>From: "Josh A. Kablotsky" <joshua.kablotsky@analog.com>
>
>When I tried to start the MG, I experienced a problem that began
>appearing in October. Now and then, the car wouldn't start. It's as
>if the battery were dead -- I put in a new battery after the engine
>rebuld last winter. I heard the solenoid click, the engine turn for
>a fraction of a second, the lights dim, and then nothing.
>
>Sometimes I'd hook up my battery charger. The charger is rated for
>50Amps cranking power. If I tried starting it with the charger
>connected, the charger would click indicating I was pulling all 50
>amps it would give, but the engine wouldn't turn.
>
>What is going on?
>Do I have a short in the starter?
> -> Then why would the jump start do it?
>Is my starter solenoid misbehaving?
> -> If the contacts were dirty, wouldn't it act as an open, not a
short?
>Is my almost new battery the problem?
> -> Why did it take 6 months to start acting up?
>Is it the charging system?
> -> Having it not start doesn't seem connected to driving for any
time.
>A starter ground problem?
> -> Again, wouldn't it act as an open?
First off, 50 amps is not enough to start a car without help from the
battery -- especially on cold mornings. If the charger were
attempting to do the job alone, a click is about all I would expect to
get. Therefore, your apparent conclusion that there is a short rather
than an open may not be valid.
The first thing to check is whether the problem is in battery or
wiring. Get a multimeter, preferably digital, and hold the probes
directly on the battery terminals (NOT on the connectors clamped onto
them) while you try to start the car. If the car starts OK, voltage
should drop from 12V down to 8 or so while turning over. If solenoid
clicks and lights dim, and the voltage drops to 5 or less, you either
have a battery that is either discharged or defective, or a dead short
to ground in the system. If solenoid clicks and lights dim, and the
battery voltage stays near 12, you have a bad connection somewhere.
If battery voltage drops to around 5:
It is easy enough to have the battery checked. AutoZone, and perhaps
many other places, will test the battery for free. If the battery is
OK, perhaps it is not being charged properly; most alternator shops
will test your charging system for free, if you can get the car
there. You can also get an indication with your multimeter connected
accross the battery with the engine held a 1500-2000 RPM or so:
voltage should be above 13. If 12 or less, charging system is not
working.
I seriously doubt if your problem is a short, but if it is, hold the
starter on, with the lights dimming, for about 10 seconds. Then, feel
all the wires you can between the battery and the starter. All wires
before the short will be warm, all after will be cool. If they are
warm all the way to the starter, either the starter is shorted or the
engine is siezed.
If battery voltage stays around 12:
Connect the multimeter accross the starter (between the terminal to
the motor itself and the housing) while starting; if you get nearly 12
volts while the car doesn't turn over, your starter needs work.
If the voltage at the starter is significantly less than at the
battery, you can go over every connection with the multimeter while
trying to start the car. The voltage accross any individual
connection should read nearly 0 volts while starting; for example, the
voltage between the battery post itself and the connector clamped to
it should read 0 when starting. When you find a connection that reads
voltage, you have found the problem; correct the connection and resume
your life. Be sure to check the ground side of the circuit along with
the hot side.
One of the connections to check in this manner is the solenoid. When
engaged, there should be nearly 0 volts accross it as well.
--
--- Kirbert
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| Kirby Palm, P.E. |
| palmk@freenet.tlh.fl.us |
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|