14 replies to this topic

[mattbuk85]

Hello,

I have a problem where my rev counter needle dances up and down for a few seconds, when this happens the engine stutters. I think it must be the crank position sensor but before I shell out £80 I thought I'd check on here to see what you people think. It idles fine and can go for miles without the fault occurring but when it does the engine almost dies. Anyone with a diagnostic sensor near Salisbury?

Many thanks for your help.


Rover Mini Cooper Spi '94, 89000 miles

[rick.spi]

got the same problem mate... does it feel as if its working against itself now and then?

[mattbuk85]

Yeh whenever the needle does a dance it looses power. The crank position sensor looks pretty easy to change, just want to make sure it isn't something else.

[Mattl]

Yeh whenever the needle does a dance it looses power. The crank position sensor looks pretty easy to change, just want to make sure it isn't something else.

My money is on the coil!

[mattbuk85]

Yeh whenever the needle does a dance it looses power. The crank position sensor looks pretty easy to change, just want to make sure it isn't something else.

My money is on the coil!

Ideal, connections? whole thing busted? What should I look for?

[Rosslin Racing]

could be conection look at them good clean them if oily and clean the coil as well. see if that helps if not change the coil for one you know that works if no joy then the sensor may well be duff

Edited by Rosslin Racing, 15 July 2009 - 07:49 AM.

[spiguy]

could be conection look at them good clean them if oily and clean the coil as well. see if that helps if not change the coil for one you know that works if no joy then the sensor may well be duff

Had the same problem recently on my '95 Spi cooper - turned out to be the crank sensor connections were corroded. Gave them a good clean up (both in the plug and the socket - you can unbolt the one attached to the engine for better access) cleaned them up with fine sandpaper. Sorted.

My car actually went from running, to not starting at all (for a day) to starting and running but spluttering everywhere, then when I came home with a meter, scope etc from work, seemed to be fine (typical). then later that day it happenned again - so while it was doing it, I waggled the connector for the crank sensor and it stopped doing it - good sign!

Also, if it is the crank sensor signal dropping out, then each time it happens the fuel pump and main relay in the black relay box, will switch off . So you could put your ear to the box and listen for the clicking of relays which are going on and off as a further clue. On mine, I can remove the cover of the relay module due to a previous repair, so I can see the relays operating.

But easiest check, waggle the crank sensor connector when its happening.

[mattbuk85]

Ah that makes sense, I wiggled the connector and it drove really well for ~100 miles then started playing up again. I'll have a look tomorrow evening and clean up the connections. Cheers!

[spiguy]

Ah that makes sense, I wiggled the connector and it drove really well for ~100 miles then started playing up again. I'll have a look tomorrow evening and clean up the connections. Cheers!

Hope it turns out well. Let us know the outcome.

Cheers
Craig

[mattbuk85]

Cleaned up all the crank sensor connections and the coil connections and tested the coil resistance. Still jiggered... I'm ordering a new crank position sensor.

[DaveRob]

The coil resistance alone wont tell you the answer.... Yes it may be that the sensor is FUBAR... but the coil is under a lot of electrical 'stress' It takes a lot of energy to generate those sparks.... consequently it also generates heat in the coil this is what causes coil faults..... that and the extreamly high voltages..... these cause insulation break down inside the coil..... an intermitant fault like you describe might only happen after some running so the resistance check is not the best way to test it. Without the right kit the easiest way is by substitution.... ie change it , or borrow a known good one... If you are sure the sensor connections are ok... i would move on to checking the coil first as the sensor is more likly to be ok if all the above advice has been followed... an intermittant fault is going to be hard to trace but at this point ... and reading all the above, my bet would be the coil.

Keep us updated

Rob

[mattbuk85]

OK, new plan, I'll take the crank sensor off tomorrow and have a proper look at it/clean up the sensor bit. If that doesn't work I'll get a new coil (only £25 and my one looks 100 years old anyway) then if that doesn't work I'll get a new sensor. (£85 ) At least looking at the wiring diagram it has to be sensor, coil or ecu so I can narrow it down a bit.

Cheers Rob.

[mattbuk85]

cleaned it up, made no difference, new coil on order...

[mattbuk85]

Yep coil it was. Thanks for your advice all, probably saved me making a mistake and starting with the sensor.

Cheers.

[Mattl]

Excellent. if only i could diagnose my own problems so well. lol