Intermittent crank-no start

[clueless1]

Hi there,

986S which has intermittently been not starting. This seems to happen only when it is warm. After I come back a few hours later the car starts again.

The tach moves slight when I turn the key to on position (regardless of whether it starts or not) — ie up to 0 rpm.

I bypassed the fuel pump relay with no change. The fuel pump sounds like it is coming on. No CEL.

When I crank the engine and the car DOES start I see a subsequent tach bounce initially (eg up to around 200ish and then it goes to 1000rpm on ignition). When I crank and does NOT start I see no tach bounce.

If I understand correctly, this is what a CPS fail looks like? Is there anything else I can do to check other than replacing the part?

[TrumpyAl]

The symptoms match a Crank angle sensor fault. The only way to test would be to use an oscilloscope of some description while the fault is evident.

I’d just go ahead and replace the sensor - even if it turns out to be something else, they are known to fail so a fresh one will benefit you down the line anyway.

[rexcramer]

I have not had this issue personally. But if I remember correctly from previous posts, if the crank position sensor is bad, the tach won't move while cranking.

[seningen]

The CPS is easy to change, can be done on jack stands -- its a bit of a blind access, but it's one bolt and
not too hard to get at once you find it.

just be sure to put a shop towel in the hole underneath the CPS, please don't ask why I know this to be important :-)

Mike

[elgyqc]

I have been having the same symptoms,
"intermittently ... not starting. This seems to happen only when it is warm. After I come back a few hours later the car starts again."

I changed the CPS (a used one from another engine) and so far so good after a couple of test drives.

Originally Posted by seningen

The CPS is easy to change, can be done on jack stands -- its a bit of a blind access, but it's one bolt and
not too hard to get at once you find it.

Mike

I created a thread with some helpful tips from my experience.
http://986forum.com/forums/performance-technical-chat/84177-changing-cps-crank-position-sensor-jackstands.html#post657480