tommy_t

Have a bit of a broblem, perhaps....Today I was taking the on-ramp onto a highway and I just gave 'er. Coming up to the top of my 3rd gear I heard a rattling noise from the engine. It sounded like metal sort of clanging around. It doesn't do it when I'm just standing and reving the engine, just sometimes when accelerating at high rpm. Anyone have any ideas on what it could be? I'm going to try to record an audio clip to let you guys listen to it.

Davey G

It's called engine knock and it comes from the timing being to far advanced without running a high enough octane gas. Make sure you always use the highest octane that you can find and if you are using a power programer you might want to back the timing off a little?

dsmith678

Gotta love a car these days that requires high octane gas....$$$$

trbuddy

What you here is called detonation and is bad for your engine. You can blow a head gasket when this occours. It is either from to much advanced timing which would require a hgher grade fuel or you can retard the timing to get rid of it. The reason you here the noise is that it's getting to hot in the compustion chamber and the fuel/air mixture exlodes prematurely. As said very bad for your engine. Avoid the situation where it's doing it until you fixed the problem.

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tommy_t

Thanks guys! I'll give a higher octane a try.

Voodoo

I used to hear that noise on my T-Bird untill my muffler fell off.

neogenic83

how many miles do U have on the car. if U havn't advanced the timing it could be carbon build up on the pistons raising you compression which would require higher octane fuel

tommy_t

I have appx 35k miles...its a 99 gt

neogenic83

maybe you got a hold of bad gas.

Derf00

Some of the advice here is good, some is premature. Two things cause detonation, bad gas, or carbon build up in the engine. Three ways to fix it. The timing is electronically set on these cars so unless you have a flasher, it hasn't changed much..especially with only 35K miles on it. Older engines it's possible the timing chain tensioners/guides have worn a bit allowing extra play.

1) higher octane fuel - if you use 87 go to 89 if you use 89 go to 91. This is only a stop-gap measure meaning it's not addressing the real issue and will eventually come back causing you go up again in the octane ladder.

2) Colder heat range on the plug - helps the engine run a hair cooler, could use in combination with higher octane. Again, not addressing the real issue.

3) Verify the timing and have a shop do a decarbonization. This usually is done by running a really nasty, concentrated cleaner though the fuel rail directly through the injectors and intake. It removes the carbon buildup that causes hotspots. And no, running a regular fuel cleaner that you buy on the shelf won't work. The stuff the shops get is 20 times stronger and requires some specific automotive chemical license to purchase (I know because i've worked with shops and in service centers)

This method addresses the real issue. Carbon in your engine will heat up and cool down faster than the engine itself causing hotspots. These hotspots cause the detonation you hear. Get rid of the carbon and you fix the problem.

Easiest way to tell if you have carbon buildup is take a plug or two out. If they are black/sooty, you have carbon problems. If your tailpipes (either one) have black tips, you have carbon. Gas high in Sulfur (cheapy stuff) or oil getting into the intake throught he PCV system will cause this buildup. I know the V6 cars had a problem with this in 99-00 until they redesigned the intake baffle to keep oil from getting sucked up into the intake.

Add: ORRRRRRRRrrrr....it could be a loose heatshield around the catylitic converters. Vibration at certain speeds hits it just right and makes it rattle. Get under the car and check the cats.