A knock sensor detects early ignition within a cylinder during normal running and retards the ignition to prevent it. Someone will be along soon with a more techie answer.

http://wellsmfgcorp.com/pdf/counterp_v4_i4_2000.pdf

Early ignition, or detonation is an unwanted explosion of the air/fuel mixture in the combustion chamber caused by excess heat and compression, advanced timing, or an overly lean mixture. Detonation, or "knock", greatly increases the mechanical and thermal stresses on the engine. Also referred to as "ping" - although never heard anyone call it PING in my life!

When was your last service? Could be timing (and I wonder why you are asking about the above - is something suggesting that you have a knock issue?), plugs need changing, fueling etc.etc.... If you had a problem with the battery or altenator, you'd probably soon run out of power to start. Is the engine turning over normally?

 

Ive just had the Turbo replaced and the Exhaust took full force of the oil that poored into it, when it was plugged in to VAG it came back with the knock sensor and lamba sensor intermittent. the exuast was taken off to bet at the bolts etc on the underside of the turbo. I was just wondering if this fault has come up as there a lot of wires etc were the lambas are and was wonderibg if this is were the knock sensor was and it was not pushed on properly so i was just going to locate it to see if it was on or if its lose

As for starting the car when you turn the key it a low BTY type of start but when its running its fine then if you stop its the same nomatter how far the trip.

 

Pre-ignition or knock as it is now called, was always known as "pinking" as it sounds like a mettalic rattle or "pinking" sound. Us older generation have always referred to it as "pinking" Turbo engine req. a knock sensor because of the variable compression ratio.
H.

 

it runs great would Vag have picked this up because it may have been disconnected the version of VAG is the free stuff and we cant reset the DTS or Faults, so can i take it that if the car is running ok alls well or if it was a problem it would run like a bag of shit

 

Just had a think or is it me going mad if the ALT was buggered none of the electrics would work as the BTY only starts the car and if the engine is not running work the radio, lights etc is this correct.

the knock sensor is the main one at the moment.

 

Hi Graig, The alternator keeps the battery charged, so without the alt the battery would soon be discharged & the engine would fail to keep running, let alone start.
H.

 

Hi Harold just took the BTY off with the engine running (i know dont tell me shouldnt do it) and all seems fine the lights work etc BTY on and the samething..... starts just as if the BTY is flat....... i think its the original bty so its close on 6 years old i will try and put the 4x4 bty on it later and see if this kicks the engine first time, will this then tell me its the BTY or ALT. Surly if the ALT was buggered i would have nothing when the BTY was off.

thanks chaps/harold

Craig

 

Hi Harold just took the BTY off with the engine running (i know dont tell me shouldnt do it) and all seems fine the lights work etc BTY on and the samething..... starts just as if the BTY is flat....... i think its the original bty so its close on 6 years old i will try and put the 4x4 bty on it later and see if this kicks the engine first time, will this then tell me its the BTY or ALT. Surly if the ALT was buggered i would have nothing when the BTY was off.

thanks chaps/harold

Craig

Your best bet is to take the car to quickfit or a local garage and ask them to test the battery...

Quickfit did mine for free a few years back ...they may charge now tho :?

when you rev it do the lights on the dash or headlights get stronger and then fade really badly (Easier to check at night)

Get the bat check out...Im sure vag-com will be able to give you readings..someone may be able to advise what readings you should expect...

 

any other ideas chaps please

 

Hi Craig, Yes you should never disconnect battery, with engine running, but appears you have done no damage. Alternator must be O.K. (or was). Could be a dodgy battery or a poor connection on the battery or starter motor or a bad earth connection between engine & chassis.
H.

 

Hi Craig,

Very dangerous disconnecting the battery with the engine running - if there's no surge diode fitted (sometimes they don't bother renewing it on reconditioned alternators), it's possible to overvolt the system and blow your dashpod, ECU, ABS etc etc. :? Luckily you've got away with it!

The knock sensors are on the inlet manifold. Oil down your exhaust pipe can cause lambda damage. It might clear off once your engine is working properly. Symptoms of a dodgey lambda is inability to hold constant revs and cruise smoothly, poor mpg etc. Full power will probably be OK.

Poor starter performance might be a bad connection somewhere including a bad engine earth. Check all the big thick cables from engine to chassis and starter to battery. A bad connection will be hot with use. As suggested, KwikFit will test your battery.

 

thanks john i will see if i can sort the knock sensor and take the car to sort the bty out

 

on my to kwik-fit today to see if thay can sort the bty thing out.

 

Good luck

 

Surely its just time for a replacement battery? - 6 years old really is pushing it, most batteries lifespan is 4 years, mine is now just over 4 years old, and since its been 4 years old its gone downhill quickly. If i live the car for a few days it will struggle to start, and if i put the HU on without the engine running it'll last about 3 minutes!

I wouldn't even bothered messing around with testing, asking questions, taking it to kwik fit etc etc, just buy a new one, even if its not the problem it won't be a bad thing to replace a 6 year old battery and personally i would say its a 90% chance thats what it is. For the sake of the price of a tank of V-Power id go for it.

Can't help you with the other problem though...

 

thanks m8 the problems sound like its the BTY as it will struggle now and again to start up. Then other times it wont start at all, as if it will only hold part charge. I have just been out ond looked into each cell some are a bit lower than others and you gan see the top of one of the plates.

 

well been to kwik-fit and the BTY is total F--ked. big red cross in the machine, so asked them to replace it with a new one... And guess what they dont have any in stock in the Cardiff/Bridgend Area :evil: So if you see me in the next few days on the M4/A470 waving like mad please stop and give me a push

 

Hi mate, do you have any uprated ice (or plan to get any, sub etc?) if not - id just go for the best standard battery, i believe about £50 for Halfords?

Do a quick search on the forum for battery and the type you need will come up, its only a ten minute jobby swapping them around, i know they do a really powerful one for £80 but unless you want to run a bunch of stuff without the engine running for longer, or need more power theres not a huge need for it.

- D

 

Kwik-fit have said for the correct BTY £70, Halfords £91 and the standard BTY £54, am i right in saying here that any BTY will fit. I was led to belive that it must be the correct CCA (Cold Crank Amps) I think thats what he said must be used to turn the engine over.

Now iam confused :?

 

Not any battery will fit no, just do a quick search on the forum for the battery type you need, i dont know off the top of my head, or the manual will tell you.

The prices sound about right though, the standard should do.

 

Glad you got an answer on it there Craig . My battery is six and a half years old and still going strong - there's a big element with luck with the past history that determines lifetime - mainly how much it's ever been flat. At least you know it's not something else now