|
If it hadn't been for the invention of the self starter, automotive history
would've been profoundly different. Hand cranking would've limited the use of
big, high-compression engines to body builders and gorillas, and even small,
wimpy powerplants would require more physical effort than could be mustered by
the frail, the elderly, and (dare I say it in this age of political correctness?)
most women.
But engineering, like nature, abhors a vacuum. The need was clearly
recognized by the right person in 1911 -- Henry Leland, founder of Cadillac, was
badly injured when he tried to restart his car on a bridge. So, he commissioned
Charles "Boss" Kettering, head of Dayton Electrical Co. (Delco to you),
to come up with a dependable cranking system that didn't involve human sinews.
The next year, all Cadillacs had electric starting as standard equipment.
So we exchanged sprained wrists and ruined backs for another set of troubles.
Starting system malfunctions range from a total lack of rotation to noisy
engagement and slow cranking, none of which can be tolerated for long. The
actual replacement of the parts involved doesn't require any special skill, but
finding out the exact cause of the problem sure does -- without it, there's a
good chance that perfectly healthy components will be replaced unnecessarily.
This section is intended to help you insure against embarrassing and expensive
mistakes.
Read my sound
The first step in the investigation of a starting complaint is to listen
while you twist the key. If there's silence, turn on the headlights. If they're
dim or don't go on at all, the battery and/or the connections are probably at
fault. The same is true in cases where the lights get noticeably dimmer when the
ignition switch is turned to the Start position. In a complete no-crank
situation, if they continue to shine brightly when you turn the key, there's an
open in the circuit somewhere.
If the solenoid clicks once, but the starter doesn't run, the battery and its
cables should again be suspect, but a jammed engagement mechanism or a seized
engine could be the problem. A chattering solenoid is either not getting
sufficient current, or has a faulty hold-in winding.
Slow cranking may be the result of high electrical resistance, a low battery,
a bad starter motor, or excessive internal engine friction. If lethargy is
accompanied by unevenness, incorrect valve timing due to a broken or jumped camshaft
drive belt, chain, sprocket, or gear is a distinct, if unpleasant, possibility.
If the starter motor spins freely, but doesn't turn the engine, or you hear a
grating, grinding, gnashing noise that stands your hair on end, your on-car
troubleshooting efforts can stop here. You know immediately that the starter has
to come out so you can examine the pinion and flywheel
teeth and the engagement mechanism.
If you haven't isolated the offending component yet, it's time to check the
battery as explained in the preceding section.
Draw conclusions
Nothing will give you more useful info on the condition of that husky
electric motor than a starter draw test. The simplest way to do this is to kill
the spark, then use an inductive ammeter around the cable. A more comprehensive
procedure involves a load tester, to wit:
- Run the engine until it's thoroughly warmed up, disable the ignition, and
hook up your tester (load off). If you should happen to be using separate
meters, put the carbon pile in series between the ammeter's negative lead
and the battery.
- Crank the engine for 10 seconds and note the battery voltage reading just
before you stop.
- Turn the variable resistor/carbon pile knob until you get the same
voltmeter reading obtained in step 2.
- At this point, the ammeter will indicate the starter's current draw.
If more than the specified number of amperes is being consumed, the possible
culprits are a bad starter motor, a cable that's shorting to ground, or high
internal engine drag (if the complaint is slow cranking when hot, the lube may
be draining off the cylinder walls, and, if flooding is involved, the gas may be
washing that precious oil film away).
On the other hand, if the draw is below specifications and the engine cranks
slowly, you've found high resistance in the cables (watch out for cheapo
replacements that are more insulation than copper, and a cable repair that
involves one of those resistance- and corrosion-prone emergency clamps), engine
ground, solenoid contacts, or the starter motor itself (slow hot cranking with
low draw may due to a missing starter/solenoid heat shield). A related
indication is a battery voltage reading that doesn't drop a normal amount while
the starter's engaged (in other words, it stays above 11).
Drop
While cranking, voltage at the starter motor's hot terminal should be the
same as that at the battery. If not, you're losing something between the juice
source and the motor. For example, say the battery dips to 11 volts while the
starter's running, but you only see seven volts at the motor stud. Four volts
aren't making it to their appointed destination, whereas the max allowable loss
is half a volt.
Which brings us to voltage drop testing, something that's often misunderstood.
What you're looking for is an unintended load in the form of resistance. It'll
show up on an accurate, low-reading voltmeter because it requires juice. The
meter will detect an electrical potential across it (only while the starter is
cranking, of course). Why not use an ohmmeter to measure resistance directly? It
won't tell you anything useful because it can't assess the connection or cable
during heavy amperage flow.
To check the drop of the entire starter motor feed circuit, connect your
meter's leads to the battery plus post and the positive terminal of the motor
itself. Anything more than .5 means you've found unacceptable resistance.
Now, cut it up into segments. Put the voltmeter between the battery's
positive post and the solenoid's battery terminal, the negative post and the
starter motor housing, and the solenoid's battery and motor terminals. Any
reading of over 0.3 volts indicates excessive resistance somewhere in the
circuit between the two points.
Other angles
In cases where you haven't found anything amiss yet, but the solenoid doesn't
click, check the voltage drop between the solenoid's battery and switch
terminals. If it's over 3.5, the starter control circuit has a problem. Use a
jumper wire of adequate capacity to bypass the neutral or clutch safety switch,
ignition switch, or related wiring. If the problem disappears when one component
is thus taken out of the circuit, you've fingered the culprit.
Measuring the voltage available at various points in the system is another
important diagnostic procedure. For instance, at normal temperatures a typical
solenoid will operate when it receives eight volts at its switch terminal, or
somewhat more if it's very hot. If you find more voltage than that, but hear no
click, the solenoid's defunct.
It shouldn't take more than eight volts at the motor's armature terminal to
make the starter run. If more than that amount of voltage is present, but the
motor won't spin, the most likely causes are bad brushes or windings. Or, maybe
the engagement mechanism is jammed. Either way, the starter must be removed for
further examination. Unfortunately, there's another possibility: a seized engine.
Try to rotate the crankshaft
using a socket and bar at the pulley or damper bolt. If it won't budge, the car
is suffering from a much more serious ailment than a problem in the starting
system. |
