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I have 99 SEAT Ibiza, which was until quite recently owned and driven by my mother. It's therefore been well cared for, but was hardly ever given a good run or allowed to get warm. On its last major service - which was early this year - the oil was a suspicious colour which the guy said can warn of head gasket failure, but given the treatment it's had, he figured it was more likely to just be residual moisture that hadn't been given a chance to cook off.

Anyway, for a few weeks I've been noticing a light tinkling sound coming from the engine bay when accelerating. I change gear early for reasons of economy, and being a fairly new driver I don't always time it right and the engine can struggle under load. The noise is most noticeable changing from 3rd to 4th at around 2000rpm then applying some firm throttle.

From the information I have and what I've read, I suspect engine knocking or misfiring. Detonation due to dirty plugs would fit the treatment it's had previously - short runs would tend to cause crud buildup, or so I gather. A friend has offered to help me inspect the distributor cap and spark plugs, but is there anything else I need to be aware of or look for?

edit #1:

Thanks folks. Taking advice, I've gotten into the habit of leaving the gear change til later - usually 2.5 to 3k, and the problem has pretty much disappeared.

I've also taken to giving it a blast up to 5k RPM when joining the highway each morning to clear away the cobwebs...but we won't tell anyone about that, will we?

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First, I think you're changing gear way to early if you're changing up from 3rd to 4th at 2000rpm, especially when the engine is under load. There's a reason the redline is higher than that :). You're not really doing yourself a favour with that, and neither are you doing the engine a favour.

Knock or pinging is usually caused by the fuel burning uncontrolled and at the wrong time.

There are a couple of problems that can causing engine knock/pinging:

  • Wrong or dirty spark plugs
  • Ignition timing off
  • Mixture lean
  • Using fuel with the wrong octane rating (too low)
  • Too much load on the engine for the rpm
  • Deposits in the combustion chamber that heat up to the point that they can ignite the air/fuel mixture

I think giving the ignition a service (ie, new plug, distributor cap and rotor if the engine still has one of those, plug leads of those look like they're original) is a good starting point.

Also, if it hasn't been changed I'd change (or have someone change) the fuel filter, these fill with crud over time and if it's partially clogged this can reduce fuel pressure and cause a lean-ish mixture. I'd also run some fuel system cleaner through the tank (or use a tank or two of something like Shell V-Power that has additional cleaning ingredients) and take the car out for a good run outside of town.

Don't be afraid of revving the engine and driving it hard(er) (aka the "Italian tuneup") as you want to make sure that everything gets up to operating temperature and possible deposits get a chance to burn off.

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Thanks for your help. I've had the distributor off with some help, and the contacts and rotor both looked pretty worn. I'll be acquiring a new cap, rotor and leads shortly so we'll see whether that silences the rattling. –  Tom W Sep 21 '11 at 13:27
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That is probably knocking, or premature detonation. It's a little hard on the motor. It's likely that you should be in a lower gear or ease off the throttle whenever you hear it. It is probably normal for that car. Higher octane gas might help, but it's not good for the car to drive in too high a gear.

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