Cooler plugs to prevent pinking?

My 2003 Fiesta Zetec sometimes makes a rattling noise when accelerating. Oddly, it only does it in one particular place each day, after it's been running for about 2 or 3 minutes. There's a stretch of road a few minutes into my homeward journey that is slightly uphill, and as I accelerate up it in 3rd, the engine starts rattling. It doesn't stop me accelerating, though. After that, I don't hear it any more, so it might be temperature-related. I was wondering if I might use cooler plugs to see if that shuts it up, but don't really want to waste money if it's not going to make any difference. But does it make sense to even try this approach in the first place? Would cooler plugs actually make a noticeable difference if it /was/ pinking? And isn't there a knock sensor that's supposed to prevent this?

Reply to
Etaoin Shrdlu
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more likely a rattling catalytic converter.

Reply to
Mrcheerful

Would that show up on the MOT readings? It's been doing this for years.

Reply to
Etaoin Shrdlu

Pinking is mostly cause by too much ignition advance for the combustion needs at that particular load. Can be caused by carbon build up making the effective compression ratio higher, or the mixture being too weak. Or any combination of the three. On a standard engine, I'd be surprised if changing the plug grade would fix it.

Reply to
Dave Plowman (News)

Well, I dropped an endoscope in a while back, and there is certainly carbon build-up. If it's more than normal, though, I couldn't say. I'm not sure how I could check the ignition and the mixture, with them being computer-controlled. Plugs look okay, although they get changed often, so they might not be a good indicator any more. I've a feeling that plugs need a few years carbon build-up before the colour can be used as an indicator.

Reply to
Etaoin Shrdlu

No. A rattling car is as likely to just be the external heat shield come loose as the actual internals.

Reply to
Adrian

That should be a rattling caT, of course.

Reply to
Adrian

I took out half of the catalytic converter element on a ford escort, it still passed the mot. As adrian said, it could just be the heat shield, but a rattle from the cat is quite common and often goes away as it warms up, get under the car when cold and have a thump about, you will soon hear if the cat is rattling and where from. Pinking is very unlikely when the engine is cold in any case.

Reply to
Mrcheerful
[...]

The mixture and ignition timing are constantly changing in an ECU- controlled engine. There is no realistic way of either checking them, or adjusting them. In any case, if anything was seriously awry it would not pass an MOT emissions test. A failure would occur long before an out of spec mixture could be detected by plug colour alone.

The 'fault' you are describing is so trivial that it might be a case of 'they all do that sir'. The other thing to bear in mind is that it's a 12 year old entry level car, so it's unlikely that it would perform absolutely faultlessly.

Just drive around the problem. Try using a different route home, for example, or tackle the hill at a higher or lower speed.

Chris

Reply to
Chris Whelan

It does sound like that heat shield, but I've tried jiggling it about, and it seems solid. Unless there's something else in the vicinity, or trapped underneath it? I think I'll take the top cover off and have a closer look.

Reply to
Etaoin Shrdlu

Well, it's been doing it for years, with (apparently) no major side-effects. I'm probably not going to take the cat off and shake it about. I did try thumping it with a rubber hammer from underneath, but wasn't able to make the same noise.

Reply to
Etaoin Shrdlu

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