Hi,

I need help from some 2.4L guru.

My car is a 1999 Sunfire GT convertible, with 153,000km (95000 miles), 4 speed auto.

It runs fine, no problem starting hot or cold, acceleration is great.

But when it's idling, if I give it a slight sudden push on the accelerator, I hear knocking. It's worse when the A/C is running. It will knock for half a second, just as the accelerator was pushed, and otherwise it never knocks (appart from when starting, when the engine revs a little it does it once).

Also, and I don't think it's related, when the engine is hot I sometimes hear a rather loud metallic noise, it's like something is rubbing.

You can hear the knocking in this video:


And the metallic noise in this one:


Thank you very much!

After some research I think I found out the metallic noise, it's the a/c clutch. There's some metal shavings down there, and when the a/c is running the noise stops.

Before replacing it I would like to try increasing the air gap between the cluch and the pulley. It's supposed to cure the sound for good (or at least until the bearing or the compressor dies). Has anyone here tried to do this adjustment and did it cure the noise?

Since it's a convertible we don't use the a/c, so if this doesn't stop the noise I'll probably just go with an a/c delete pulley.

Thanks.

For the knocking/pinging sound, could it be related to spark plugs? Because it began after I changed the oil, oil filter, air filter, and plugs.

I installed platinum plugs, could it be that they're not compatible with the GM ignition? I kinda remember something I saw somewhere about GM engines being finicky with plugs.

Thanks!

So, over on the pontiac forums someone suggested that the timing chain tensionner might be bad. Now that I'm thinking about it the rattling noise does sound like a chain rubbing on metal.

If the timing chain is loose, is it possible that suddenly revving it up cause it to fly a little off and rub on the surrounding metal?

I'll keep you posted if I ever found out what's the problem.

You just installed spark plugs? Did you torque to correct specifications? If you over-tighten them the piston will hit the plug. You can easily rent a torque wrench from ORileys or Autozone for free. If it's the timing chain they say you'll hear it when you turn the car off and then hear that noise. Check your spark plugs first.

I checked the spark plug gap, and it was ok. If the piston was hitting the spark plug, the electrode would have collapsed.

But I found the problem.

While I was working on adjusting the a/c compressor clutch (which cured the metallic noise) I removed the accessory belt.

I started the engine without the belt, and to my surprise the noise was gone. I then installed the belt and the noise was back.

It was clear that it was coming from either the alternator, the tensionner pulley or the compressor. It couldn't be the compressor, because when the clutch is not engaged it doesn't even turn.

Having this info I was able to pinpoint the noise, and I'm positive (and my girlfriend concurred) that it was coming from the alternator.

I already ordered a new one, and will change it this week.

I'll also have to change the radiator fan motor, the engine temp was going up in traffic and I checked the fan and it doesn't work even with a/c on. Checked the relay (by swapping it with the heater blower) and it's good. I tried whacking the motor hard and it started, but when it's stopped it doesn't start up again.

And now I have a coolant leak from a hose behind the engine, just below the exhaust manifold.

I hope it's the last problem for a while, wish me luck!
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