I have a question for the experts! I was talking with friends about cam sensors and I am being led to believe that at times if a cam sensor is failing it could cause the car to shut down while driving rendering it inoperative. After it cools down the car will start and run till the sensor fails again.

The question is could a failing crankshaft position sensor or an engine position sensor or a poor connection at either device cause the eng shut down problems we are seeing?

 

On my Jeep Cherokee a crank sensor failure (which is fairly common) definitely will cause a stall or no start condition.

I suspect this is true for at least some other cars, but not necessarily all. Not really sure on the Jags.

 

It definately can shutdown the engine, there is no doubt, but I would guess this would be a rare incident as the device as such seems to simple to malfunction. I have also no idea how they will disfunction, like if it can be temp related or not.

 

Electronics can definitely overheat, fail, then start working again as they cool down. That said, it generally only happens for a little while, and it will continue to get worse.

Under hood electrical components like ignition coils/modules are frequently at fault for cars without multiple coil packs like the XK series, but with the multiple coil packs, one failure shouldn't cause a no run.

Fuel pumps failures are many times consistent with the problem you're describing.

I always take it to the basics.
Air (MAF?)
Fuel (Fuel Pump)
Spark
Timing (Camshaft Position Sensor?)
Compression

It's easy to eliminate compression, and I think it's probably safe to eliminate the components that generate the spark.

That leaves you with Air, Fuel, and Timing.

I'd be listening to the fuel pump when you try to restart the car after it dies to hear how the fuel pump sounds or if it sounds. Usually a failing pump will emit a different noise.

You can try to diagnose a MAF failure using a pretty simple technique while the engine is actually running. MAFs that are failing will often have some issues if you tap on them lightly with the back of a screwdriver while the engine is running.

The camshaft position sensor would be suspect as well, but I don't know of any quick check for it.

 

The sensors are nothing more than a proximity switch, very basic, but obviously can fail

And cheap and easy to replace and yes without them the car will be a no go, it would be like a rotor arm without a drive key, timing will be all over the place

 

XKRacer, tap on the MAFS????are you friggen nutz???You hit it with a hammer. you just have to KNOW the right spot

 

If in doubt give it a clout

 

Gus, many position sensors become temperature sensitve as they age. They fail when hot but work well when cool again. I carry a spare set in my V12 XJ-S because it is such a common problem for those cars.

Measure the resistance of the sensor when it is cold and then again as soon as the car stalls. If there is a big difference, the sensor needs to be replaced.

If there is little or no difference the problem is somewhere else.

 

I asked this question for several reasons but the first and at this moment the most important reason is a possible cause for the recent engine stalls we are seeing could they be related to the position sensors. Could we be looking in the wrong direction? I am not sure and I wanted to see what other input I could get.

 

XKRacer said this is just a proximity switch. Switch means open or closed. Doesn't that me you can either short it, or open it, to get the car to start?

 

That is the way I see it.

 

Never mind, I just answered my own question. The computer needs to see a fast series of open and close in order to allow the engine to start. Is that correct?

 

Yes that is correct

This why there is a lump of metal pressed into the end of the inlet cam on bank 2

And the timing ring on the back of the fly wheel has holes followed by a extended hole so the ECU knows the position of everything, get one of those wrong and the engine will not work/run

 

is it a sharp cut out? like turning the key off? Or does the engine die somewhat gradual, like running out of fuel, notice the tac when the engine dies, if its a crank sensor you can see the tac drop instantly and the engine stalls, a crank sensor will cause the engine to stall where a cam sensor wont.. and if its a gradual die out, i would look at fuel, Good luck hope this helps..

 

This is a fact finding mission I presently do not have a problem. However, your info on the stall or gradual die is one I did not think about.

 

The fact for information a cam sensor will cause a no start, but if it goes intermittent open while the engine is running will not cause it to die, it will go into limp in mode and run with the ECM's default values.... just figured i make it a little clearer on sensors. Thanks Chris

 

> ... proximity switch.

No, it is an inductive coil which is why I mentioned comparing the resistance when cold vs hot enough to fail.

Proximity switches need a dedicated magnet to activate them, e.g. distributors with a ferrite wheel. Proximity coils are activated by the changing presence of any iron.

Proximity switches don't work well at high frequency, e.g. flywheel teeth, whereas the coil doesn't care what frequency it measures.