Question about cam sensors...

Bacondoggy

Registered User
I have heard opposite things about them and its one thing I never replaced. I have heard this (and things along the same line):

the cam sensor only really is used to start the car, once the car is started it doesn't effect the car. So if you car fires up its fine. If it won't idle did you check your IAC = Idle Air Control valve? Maybe its faulty or sticking open or closed. Try spraying it out with brake cleaner. Also what IAC are you using? If you car is a 94-95 then you can use the SC IAC or Mustang IAC, but if your caris a 96-98 then you MUST use the Mustang IAC.

and this:

The reason why you disconnect the cam sensor to look for a change, even though you have odd running conditions is that if the sensor is failing in an odd way, it can send incorrect information to the eec, or intermittent information to the eec.

Disconnect it, and any odd input will be gone. It should be hard to start when disconnected, but otherwise run fine. (power may be down, so no wot blasts) If it still runs odd with the Cam sensor disconnected, it isn't likely the cam sensor.


my question is what is true? I understand the cam sensor is required to start the car, so if your tach works fine and your car starts fine can the cam sensor be rulled out???
 
looking at the haynes manual and remembering some other posts i believe the cam sensor controls firing of the injectors, so i dont think its only used for start-up.

i think u can rule out the cam sensor. and if the crank sensor was going out i think you'd have more problems than mis-fire.
 
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The CAM sensor is used by the EEC to generate a signal used to fine tune fuel injection timing. It also supplies information on when the #1 cylinder is ready to fire.

If the CAM sensor is no longer providing any signal, the EEC will throw the computer into a guess when to start mode. Using the Crank cylinder, it will know when #1 is coming up, but it doesn't know if it is on compression or exhaust stroke. So the EEC will take a guess, fire one of the 3 coil packs. If the engine starts, it guessed right. If it doesn't start, the next time you key off, key on cycle, the EEC will take another guess on which coil pack to fire. After a few tries it'll get it right.

Then the EEC will set timing to a fixed value and let the motor run.

If the CAM sensor is providing a signal, and the signal is not consistant, the EEC will listen to it, and may make timing decisions based on it, allowing a flakey CAM sensor to dick with things.

I believe the Tach signal comes from the DIS input into the EEC. The DIS will provide a tach signal based on inputs. If the CAM sensor isn't giving one, it'll create a signal based on what it gets from the crank.

When a crank sensor fails, the EEC shuts off the engine. No if, ands , or buts. What this can mean though is if the crank sensor is acting up. Sometimes reading, sometimes not. The EEC will blip back and forth based on what it sees, either trying to shut the car off, or letting it run. That odd behavior of trying to shut it off, and letting it run is what can cause the misfire, and rough running when a crank sensor is not completely failed, or the harmonic dampner is moving around too much.
 
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