Polo Pinking?

Err. A distributor is just a way of getting a spark to the spark plugs.

You _might_ mean carburetor, and in which case, the car could be single point injection, which uses something that _looks_ like a carb, but is just a metal thing with a throttle butterfly, and a single fuel injector in the place of the float chamber and jets.

Sometimes, "pinking" noises are actually caused by something small, metallic, and loose, rattling around somewhere.

Pete.

I thought injection was accompanied by electronic ignition, or am I completely off my nut?

Doesn't happen at high revs though.

Well, electronic ignition was around before most injection systems, and apart from some oddballs I'd say you're right. But plenty of cars had injection and a conventional mechanical distributor - it's just that there were no points, but some form of electronic sensor with an 'amplifier' between it and the coil. To get rid of the distributor completely means a mapped ignition system and more than one coil.

So is it pinking or not? :)

Some clues as to what to do with the car would be handy. I'll see if 97RON petrol helps in the meantime. Could lots of short, pootling journeys cause pinking?

Could well be that the head is coked solid - lots of short journeys will do that, and symptoms will include pinking, loss of power, poor economy etc. Once the layer of carbon gets thick enough, it will insulate the combustion chamber so that parts of this carbon coating will glow - this then ignites the mixture during the compression stroke (before the spark, hence the name pre-ignition), causing the symptoms described. If this is the problem, adjustments to ignition timing, mixture etc. will have little or no effect. Higher octane fuel may alleviate the symptoms slightly, but the only fix is to clean out the carbon.

Would I be able to tell by pulling the spark plugs out and having a look, ie. will the piston be covered in carbon as well as the head? I know giving the car a good high rev thrashing once in a while is seen as A Good Thing to keep carbon down, but is it a daft idea if it's this bad? I assume thrashing is better than driving around at low revs and pinking though...

Pinking is most likely at around peak torque or lower revs.

A coked up engine will have a higher compression ratio and therefore more likely to pink, but it's pretty rare these days. Optimax does seem to clean the engine, so you could kill two birds with one stone. But why not just get the ignition timing checked - this being wrong is the most likely cause.

There is certainly no harm in trying to take a look, but it's usually hard to see very much inside the combustion chamber without taking the head off in my experience. The buildup is usually worse around the valves than on the piston crown, so even if the pistons look clean there is no guarantee that the rest of the combustion chamber is OK. Have you taken a look at the plugs? If they have been in a reasonable time, they will give some idea of what's going on inside the engine. If there are really heavy deposits on the plug, assume the engine is going to need attention. Electrode or insulator damage would indicate that the problem is too serious to ignore. Let us know what you find.

AFAIK the plugs have been in for about 12 months, but that's probably only

Agreed that a coked engine is unusual these days, but should not be discounted, especially given a 'history' of short journey use. Since the demise of the mechanical contact breaker,ignition timing errors are also becoming things of legend. Time was when every DIYer had a timing light - doubt I would buy a new one now. The pre-ignition can be caused both by higher compression and 'hot spots' of glowing carbon - you don't need a huge amount of carbon, just a build up on one spot. As to cleaning the engine, whilst Optimax and other detergents seen good at clearing tarry or gum deposits on valves and the like, I doubt they will have much effect on carbon in the chamber - got to be worth a try, all the same.

Or there's the old 'pour some water in ' trick

the what trick??????? isnt puting water into an engine (well the bit where fuel goes) a bad idea???

as for my 2p's buy some redex and stick that in! has worked wonders for my car which only ever did short jouneys before i got it, 17yrs worth of short jouneys(it really did have one careful lady owner then i got it!!!)

later si

Had a mechanic ride in the car with me today whilst I made it make the noise. He reckons it's just a noise. Generally happens at fairly wide throttle openings at lowish revs. Any ideas? Something rattling around perhaps? I'm trying running it on 97RON super to see if it makes any difference, but as it's run so little it's not really worth putting a full tank in as it'll go off before it's used... Keep chucking in a fivers worth at a time for a while :).

Well it depends. If you pour in a small amount of water (although not that small, but you don't want to hydraulic lock the engine) to a hot engine whilst it's running it decokes the combustion chambers lovely. Or you can buy some hideously overpriced top end cleaner that does the same thing

This does work a treat. Hold the engine at about 3000rpm on the throttle linkage and trickle water out of jug into the inlet, enough to reduce the revs to about 2000 but not so much to hydraulic lock it!

If this engine uses a airflow sensor in the inlet trunking then getting the water in could be tricky as the engine wont run with the trunking disconnected!

Tim..

I can see this all ending in tears. I just hope he asks his mum first, before he explodes her Polo.

Right. The car's running on super unleaded and has had me giving it some welly this past week, and now it's stopped making the sound. So either the higher octane or the engine getting some revs or a combination of the two has sorted it...