What does a Crank Sensor Do?

[JohnDotCom]

I can't Sleep.

[GreyGhost]

My brain hurts.

[Departed]

Excellent info from Greeners there!

Ref another post.

Cam sensors are used on petrol engined cars very commonly. Older ones use a dizzy, yes, but these days most engines don't have wasted spark, but one coil per cylinder. So you need to know which cylinder is on compression, which exhaust. You struggle to get away with wasted spark on anything bigger than a four cylinder.

Prime numbers on the teeth, new one on me. But to have a number of teeth that divides into 360 degrees is helpful. Hence 60 as described by David.

Modern systems us a 'fast start' cam sensor. It has more than one tooth of different lengths. On a normal one you may have to wait up to two turns of the crankshaft before you 'see' the cam sensor tooth to synchronise. The fast start cam sensor can sync in less than half a turn.

[beededea]

Sorry to wake this thread from the dead but I have experienced what seemed to be an 'iffy' crankshaft signal in a 1990s Rover tomcat turbo.

It would start but not run, dying almost immediately after some attempts at trying to catch, all sensors replaced to no avail and in the end the 'iffy' signal was down to the signal cable.

It was lying in the loom against some other cables that carried voltage and possibly some significant amps and due to heat/cold/time their shielding had broken down. This had induced a current in the crankshaft sensor feed cable that led to a definitely 'iffy' signal. The sensor cable was good for resistance, wasn't open circuit, it was doing its job, the extraneous and intermittent voltage induced was enough to confuse the ECU and so the car just would not run.

Re-routing the crankshaft sensor wire independently to the ECU was enough to cure the problem but finding what the problem actually was took days of testing, changing components &c.

Just an addendum to what is a useful thread which might help someone trying to diagnose a non-running crank sensor problem.

PS. The Rover 220 turbo is no more, it succumbed to a multitude of faults, gearbox failure and a crumpled body after being spun... a pity as I really liked that car.

[frenchiejohn]

Hi. I am having strange goings on with my CPM. I had problems in Febuary this tear and replaced the CPM. Great - all OK. Two weeks ago, the car wouldn't start. Left it for 15 minutes, then it starts. Tuesday, Out shopping went to start the car in the car park and - zero!!! Had to be brought home. Now, I happen to have an extra rover 75, so I took the CPM off that and bingo all Ok. Then yeterday "here we go again"!!! Refuses to start. Leave 15 mins and it fires up. Get back home and it won't start! Take out the CPM, put it back into the other car and off we go!!!! What the hell is going on?????

[T-Cut]

Originally Posted by frenchiejohn

What the hell is going on?????

I'd say the sensor's magnet probe is losing its flux. OK when cold but not when warm is the typical symptom.
A suggested test is to remove the sensor when the engine won't start and chill it down in a frezer for 15 minutes. If everything's normal after refitting the cold probe, you've confirmed the problem. Fix is a new sensor.



TC

[frenchiejohn]

Thank you TC. I have a new sensor on the way. Thank you again.

[Kampo]

Originally Posted by Greeners

John

Chapter & verse


Crankshaft Position (CKP) sensor
The CKP sensor is located in the engine block, beneath the starter motor, with its tip adjacent to the outer
circumference of the crankshaft reluctor ring.
The CKP sensor works on the variable reluctance principle. This uses the disturbance of the magnetic field which is
set up around the CKP sensor, caused by the rotation of a reluctor 'target' attached to the crankshaft. The reluctor is
a steel ring with 58 'teeth' and a space where two teeth are 'missing'. The teeth, and spaces between, each represent
3° of crankshaft rotation. The two missing teeth provide a reference for angular position. As the reluctor rotates
adjacent to the sensor tip, a sinusoidal voltage waveform is produced which can be interpreted by the ECM into
crankshaft angular position and velocity.
The signal from the CKP sensor is required by the ECM for the following functions:
l To determine fuel injection timing.
l To enable the fuel pump relay circuit (after the priming period).
l To produce an engine speed message for broadcast on the CAN bus for use by other systems.
The two pins on the sensor are both outputs. To protect the integrity of the CKP signal the cable incorporates a
screen. The cable screen earth path is via the ECM. Correct CKP sensor outputs are dependent upon the air gap
between the tip of the CKP sensor and the passing teeth of the reluctor ring. The CKP air gap is not adjustable in this
application.
In the event of a CKP sensor signal failure any of the following symptoms may be observed:
l Engine cranks but fails to start.
l Engine misfires.
l Engine runs roughly or stalls.

I know this is an old post but i m trying to troubleahoot down a no revs issue coupled with e fan working constantly after starting. They may be unrelated but i figure cabling could be somewhere close between coolant temp sensor and crankshaft pos sensor and maybe rodents have got to them. However can i check if crankshaft pos sensor has issue can the car start still but show no revs at all?

[SD1too]

Originally Posted by Kampo

... can i check if crankshaft pos sensor has issue can the car start still but show no revs at all?

Marios,

If the crankshaft sensor signal doesn't reach the ECM (Engine Control Module), your engine won't run. If your engine starts and runs but the rev. counter remains at zero, the fault is not with the crankshaft position sensor or its wiring to the ECM.

Please see your other posts for my suggested diagnosis.

Simon

[Mike Noc]

Originally Posted by Kampo

However can i check if crankshaft pos sensor has issue can the car start still but show no revs at all?

If you mean the engine starts but doesn't rev then yes it can happen. Or are you saying the engine idles but the rev counter isn't showing any revs?

Usually the crank sensors are very reliable on the M47R, but if they aren't located properly, or you have an intermittent wiring fault the engine can start but won't rev.









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