Rev counter jumping.

[dr_mat 0]

Anyone else seen this? I suspect it's some sort of voltage regulation thing, but a couple of the needles on the dash are jumpy from time to time - the rev counter being the most obvious. It'll wander along looking quite normal then it gets jittery .. then it jumps way up .. then comes back to normal. Doesn't seem to match engine or electrical loading, so I suspect something's loose .. any thoughts?

I tried the search but nothing came up ..

[Stonejag 10]

Have you got Vag-com? Mine did this for a few weeks before my crank sensor died - most pronounced at around 30mph. You may see an 'implausible signal' code stored if you check it.

 

It only did it when hot, but if it's your crank sensor the slight misfire / rev counter wander will suddenly turn into wild swinging between 0-4000rpm, firing at random intervals, backfires and your catalytic converter being shafted by all the unburnt fuel. It's a £100 part and half an hour to fit but a week of trauma if it goes suddenly..!

 

This was a VR btw, not sure of your model or if it works the same on all models...

 

Stone

[dr_mat 0]

Yeah, mine's a VR. Interesting. The engine doesn't run badly, it doesn't seem to be misfiring. I do have a VAGCOM cable but I suspect I can no longer find a laptop with the requisite serial port so time to get fiddling with stuff..

It did it yesterday on a cold start when the car hadn't been used for some time so it may be related I guess..

Thanks for the suggestion - makes sense, so I'll see if I can check it out!

[James. 7]

Second on the CP sensor.

 

Had exactly the same issue on mine.

[dr_mat 0]

What's the latest advice on sourcing a replacement? Just go to VW and stump up huge amounts of cash .. ?

[dr_mat 0]

Anyone have any idea why there's THREE crank sensors available from ECP .. ?

[craigowl 0]

dr_mat

 

I bought this one in Sept 2012. Never used it as autoelectrician established problem was ecu, which I replaced.

I am sure my man said they were reasonable brand.

I can send it to you for nowt - you can try it - if it works send a beer voucher - if not, keep it. No use to me now.

regards

Iain

 

http://stores.ebay.co.uk/All-Cars-All-Parts-Ltd/All-Cars-Shop.html_?_nkw=290653615231&submit=Search

[dr_mat 0]

That's very generous of you Mr Owl, so I'd be happy to give it a whirl. I'll cover your postage at least! PM on it's way. :)

[Stonejag 10]

Pretty sure my garage said they were obsolete from VW now, but the replacement was ~£100. I wouldn't go for the cheap ones just because of how dangerous it is when they go suddenly...(mine went at 90 on the M20!)

 

It's only half an hour to fit so really not that traumatic at all. But please replace it before it starts destroying stuff! My exhaust blow got a lot worse after it was backfiring everywhere...

 

Stone

[dr_mat 0]

Many thanks to Iain, I've now got a replacement sensor ready to go in. :)

I also got a USB vagcom cable so I can check ECU error codes. Last night the crank sensor wasn't showing any faults, but you need to catch it before the ignition is turned off otherwise the error code is overwritten. I'll do that, then arrange to swap the sensor.

Thanks all!

[Stonejag 10]

Be aware - if it's dodgy it may only misbehave when (very) thoroughly warmed up. Even after mine had gone on the motorway, it took 45 minutes of idling it on the back of the recovery truck before it was warm enough to start the revs jumping, and it still didn't throw a code at that point. Just replace it and see if it stops doing it in the next week or so :)

 

Stone