All cars with electronic ignition and fuel injection have a crank
sensor. A better name for this is crank position sensor. Usually it is a
pick-up that measures changes in a magnetic field as a "gear" moves past
the sensor. The teeth on the "gear" provide peaks and valleys that cause
a change in the magnetic field at the interface between the sensor and
the gear. Usually the "gear" that is used, is not an actual gear in the
sense that it mates with another gear to transfer power (although
sometimes it is). Usually the gear has one tooth that is positioned
differently or that is missing altogether to provide a "zero" reference.
A lot of GM cars (and others) have both crank and camshaft position
sensors. The crank position sensor provides the computer with
information on the location and rotational speed of the crank. The
camshaft position sensor allows the computer to know which cylinder is
on the compression stroke. This is important for engines that use
sequential fuel injection and/or that don't have distributors. GM
engines can deduce the compression stroke relationship if the camshaft
position sensor fails, but doing so increases the amount of cranking
time it takes to start an engine. So, a failed camshaft position sensor
usually first manifests itself by longer cranking times. A failed
crankshaft position sensor manifest itself by an engine that won't run.
Stark Raven wrote:
On 26 Nov 2003 15:48:27 -0800, email@example.com (davefr) wrote:
With a DMM you can check resistance of the sensor to see if it's shorted
or open. You can also check the output of the sensor when cranking by
looking for an AC (2 wire) or pulsed DC (3 wire) output during cranking.
This however tells you nothing about the quality of the signal. For
that you need a scope.
This may be an answer to my question. I was going to ask if checking
and/or replacing the cranksensor is an easy or difficult service
procedure. I'm taking my 95 Buick LeSabre,with 35,000 miles, to an
independent mechanic who charged $500 for replacing a key cylinder in
the steering column, which did not solve the problem. I'm sure he's
more than willing to try everything I suggest.
If I have an engine, 95 Buick LeSabre, 35,000 miles, that
intermittently takes anywhere from 6 to 20 cranks to start, but so far
has always started and run, I should NOT be looking at the crank
position sensor as a possible problem? This failure to run happens in
all weathers, on cold or warm engine and in sunshine and rain. It seems
Intermittently it may take anywhere from 6 to 20 attempts(cranks) to
start my LeSabre. The problem does not show up in an independent
mechanic's diagnostic, mostly because when in test, it starts. But a
couple of failures to start in testing seemed to point to failed
contacts in the key cylinder. Nothing else showed up in test. So the
key cylinder was replaced. $500.
The key cylinder was not the problem. The car continues to fail to
promptly start. Intermittently. Randomly.
Someone pointed out that the crank sensor may be the problem.
But another comment noted that with a defective crank sensor, the car
would simply NOT run.
My concern then was that if with a defective crank position sensor, a
motor will not run, the crank sensor is NOT my problem since mine runs
well after multiple attempts (cranks) to start it.
Yes the starter is turning the engine, as long as the key is engaged;
when I release the key the engine does not continue running. Thank God
I've got a strong battery; don't know how long that's going to last
when I have to crank the engine sometimes 20 times before it finally
catches and runs.
May be semantics, but I thought when the car is cranking it was the
starter motor turning the engine and the engine was not running until
the key was released. But my mechanic says the engine is running when
cranking; it just does not continue running when the key is released. I
don't know what that means, if anything.
On 12/26/03 8:34 AM, in article 261220030837223301% firstname.lastname@example.org, "Stark
Lots of Hondas in the '90s had this exact problem and it was the ignition
switch - the actual electrical switch that is screwed to the back of the key
cylinder. For $500 did your mechanic replace the switch, or the lock
My 92 Honda key cylinder costs about $300. It came with the ignition switch.
I bet they don't sell key cylinders alone.
Dear OP: If you thought when the car is cranking it was the starter motor
turning the engine and the engine was not running until the key was released
then you should do a jump start. Ignition modules tend to be voltage
sensitive. Try it: Turn on the high beams, rear defogger, maximum fan, radio
etc and see if you can start.
Thanks. The motor is definitely turning during the cranking. My
limited understanding of auto motors (maybe 20 years old) was that
during a start, it was the starter that turned the engine until it
caught and ran. My mechanic corrected me saying that during a start,
the engine is actually running, but that when the starter key was
release, it failed to continue running. 'Fraid the confusion is caused
by my limited understanding of automotive matters.
From reading around it seems your car should've warn you that the crank
sensor isn't sending a signal. If it sends wacky signals maybe it won't
display a code but it least it should seem like it wants to start. Maybe
most logic probe might show a signal from the sensor, maybe not. Anyways, you
might just check for fuel and spark. This narrows the field down.
Thanks. I think my problem is that without codes, there are a dozen
elements that could be checked and replaced. Unfortunately, a trial
and error approach to this problem could quickly cost more than the
value of the car.
You're right, it would cost money to keep troubleshooting. Most places charge
$80 per diagnose. I'd would recommend listening for the fuel pump. And then
check for spark, but then again, if it's a distriutorless ignition controlled
by an on board computer, the spark is too dangerous. If the fuel pump is
working and and the injectors are clicking then, the problem is likely
between the plugs and the computer. They make spark gap tester about $19,
don't know where.
Unfortunately I am unable to run these checks myself. I would hope that
my mechanic performed all of your recommended steps and still found
nothing amiss, either via the diagnostic or fuel pump, injectors and
spark gap check. And while my LeSabre sat on his lot for 10 days, it
started promptly when he chose to work on it.
for what its worth.... my dad had a 77 chrysler cordoba.... he had
problems with it starting as well, although his would either start or it
wouldnt... that was randam too... they replaced the on board computer and
the problem went away.... this probably wont help, but I d thought I'd chime
I've wondered about that too. But my mechanics don't seem too
interested. Of course I'm remembering when replacing onboard computers
costs around $90. I suspect replacing onboard computers these days
cost considerably more.
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