crank sensor?

It's been 30 degrees below zero lately and my car acted like the
battery was not even there and there was no sound at all, not even a
click. I got someone to jump it , then test drove it about 10 minutes
and the electrical seemed almost normal (heater fan, lights, but not
the automatic seatbelt). Then I turned off the key and tried to start
it again and there was once again dead silence, as if I had never
turned the key. I've searched the internet and it seems it may be the
crank sensor. Does this sound right? It's a 94 SL2. Could it be
that I didn't let it charge long enough before stopping the engine?
Can anyone help me diagnose this? Thanks.
Suzanne

 

It is most certainly something other (SLIGHT maybe in addition to) the crank
sensor.

The crank sensor sends pulses to the computer WHEN THE ENGINE IS TURNING to
tell it where the crankshaft is. If the crank sensor is not operating, the
starter will turn the engine, but the engine will not start (no fuel or
ignition because the computer doesn't think it's turning).

If NOTHING operates (no lights, no radio, no nothing) then suspect the
battery and the connections to the battery. If things light up, but the
starter simply refuses to turn, then suspect either the starter, the
ignition switch, or the park/neutral switch in the transmission.

If the battery has failed, also check the alternator really carefully (or
just replace it). Bad batteries kill alternators, and bad alternators kill
batteries.

 

The crank sensor would not cause a no-cranking condition. I'd say most
likely your battery is weak..

 

Sounds like your battery is bad, or possibly the terminal posts/connectors
are no longer making a connection and need to be cleaned or replaced. I'd
put my money on the battery. I've seen them fail internally with an "open"
between the battery cells or the posts. This sounds like what you have here
to me, although you would need to measure the voltage across the posts with
a volt meter.

If this is the case, when you are driving after the jump start, then your
nominal 13.8V is likely much higher, running at the regulator's battery
charging voltage, most times upwards of 16V. This can have bad side effects
on the other electronics (computers, radio, lights, etc.) if not corrected
quickly.

Good luck.

Bob

 

The crank sensor would not cause a no-cranking condition. I'd say most

Definitly sounds like a dead battery to me.....

 

Are you saying that everytime you have your car jumped you are quite
possibly damaging components? Also, is it true that it's not good for
a car to jump other cars? Thanks
Suzanne

 

Suzanne,

When you jump start a car that has a "dead" (actually discharged/less than
fully charged) battery, the maximum voltage at the jumper cables is limited
by the two batteries which are effectively in a parallel circuit. As such,
the theoretical voltage across the jumper cables is 13.8V (6 lead/acid cells
in series) so assuming it is done correctly, no damage should occur. That
said, the actual voltage can be a bit more or less depending on the
condition of the batteries, the amount of current flowing through the
cables, and the gauge (resistance) of the cables, but this is really
insignificant for this discussion.

The damage I was referring to assumed the "dead battery" had an internal
"open circuit" and this would occur once the car had been started and the
jumper cables were removed. At this point the good vehicle's battery would
be removed from the circuit and the alternator and voltage regulator would
put out maximum voltage without the bad battery being there to hold the
voltage to the 13.8V nominal. Most sensitive electronics have some form of
protection built in or are designed to temporarily handle voltage spikes
from the vehicles electrical system, but I was just stating that if these
failed there could be permanent damage. Even without a complete protection
circuit failure, you also risk shortening the life of the components by
running them at this elevated voltage.

Bob

 

Is the alternator on these cars internally regulated or is the regulator
part of one of the computer functions? The only connection I would speculate
on is for an externally regulated alternator where the crank signal is used
to delay application of the alternator field current until the engine is
started and up to speed.

I would expect though that if the crank sensor was defective or even
intermittant, that it would go into limp home mode and throw a service
light.

educated guesses only,
Oppie

 

I do not believe the engine could run (even in a limp along mode) without a
crank sensor since it provides the proper piston timing/positioning signal
to the engine computer. That said, the computer might be able to infer the
valve positioning (provided by the cam sensor) from the crankshaft/piston
position since they are connected by a timing chain, so it may be true that
it could possibly "limp" along without the cam sensor, but I seriously doubt
that it could do so without the crank sensor signal.

This is my opinion based on experience with non-Saturn vehicles. I will
leave this theory to someone who has a factory service manual and can state
authoritatively for certain what actually happens if the crank sensor is
defective.

Bob

 

It wouldn't run without a crank sensor. There is no real cam sensor per se. The
computer can deduct which cylinder is firing by monitoring the spark plug
wires(thats why they need to be crossed) but in order for it to be firing in
the first place the crank sensor needs to be functional.

Jamie

 

I do not believe the engine could run (even in a limp along mode) without a

Where I wrote something like "which cylinder is firing" replace that with
"which cylinder is firing under compression" since with the waste spark system
it fires at every TDC instead of just compression stroke.