XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

Crank Position Sensor Problem Or Not?

 
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Old 05-13-2019, 11:00 AM
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Default Crank Position Sensor Problem Or Not?

Long Story Short:

As I was driving my XJS down a long dual Carriageway in the pouring rain, the Alternator Belt decided to Snap, at which point all hell broke loose as the Engine then cut out just a few Seconds later

Though luckily I managed to take a turning to the left and got out of the way of other Traffic, where on closer inspection I could see the Alternator Belt had Shredded like strands of Candy Floss

Where these Strands of Broken Belt had then wrapped themselves around the Crankshaft Pulley, which then had me thinking that they had cut off the Signal from the Crank Position Sensor in some way

So today I removed the Crank Position Sensor and was sort of hoping to find that it had been chewed up, where accept for being greasy, it looked in good condition

My only real concern about this was the gap behind the Crankshaft Pulley was looking very shiny as too were the Teeth on the Realtor Wheel which also looked very Shiny as if the Broken Belt had polished them up

There were no extra shims to adjust the Gap on the CPS but was wondering if a bit of grease could interfere with the Signal

Any ideas on what could be wrong



The Crank Position Sensor prior to removal with the New Belt



Crank Position Sensor Fixing Bracket: Note the Shiny Tooth of the Realtor Wheel
 

Last edited by orangeblossom; 05-13-2019 at 11:02 AM.
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Old 05-13-2019, 07:45 PM
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Inspect the tip of the VR sensor for damage caused by the belt. Post a photo

Check the gap it should be 0.020", the shredded belt may have bent the bracket. There is no adjustment on the bracket you need to elongate the holes with a file.

Oil will not effect the VR sensor unless it is contaminated with steel filings.
 
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Grant Francis (05-13-2019)
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Old 05-14-2019, 03:54 AM
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Hi Warrjon

Something I forgot to mention that maybe could have a bearing on what happened

This was no ordinary Rainstorm, it was really hammering down and possibly the worst I've ever seen

The Windscreen Wipers were on to the Max and so was the Demister for the Windscreen, where I would imagine that all of that might well have put a Current Strain on the Alternator, which caused the Belt to Snap

While at the time maintaining that very high current draw, which 'Could' have pulled the Battery down so much that the Engine Cut out

Just a Wild Guess really but you never know, although you might

Hard to get a Photo of the VR Sensor Tip, as the light wasn't right but will try again later if/when the Sun comes out

Although having said that from what I could see the Sensor looks undamaged although I could be wrong

So meanwhile I am planning to put the VR Sensor back having first cleaned it up, then giving her a Spin an see what happens and then I will report back

Thanks for your help
 
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Old 05-14-2019, 04:01 AM
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My alternator failed over 100km from home on a rainy day, not enough power in the battery to start her up, I got a jump start and made it home.

Give it a try and see how you go.
 
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Old 05-14-2019, 04:29 AM
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Hi Warrjon

That is interesting!

As if that can happen to you it can happen to anyone as what you don't know about Car Electronics, you don't need to know

So I will give it a Shot and see what happens and with a quick edit, I'll also add in that the XJS Windscreen Blower/Demister must suck up an awful lot of Juice

One of the Best demisters, I have ever seen on any Car
 

Last edited by orangeblossom; 05-14-2019 at 04:33 AM.
 
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