Rattle from under hood when under load??

[LEOMAC23]

Hey I have a 97 3.8 firebird and when the car is accelerating under load it makes a weird rattleing noise, almost like spinning a marble around in a tin can so at first i thought it was detonation but after using premium gas for a while it seems like its getting worse, I also have some lifter noise and was wondering if this is causing it. Does anyone no what this noise is cause its drivin me nuts and i want everything fixed before storage time. what else can cause detonation? could it be a bearing somewhere cause it sorta sounds like a worn bearing. any help would be great!!

[Bonemaro]

Re: Rattle from under hood when under load??

You know. The marble in a can description is exactly what my tranny sounds like right now. Do you have a manual or auto?

[Finkledbody]

Re: Rattle from under hood when under load??

Wow... I thought that noise was my underdrive pully

Definitly coming from my engine bay... Not trying to thread jack just showing your not the only one :tup:

[LEOMAC23]

Re: Rattle from under hood when under load??

mines an automatic,whats yours?

[cam98aro]

Re: Rattle from under hood when under load??

its valvetrain noise

im betting it is the same noise as when you are in teh wrong gear and trying to floor your car (with a manual anyways)

[Bonemaro]

Re: Rattle from under hood when under load??

mines an automatic,whats yours?

Manual... mines the T.O. bearing... Clutch chatter FTL.

[ssms5411]

Re: Rattle from under hood when under load??

Check your heat sheilds by the CAT and also check the CAT it might be coming apart.

[OneEightSeven]

Re: Rattle from under hood when under load??

A bad cat would be a possibility depending on exactly where the sound is heard. Does it sound more like the bottom of the car? About a year ago my OEM catalytic converter went out (wafer or w/e broke up and was bouncing around inside it) sounded exactly like someone kicking a can around.

[LEOMAC23]

Re: Rattle from under hood when under load??

It sounds more like its coming from under the hood and its only when i accelerate somwhat hard it rattles like if u were banging a screwdriver inside a tin can, it goes away after the car reaches speed.but if you hit the gas again it will do it again

[Rob Bell]

Re: Rattle from under hood when under load??

That does sound like spark knock. You could try octane booster to get the octane up to a ridiculous level to see if the pinging goes away. Maybe there is carbon buildup in the cylinders or the engine is running hotter for some reason? Maybe for some reason the timing may be a little too advanced. I think the PCM advances timing when cold and retards it a little based in engine temp. If this is the case (research required) then a faulty temp sensor could cause advanced timing and therefore pinging. Same deal with the IAT sensor. If it thinks the air is cold when it's really hot outside, timing may not be retarded enough.

[LEOMAC23]

Re: Rattle from under hood when under load??

well i already tried octane boost in it with high octane gas and it did nothin. Tho it is raining here and it seems better when its wet for some reason , could there be a bad spark connection that the water is fixing??or what else would or could the water be helping to rid this problem? thanks for the responses

[Rob Bell]

Re: Rattle from under hood when under load??

Interesting that rainy weather causes it to go away. Rainy weather sometimes has an effect on ignition components. Have you checked to make sure your plugs, wires and coils are all in peak condition? Also, rainy weather is usually a little cooler, maybe that is helping the detonation by giving you cooler, moist intake air. I would try testing those temp sensors just to make sure they are sending accurate readings to the PCM.