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Engine Question('98 3.3 L)


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Hey,

 

I noticed that around 1000 RPM I have some sort of rattle from the motor. It is just around 1000, and it immediately goes away at engine speeds faster and slower. Not sure if this is valve flutter/lifter etc? Has anybody else had this? I just got my timing belt replaced, if that helps.

 

I had an old mazda truck and a subaru that seemed to have the same type thing, and as annoying as it was, it never seemed to effect anything.

 

Any thoughts?

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Exhaust heat shielding. Could be something else, but many have been tricked by the sounds of the r50 exhaust rattles.

 

I think valve train noise sticks around thru the rpm range. Harmonic vibration is more likely and the first thing to vibrate is going to be the exhaust heat shielding.

 

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Edited by onespiritbrain
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A video demonstrating the sound could be helpful, but I agree with the heat shield thought. How much of the exhaust was replaced? There might be portions close to the engine left that have original shielding.

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I thoroughly agree, it's most likely a heat shield loose, they're notorious for that. Check the shields above the cats, they usually start first, you cure one and another starts soon after...

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Mine makes a similar noise right around 1000 rpm as well, sort of a rasping/rattling sound. It isn't coming from any heat shields or any loose parts, it's coming from the exhaust itself. Like nowhere on the pipes is it making the noise, you can only hear it coming out of the end of the tailpipe with the rest of my exhaust noise. I never heard this with the stock exhaust (which I cut off right after the muffler), but it appears to be present both when I had no exhaust besides the foot or so directly after the cats, and also with my new exhaust, which dumps all the way out the back. Not sure my problem is related at all, but I've been dying to figure out why it does this. It sounds awful and no matter what I do it won't go away.

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My 98 Pathy has a rattle up to about 1600 ram's and goes away. It's my valves no doubt about it. I use 87 octane majority of the time but on occasions I will use 93. When I use 93 little to no rattles at all. Hope this helps.

 

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My 98 Pathy has a rattle up to about 1600 ram's and goes away. It's my valves no doubt about it. I use 87 octane majority of the time but on occasions I will use 93. When I use 93 little to no rattles at all. Hope this helps.

 

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If it goes away with higher octane, then that would be spark knock, not valves. If your vehicle runs fine on lower octane, then running higher is a waste. That is not the case here. This is a situation where higher octane is warranted.

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Thanks for the lesson. I'm a shade tree mechanic with little knowledge not so much about spark knock. Have no clue what your talking about. All I know is my Pathy runs better with a higher octane. I know what a valve rattling sounds like and that's exactly what mine does between 1000 to 2000 RPMs. Not so much with a higher octane. Call me crazy but I know my R50 better than you do. Not trying to sound like a smart ass. I will look into the spark knock thingy your talking about. This is why I love this forum

 

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Edited by Mrelcocko
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If it were valve noise you would hear it at idle too. Spark knock/preignition/predetonation are all the same thing. It is the fuel igniting before it is supposed to. It causes a ticking/pinging noise under acceleration. Many people mistake it for valve rattle. That is why it goes away with higher octane fuel, the higher the octane, the harder it is to ignite. So it doesn't ignite before it is supposed to. Many things can cause spark knock. Too low of an octane fuel, timing advancing too much, too hot of spark plugs, etc.

 

If it were truly valve noise it wouldn't change with octane, as valve noise is mechanical and changing octane would have no bearing on it.

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If the valves were loose, I'd expect the motor to burn a ton of oil. Also, like Citron said, loose valves wouldn't change their behavior with higher octane gas. The only thing octane rating should change is preignition. Having it only happen at low revs makes me think you might have a vacuum leak that's leaning out the mixture.

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If it were valve noise you would hear it at idle too. Spark knock/preignition/predetonation are all the same thing. It is the fuel igniting before it is supposed to. It causes a ticking/pinging noise under acceleration. Many people mistake it for valve rattle. That is why it goes away with higher octane fuel, the higher the octane, the harder it is to ignite. So it doesn't ignite before it is supposed to. Many things can cause spark knock. Too low of an octane fuel, timing advancing too much, too hot of spark plugs, etc.

 

If it were truly valve noise it wouldn't change with octane, as valve noise is mechanical and changing octane would have no bearing on it.

I see where your coming from now. Thanks for the clarification. Makes since.

 

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