter
motor requires so much juice that the switch just cant close to get the
power through.
One possible solution when you hear this clicking
sound short of getting a new battery is to check the connections on the
battery and solenoid. Because this starting mode requires so much
current, the connections are very large, providing a wide connection
surface for lots of juice to flow through. If any of these
connections gets loose or corroded, electrical current to run the car
will still flow, but not when every ounce is required for that starter.
So, when the clicking sound is heard, first check and clean these
connections. This includes connections on the battery, the battery
to frame ground, connection to the solenoid, to the starter and the
engine block to frame. If that doesnt do it, then get a jump from
an outside source and see about a new battery. I once had a
battery that worked fine, until Ann and I stopped at an overlook in
Shenandoah Park. A cloud rolled in on us while we were there (very
pretty) and the sudden moisture from it was enough to weaken the
connections. When ready to leave, the solenoid started clicking in
stead of starting. Fortunately, we were able to roll downhill far
and fast enough to jump start the car. Once, down the mountain and
out of the cloud, everything was fine again. The moisture brought
in by that cloud was just enough to weaken those big connections enough
so there was not enough current. You'd better believe I cleaned
and tightened those connections first chance I had.
I also recently saw an MG where the starter motor
mysteriously burned out. In checking we found a faulty ground from the
engine block to the frame. Adequate electric current got to the
starter just fine, but it was unable to flow back to the ground and
instead melted the coils in the starter. So be sure to check that
connection also if there is trouble. It is usually way out of the
way under the car by the transmission mounts, but is also a heavy wire
and a crucial link in getting the starter to crank.
One item to note on car batteries these days too: new
modern auto battery construction utilizes alkaline chemicals in lieu of
the old acid types. This change permitted the sealed tops
(maintenance free!) which eliminated the little removable screw caps
that needing checking and occasional filling with distilled water
(remember them?). In addition deleting this maintenance step, the
newer construction lasts much longer. Warranties of 7, 8 or even
10 years are now not uncommon, whereas before 3 years was about the
maximum you could get. So there has been great progress in this
area of automotive science; however, one downside to this change is that
the newer batteries tend to fail all at once rather than gradually
losing starting power. You can start the car with almost full
battery power, drive to the store, and find the battery completely dead
when you get ready to return home. No warning, no weak starting,
and no reviving - just dead, and often so dead it wont even provide the
clicking sound described above.
So it pays more than ever to keep an eye on the age of
your battery, not waiting for it to show signs of weakening before
replacing it. And, if you wish to do a little easy preventative
maintenance on your battery, check your paperwork to see how long you
have had it and how long it is rated to last. Chances are if it is
past the rated lifetime, you may be in for a surprise one time when you
go to start your engine. It's easy to check and a replacement now
may save a lot of headache.
I'll go over the ignition system in the next issue as
to how the electrical juice gets from the battery to the spark plugs to
get the engine firing. It's another system that is vital to the
running of our cars and one that is often not understood. It
involves coils, distributors, points and other exciting parts of our
cars. How they all work together and what can go wrong.