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Discussion Starter #1
My '97 4.6L bird makes a rattling noise when under WOT. The noise sounds like it's coming from somewhere around the transmission. Is this a common problem, and can anyone tell me what it is? Alternatively, could someone suggest how I might get more useful information to describe it?

Thanks
 

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Discussion Starter #4
Thanks, Cougarr and Greenbird. I don't feel any vibration at all when the rattling occurs. I'll check out the heatshield.... any more ideas?
 

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Yup

I agree with the heatshield thing...I had a noise that was a vibration...sort of like vibrating metal..didn't bother me much, it only happened when i was going up hill on a turn fast...* months later, i find out it was a heat shield...just welded it and no more noise.

BeirutsFinest
 

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VERY important question:

You say you hear it at WOT. This means that when you hit Wide Open Throttle, you're hearing this "rattling" noise. Does it occur at all RPMs or just a particular RPM range?

The reason I ask is simple. If you don't know what you're hearing is detonation, you could easily attribute it to something else. One way to know is when you hear it, back off the gas slightly. If it goes away, it probably is detonation (or "pinging"). If it's indeed a vibration induced rattle, it'll still happen as the RPMs climb. However, if you're pinging, you need to find out why and fix it. Detonation will hurt your motor eventually. Period.
 

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Discussion Starter #7
Thanks, good point. The rattling seems to occur only at WOT, say around 4k RPM or so. That's the only time that my RPM's get over about 3k. I'll try running it at high RPM's but not WOT, and see if the rattling continues. I'll also try running some higher-octane gas on my next tank and see if the rattling stops.

This problem first began occurring about 6 months or a year ago. That was the same time that I started getting "check engine light" warnings about running lean. Do running lean and detonation frequently occur together?
 

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Yamyam said:
Do running lean and detonation frequently occur together?
ABSOLUTELY! Running lean is the number one cause of detonation. Second would be too much spark advance, but that's not gonna be your problem. The only other potential cause would be a hot spot in your cylinder, but I'm guessing it's just running lean.

Increase your octane, replace your fuel filter if it's got more than 15,000 miles on it, and or get your injectors cleaned.
 

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Sir William said:
Increase your octane, replace your fuel filter if it's got more than 15,000 miles on it, and or get your injectors cleaned.
and I doubt he means "injector cleaner" in a bottle. I think my mechanic charged me $30 to clean all 6 injectors on my 89. I figured it couldn't hurt since they were 10 years old.
 

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Discussion Starter #10 (Edited)
Yikes.... it's gotta be detonation.

I've just dug out my maintenance records... here's the complete background: I've got about 36k miles on the car right now. I got my first "check engine" due to running lean at 33k miles in May02, and fixed it by replacing the fuel filter (did it myself, hurrah!). I got another "check engine" from running lean a few months later, and fixed it by adding a bottle of injector cleaner and avoiding the cheapo gas stations since then. I've just gotten my third "check engine" warning, also for running lean. I can't say for certain when I first noticed the rattling noise, but I think it was at about the same time that I got the first running-lean warning.


Any idea why my low-mileage, nearly-stock '97 bird is running lean with detonation? Is there anything I should be doing to keep the injectors clean? I normally use 87 octane gas from any name-brand station (but I'll be using higher octane until this is resolved).

Thanks for all the info, I think you've just saved me from some major problems down the road :) Could you point me towards some info on why running lean causes detonation? It seems kinda counterintuitive to me.
 
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