Author Topic: Why Did This Crank Position Sensor Fail?  (Read 2293 times)

Offline SmithSwede

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Why Did This Crank Position Sensor Fail?
« on: June 07, 2019, 07:19:34 PM »
My 2013 Stone would not start—no gas, no spark.  I fixed the problem by replacing the CPS on May 18 with a pricey $240 OEM sensor I bought from AF1 in Austin, with genuine Guzzi part number and label from Magneti Marelli. 

18 days and 1,179 miles later bike would not start as I’m trying to leave DFW airport at 1:00 in the morning.    :undecided:

Bike ran great the whole time before the failure   No signs of problems. Other than sudden failure to start.

I have now replaced the “new” OEM sensor with a $40 cross reference sensor from Latvia.  Bike started immediately and ran fine for 75 miles, running anywhere from 25 mph toddling on country roads to 85 mph blasting down interstate.   I’ve repeatedly shut bike off and restarted it.  Works fine.

So why did this sensor fail so quickly?  Was I just unlucky?  Infant mortality?   Some more fundamental electrical problem?

This is a 3 wire sensor.  Which I think means it is a Hall effect sensor that need 12 volts across two terminals, with the ECU sensing a signal from the 3rd terminal.   So I think it could be affected by overall electrical circuit of bike--it is not a merely passive, 2 wire sensor like on older Guzzis.

Just took voltage measurements at battery terminals. Engine off battery reads 12.98v.   Engine at idle gives 13.57 volts.  At any rpm above 2,500, I get 15.40 volts. 

So yes, that’s high.    But it’s been that way since I got the bike.  The first CPS lasted 50,000 miles, the second 40,000 miles, and the third 1,179 miles.  So I’m not sure the somewhat high charging voltage is the problem.

Thoughts?
« Last Edit: June 09, 2019, 02:27:28 PM by SmithSwede »
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Offline Daleroso

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Re: Why Did This Crank Position Sensor Fail?
« Reply #1 on: June 07, 2019, 07:28:53 PM »
I'm no help SmithSwede but mine failed at 53 miles on my new '17 Griso in March. Just luck of an electrical part? I now have 1K on post 1st service & beetle map. Fingers are crossed.
Best of luck🤙

Offline LowRyter

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Re: Why Did This Crank Position Sensor Fail?
« Reply #2 on: June 07, 2019, 07:55:39 PM »
cheap chinese parts or hidden electrical short/connector/gremlin?

Take the two failed parts and stick them in and see if the bike runs.  That way you'll know it's the CPS.
« Last Edit: June 07, 2019, 07:57:07 PM by LowRyter »
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Offline Wayne Orwig

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Re: Why Did This Crank Position Sensor Fail?
« Reply #3 on: June 08, 2019, 10:22:04 AM »
This is a 3 wire sensor.  Which I think means it is a Hall effect sensor that need 12 volts across two terminal, with the ECU sensing a signal from the 3rd wire.   So I think it could be affected by overall electrical circuit of bike.

Just took voltage measurements at battery terminals. Engine off battery reads 12.98v.   Engine at idle gives 13.57 volts.  At any rom above 2,500, I get 15.40 volts. 

They are all reluctance heads as far as I know. Basically, a coil of wire. The three wire version has a shield on the wires.
An ohmmeter to the sensor should tell you if it has failed.

Yea, that 15.4 volts will damage a battery pretty fast. Is that with a good meter?
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Re: Why Did This Crank Position Sensor Fail?
« Reply #3 on: June 08, 2019, 10:22:04 AM »

Online RinkRat II

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Re: Why Did This Crank Position Sensor Fail?
« Reply #4 on: June 08, 2019, 10:43:37 AM »

      I don't believe those see a full 12 volts from the ECU, more likely 5v. It would be interesting to get the ohm values of all three sensors to compare. MHO

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Online Chuck in Indiana

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Re: Why Did This Crank Position Sensor Fail?
« Reply #5 on: June 08, 2019, 10:48:10 AM »
From memory  :rolleyes: and my computer's udders up so I can't look it up, it should be 680 ohms. Wayne will know..
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Online antmanbee

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Re: Why Did This Crank Position Sensor Fail?
« Reply #6 on: June 08, 2019, 12:57:25 PM »
Yes they are 680 to 700 ohms. Just checked one this morning. Testing my spare for my up coming trip.

Offline SmithSwede

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Re: Why Did This Crank Position Sensor Fail?
« Reply #7 on: June 08, 2019, 04:56:18 PM »
Correct.   It should read 680 ohms. 

Of course, I already know that the two other sensors are bad, because replacing them immediately solved the problem.  What I'm wondering is what is killing them.  Is there anything I should be looking for?  Or just soldier on with the newly replaced sensor and see if it also fails in the near future? 

And yes--I don't know for sure that the sensor gets 12 volts, or 5v or whatever.   I'm just saying that I think it gets voltage across two of the terminals, with the third terminal sending a signal based on the Hall effect.  It's not just a passive, two wire sensor.   I'm assuming the 12 or 5 or however many volts is coming from the ECU.  But if the ECU is getting fed excessively high voltage, does that mean it then sends excessively high voltage over to the sensor?

I might try to rig up a way to test a working sensor while it's on the bike, engine running.   But I'm not entirely sure what I'd be looking for.   A steady 5 or 12 or however many volts between two terminals, and a fluctuating signal from the third?   Could I even see the signal with a multimeter?
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Online RinkRat II

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Re: Why Did This Crank Position Sensor Fail?
« Reply #8 on: June 08, 2019, 06:14:23 PM »
 
 If you have an old Simpson 260 or equivalent analog meter you could see the pulses, but with todays digital meters probably not. However if you know any Radio hobbyists with an oscilloscope you could check all kinda stuff. Just curious, did you ohm the bad sensors after failures?  Todays electronic components usuall have a pretty broad tolerance on voltages so I would think you'd have to be really out of spec to cook one and it would probably take out something in the ECU ahead of it.

      Paul B. :boozing:
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Online Kev m

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Re: Why Did This Crank Position Sensor Fail?
« Reply #9 on: June 08, 2019, 07:03:15 PM »
Just took voltage measurements at battery terminals. Engine off battery reads 12.98v.   Engine at idle gives 13.57 volts.  At any rpm above 2,500, I get 15.40 volts. 

So yes, that’s high.    But it’s been that way since I got the bike.  The first CPS lasted 50,000 miles, the second 40,000 miles, and the third 1,179 miles.  So I’m not sure the somewhat high charging voltage is the problem.

Thoughts?

You seem to have missed the part where a few years ago a bunch of us checked our charging voltage in response to it being noticed that Guzzi selected an unnaturally high output regulator and many seemed to be over-charging even by their bizarre spec.

I mean their manuals we're claiming up to 15V was normal (despite the fact that most battery manufacturers seem to disagree). But even Guzzi was saying that over 15V is too high.

So a bunch of us replaced our regulators with aftermarket ones that hold to a much more typical industry standard of ~14.5 or less.

Anyway is this related. I dunno. I've heard reports that some smallblocks overcharged enough to damage the ECU. But that's the ECU not the sensor and I think it was only on ones that were drastically over-charging.

So I'd still put that on the list to fix.

But I don't think that would translate into a higher reference voltage for the sensors because if it did I would expect sensors to return out of range signals that would cause diagnostic codes to set.



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Offline SmithSwede

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Re: Why Did This Crank Position Sensor Fail?
« Reply #10 on: June 08, 2019, 08:04:32 PM »
Thanks Kev.  Yes, I’m thinking why not fix the regulator problem.   What’s the go to solution for this?

And yes, I did check the failed ones.  Rather than 680 ohms, I get like 0.7. 

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Online Kev m

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Re: Why Did This Crank Position Sensor Fail?
« Reply #11 on: June 08, 2019, 09:28:45 PM »
Thanks Kev.  Yes, I’m thinking why not fix the regulator problem.   What’s the go to solution for this?


A bunch of us put on aftermarket Mossfet units (Jay, Cam, and I did four just among ourselves and I think s number on this board also used them).

We sourced from the internet, a motorcycle electrical specific website. I think it came up first page on a Google search for Mossfet style regulators.

I know we posted threads about it. But if you have trouble finding let me know and I'll search.
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Offline Kiwi_Roy

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Re: Why Did This Crank Position Sensor Fail?
« Reply #12 on: June 08, 2019, 10:37:27 PM »
Thanks Kev.  Yes, I’m thinking why not fix the regulator problem.   What’s the go to solution for this?

And yes, I did check the failed ones.  Rather than 680 ohms, I get like 0.7.

Thats surprising I thought they would fail open circuit, any chance of testing one again?
I wonder if the leads are shorting out.
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Offline Wayne Orwig

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Re: Why Did This Crank Position Sensor Fail?
« Reply #13 on: June 09, 2019, 10:14:58 AM »

Just a coil of wire.  Put an oscilloscope on it and crank the motor.
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Re: Why Did This Crank Position Sensor Fail?
« Reply #14 on: June 09, 2019, 10:48:12 AM »

 If you have an old Simpson 260 or equivalent analog meter you could see the pulses, but with todays digital meters probably not. However if you know any Radio hobbyists with an oscilloscope you could check all kinda stuff. Just curious, did you ohm the bad sensors after failures?  Todays electronic components usuall have a pretty broad tolerance on voltages so I would think you'd have to be really out of spec to cook one and it would probably take out something in the ECU ahead of it.

      Paul B. :boozing:
Yes, I have a Simpson 260 for atomotive work...Many modern digital meters, like my Fluke, will average readings that pulse or vary....CPS fail on cars and trucks for no reason,some last forever, some not... is there a cheaper alternative to the Guzzi part? Many sensors are universal for many different vehicles...like temp sensors on Ducatis also fit some Nissans....

Offline SmithSwede

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Re: Why Did This Crank Position Sensor Fail?
« Reply #15 on: June 09, 2019, 03:57:55 PM »
By gum, I *will* figure this out.     

I kept thinking that since this Magneti Marelli SEN813 sensor was a 3 wire sensor, unlike the older 2 wire passive, inductive sensors, that it must be a Hall effect sensor.  So I figured it had 2 wires supplying a current for the Hall, with the third wire providing the detected signal.  Which would mean since external voltage was being supplied, the sensor was part of the overall vehicle electrical system and might be effected by voltage spikes or excessive voltage due to the hot OEM regulator. 

So out came the Dremel and pliers, and I cut open one of the failed units.  Underneath the outer rubber covering of the cable is a silver metal sheath.  One of the wires is bare, and is in direct contact with this sheath along the entire length of the cable.  This bare wire goes to terminal #3 on the connector (#1 has a yellow wire and #2 has a red one).

Hmmm.  So the third wire is just some kind of coaxial, anti-static, anti-interference feature.  Ok. 

Sure enough, the cross-referenced Meat & Doria 87074 says this is an inductive sensor, not Hall effect.   Taking the dremel to the sensor unit revealed a magnet with a coil of very thin wires wrapped around it.  So I’m now convinced this is a purely passive inductive sensor, which leads me back to wondering why it would fail.   As a previous poster correctly said, it’s just a coil of wire.

Of possible significance is that the Magneti Marelli products catalog says the maximum operating temperature of these sensors is 125 degrees C, or 257 degrees F.   I wonder if this sensor routinely sees temperature above this “maximum” value on a hard run Guzzi small block.   

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Offline Wayne Orwig

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Re: Why Did This Crank Position Sensor Fail?
« Reply #16 on: June 10, 2019, 10:08:30 AM »
Hmmm.  So the third wire is just some kind of coaxial, anti-static, anti-interference feature.  Ok. 

Sure enough, the cross-referenced Meat & Doria 87074 says this is an inductive sensor, not Hall effect.   Taking the dremel to the sensor unit revealed a magnet with a coil of very thin wires wrapped around it.  So I’m now convinced this is a purely passive inductive sensor, which leads me back to wondering why it would fail.

Yep, the third wire is a shield to reduce electrical noise issues.

Above I believe you stated that a failed one was 0.7 ohms. Basically, it was shorted out. My guess has always been that the heating and cooling expands and contracts things enough that the wires rub and short out. Or the wires get pulled and break open.
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