Metal Rattle Sounds When Excelerating?

[yenz]

hi i have recently purchased a 99 3.8l mustang from a car lot it was a trade in any ways i have a problem when i put my foot on the gas and get on it
i hear a metal rattling sound comming from the engine i do not no what it is it doesnt seem to do it when i have the car parked and have the hood up and idle the gas to a high rpm my car was olso backfiring pulling out from a stoping point i took out my spark plugs and changed them with some double plats and that fixed the problem with the backfiring i took the old plugs to a mechanic and he told me my car is running to rich and the metal pinging sound is still there after i changed the plugs olso i have another problem when i excelerate at a high speed say 100 and slow down to 70 i will be in 5th gear and my car car will Hesitate sort of a bog and then go away and it only does it when i go at a high speed and slow down it's wierd to explain now if i go at a high speed then slow down to the point where i can downshift to 4th it doesnt do it i olso no there is a speed limiter on the these cars maybe it's something with that i have no clue i will get that taken off soon

 

[98CobraClone]

valve lash?

 

[Skymarshal]

The first thing you need to do is to go down to the punctuation store and buy a bottle of periods. Use them liberally. Please!

It sounds like some sort of problem involving the mixture. Do you have a Check Engine light? Is the fuel filter original? Have you tried running a bottle of fuel system cleaner through?

 

[gkrawchuk]

when you have the hood up and bull on the throttle cable can you hear the metal rattling? you might have an exhaust leak. Check your manifold for a crack or even if it is broken. you might just need a new gasket or a new manifold. If that is the problem just strap on some headers, they are easier to install and caost a only a little more.

 

[976er]

What brand of fuel are you running? I have found that chevron with techron works best because it burns cleaner than cheaper fuels, you will also get better gas mileage.

 

[03v6]

... if i had to guess

1)ECU
2)Fuel System

skip all these...




15)Exhaust lead- but it still could be...