ive had this problem for a while now and worked out the exact pattern for what it does but cant be sure whats causing it.

basically the car runs like a dream most of the time, but about 5 minutes into every journey i lose the speedo. this lasts for anything between 10 seconds to 10 minutes. to begin with i didnt take much notice of it but now its started causing other problems, all these faults only happen when the speedo is not registering. first problem is that when changing gear or stopping it has a tendency to cut out, very much like when the icv fails. and the other problem is when lifting off the throttle the engine kicks like a b*tch, its a huge jolt, i assume like if an engine mount had failed.

my theory is that its the vss at fault, but cant understand how that would link to the other problems? but they do seem connected because they all only happen together. is there something that could block/lose the signal from a selection of sensors all at the same time? a fuse/relay/ecu anything?

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

The battery is new so should be ok. Loose earth/connection i hadn't thought of. Would that not affect everything though?

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

Are the earth points easy to find? It's something I've never looked into before so have no idea where they are

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

That's what I was hoping to hear, I just wasn't sure whether the ecu was that clever. So the kick when backing off, would that be because it's expecting it to drop to idle so cuts fuelling?

I will replace the vss and hope that that solves it, if not then I will check the earths.

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

now it feels very sluggish too, although i dont think its to do with this fault.

anyway, i tried chasing the earths around the engine bay and found something that could be suspect, i think this should be connected to something but what do you guys think? its just above the gearbox and can be seen when looking between the battery box and engine, and a word of warning, that hose to/from the radiator is bloody hot lol (apologies for the poor quality pics) first pic is looking from over passenger side wing, others are from front

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

thanks Stan.

there is a bolt, i believe its m8, on the gearbox near to where that is and it appears to have a thicker black cable and looks like a ring connector in it? would the earth cable go onto that same bolt or should i try to connect it somewhere else?

im guessing this could very likely be the cause of my problems then?

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

oh so the negative from the battery will be the thicker black cable, so i need to find the other one.

will it still be ok to drive? i assume i will just have the same problem as ive always had, it wont get any worse will it?

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

looks like i could be going out tomorrow to get some electrical tools then, i did some wiring when building boats a few years back so know roughly what im looking for. am i right in thinking its wire strippers, crimps, and ring connectors to fit m8?

glad i got that right i like things like this to help me learn a little more about the car

EDIT halfrauds have their ring connectors marked with a max amps, am i right in thinking that doesnt matter on earths?

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

this sounds identical to my issue, i just put it down to VSS but going to check the earths tomorrow. it'd only a little ring connector on the top of the box, piece of p*ss to fix. doesn't matter as it's only earthing but make sure both contact points are clean

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ok thats good, thanks

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

It may be a week or 2 though, I've switched to nights at work 5pm to 6am so will only really have time for work and sleep. And I'm hoping then I can get the car to Miles to get my suspension built so will probably get him to do the earth and vss at the same time, that would then eliminate both as possible causes. Just for curiosity purposes though I may ask him to just do the earth first and then road test to see if that solves it, then we can have a definitive answer to this thread

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supercharged China gti6 - Thu 16th Sep 1999 - sold
2010 megane rs250

i also have this fault intermitentlly,will check my earth to, plus what does vvs mean?

I have a similar issue with the engine jolting sharply on transition from revs to idle. Kind of feels like its all or nothing. Also the engine judders on over-run. Im still on with getting to the bottom of it when i have few minutes spare. The speedo on mine will very rarely stop working but the above faults happen all the time.