355 cam phase sensor error symptoms

I can't say I've seen a gap value for the cam sensor, only the crank sensors (0.35~0.90mm).

Are you getting 12 volts in (with the ignition on)? A good earth to the engine block?

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Didn't realise your car was back on the road

 

If the ECM is giving you a code for cam sensor that means it’s not working with in a range limit or shorted -open or ground- depending

Because you see a signal doesn’t mean it’s good This is a DC square wave that will have a fix DWELL (% of on/off time) the ECM will only read the “on time” when the voltage from the sensor goes above a certain voltage usually on a 5v system it can be 3.75v and 12v system can be 10.5v and off time will be below that value the more gap you have between the sensor face and the tune ring of phaser effects the signal strength
the sensor itself creates a small magnetic field which is then pulled down as the teeth of the tune ring pass it basically switching it on and off as they go by
You will see a signal but by removing metal from the face of the ring you opened the gap now the sensor might only see a smaller amount of on time “aka DWELL” because the further away the sensor is from the ring the harder it is to be pulled down ( think of it like this — further away a metal part is from a magnet there is less forces on the metal as you get closer the more it gets pulled to the magnet) and this is what happens with the sensor and tune ring (aka phaser) are working the high points pull and low points release the magnetic field making what you see on the scope
And can put a check engine light on being you have access to a scope take another reading and compare to a known good car






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Yup, his car is back on the road and he now knows how to use an Oscilloscope.
Taz, fuzz on the signal means you have a dirty ground. Make sure you clean up that ground right below that sensor.

 

How Hall Sensors work:



Looking at the WSM, the output is a 5 volt square wave, so I assume the Hall Sensor converts the 12 volts from the ignition to 5 volts.

In the video, you can see a Schmitt trigger converts the signal to a square wave (@ 2:26). I assume the electronics in the sensor clean up the signal in the digitisation process, but you probably still need a good earth. Make sure your oscilloscope lead connections aren't causing the fuzziness.

 

It's the main engine ground on the back of the engine. Check continuity between the cam sensor connector and this ground.

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There are splices between the cam sensor connector and this earth.

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The actual wording is "The timing sensor is supplied by the ECU at 12 volts".

12 volts in, but the graph should be correct. Remember that there are electronics inside the sensor for processing signals/outputs.

Actually, that description is a little ambiguous. When the ignition is turned on, the Motronic ECU triggers relay "M" and the relay supplies battery power to the sensor.

 

Sounds like a ground or connection problem. Consider that the magnitude of the voltage is only effected by the gap on one branch (top or bottom voltage). So if there is noise on both branches it's not likely related to the gap.

 

My explanation above is a generalization of how these sensors work
Bosch is one manufacturer used to-make the system for ferrari and other manufacturers and tune ring is a term used for the Target that the sensor reads the amount of “teeth or points” vary there can be just one or more it’s when they come close or have a opening to the face of the sensor is when the sensor sends a signal to the ECM giving you the wave form
And the voltage used can vary too depending on the systems manufacture
Either way taking metal off and increasing the gap from sensor to target can effect the reads and drivability the ECM uses the cam and crank inputs to set ignition and fuel injection timing
I would try to find what the gap clearance should be or recheck with the scope on a known good car and change of just 500 millivolts can be a big Factor to your drivability problem



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I reiterate, stated a little differently. The sensor is basically an on/off switch between 2 voltage levels. Only one position is effected by the gap. So if there is noise on both the on and off signals it is not likely related to the gap. The first thing necessary is to find the source of the noise. Is it in the signal or is it in your measurement system? In either case noise is likely a bad connection somewhere. Also, what are the voltage levels you measured? WSM isn't clear.

 

I'll take back what I said about the WSM graph being correct....

The WSM has two different graphs (2.7 and 5.2 versions). This doesn't make sense as they have the same sensor and same supply voltage.

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How do you get 17.5 (?) volts out of a 12 volt sensor?

 

You get it in Ferrari manuals. I think the graphs are not accurate ("not to scale"), shown just to illustrate the shape of the output signal, i.e. show that it is on-off. It should be from 12V down to zero and back to 12V. In any case, it cannot be more than 12V.

In the case of the 348, the manual is clearer - it states that the ECU sends 5V to the cam sensor and the graph shows switching (square wave) between 5V and 0V.

Since the 355's sensor gets 12V directly from the car's wiring, the ripples shown by the oscilloscope on the top and bottom horizontal lines could simply be caused by the ripples in the 12V supply caused by the alternator and should not be the cause of the issue with the ignition as it is only looking at the "big picture" - the change from "on" to "off" from the sensor.

 

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Here is a scope pattern of a 12v power in 5v signal out Hall effect cam sensor at start up

Purple trace shows a steady 5v on and 0v off after the first crank cycle

Blue trace is 12 v supply you can see that at start up the 12v drop as the sensor build up its magnet field then 12v was ineffective by the sensor operation

This sensor has a gap of .7mm —-spec I was given is .5 to 1.5mm I got this spec from a f-tech (do not see it in any manuals) he pass the info to me and said that they sometimes pull the sensor to see if the face are damage telling them the there is to much cam bearing play again this word to mouth and I check it with my own scope and pull the sensor to look but never seen any damage to the face of the sensor



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This shows that, in the case of the 355 sensor, it is supplied with 12V but it has an internal step-down to 5V which is then switched 5-0 V. If the sharp drop in the blue 12V line on the scope coincides with the engine cranking, then it could be the result of the battery voltage drop when loaded by the starter motor.

 

I would say yes but if you notice that the sensor is reading the target as soon as the engine is being started meaning the magnet field was trying to build as it was being pulled down
That’s why there is a small and clear spike in both signals at the same time once the field is built it reads the rest of the target as it should and battery voltage started at around 12.6-12.7 drop to 12.1 to 12.4v (I only cranked the engine over till I got the trace did not start it)
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This is a zoom in image and yes that is probably the starter draw dropping the voltage down to around 7v for about 1.812ms on the power supply voltage
And on the 5v signal you can see the sensor starting to work right before the voltage drop that is in time with what should be the starter draw

I never went that far into the wave pattern and the time that this is happening is so fast
I would be looking at the 5v on time to see if the voltage goes into the time frame and voltage limit that the ecm will see as (on) by having a lager gap between sensor and target will effect that
there’s really no book to show what is right pattern is but by looking at known good he can see if he change the way the sensor is reading and possibly be his problem
Being he has access to the right equipment to check it it will only that up his time and not money throwing parts at the car






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Ahhh. That explains it.. when I saw the first trace I was going to say that your alternator wasn’t charging!

 

[EDIT: Mark, I see you beat me to it. ] >You simple don't have sufficient time resolution to see what is happening in that initial spike. It is most certainly related to the voltage pull down due to engaging the started. I can not see this being related to the variation in the magnetic field the Hall element is exposed to as that is due only to mechanical effects since the sensor contains a permanent magnet. Thus, if the engine is rotating the sensor sees the same filed variation regardless of supply voltage. What changes with voltage is the current flowing through the Hall element, hence the output voltage of the Hall element. Additionally, the behavior of the amplifier and Schmitt trigger would be effected by the supply voltage spike.

 

I looked up the spec on the sensor part# Bosch 0232103006 and this sensor is not a inductive (aka permanent magnet sensor) this sensor needs battery voltage to create the magnetic field and in the spec sheet gap is between .2mm to 1.8mm air gap and is a True Power On meaning it needs voltage to make a magnet field
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I trying to find on Bosch website if there’s anything about the input spec for the ECU
This will take a little time

But I would really like to know what the problem with the car is we have gotten off base and hopefully taz will share his findings


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