Knock when accelerating, especially up hills.

[gmssage]

My 1997 Mustang has a noticeable, but not overly loud knock when accelerating, especially when going up hills. It is not quite so loud when on a flat road.

I just changed the spark plugs, thinking that it would be due to spark knock, but I didn't change the wires. After having the plug changed, the sound still continued.

I also tried running a higher octane gas (went from 87 to 93), but that made no change.

Any help in diagnosing and fixing this would be much appreciated.

 

[xneox]

This is one of those things that's nearly impossible to diagnose thru the 'net. Could be anything from an alternator bearing to a main bearing.

How many miles?

Oil change intervals?

Spark knock & bottom-end knock sound nothing alike, so if you can't distinguish between the two maybe you have a bud that's into cars & will go for a ride w/you to help nail this one down.....?

 

[Jamez]

Mine sounded like it was knocking when one of the primary tubes cracked.

 

[gmssage]

63,500 miles, with oil changes every 3,000 miles using Pennzoil 5W-30.

It's more of a higher pitched, extremely rapid knocking sound, and it doesn't happen at all while in park/neutral.

 

[Mach428]

Answer these questions for me, Is it one loud knock and do you have an auto?

 

[98CobraClone]

extremely rapid..........valve lash??????

 

[gmssage]

Yes, it's an automatic.

No, it's not one loud knock. It sounds like a lot of semi-quiet little knocks, rather rapid, probably about 7-10 little knocks a second while accelerating.

 

[xneox]

extremely rapid..........valve lash??????

Sounds like top-end from what he's describing.....but I've heard belt/chain tensioners & accessory bearings make that kind of noise too....

 

[Mach428]

I know on my v6, after 50,000 miles, the trans like to make all funny little knocks, every think you might be hearing something from the trans downshifting?

 

[gmssage]

If it was the transmission, wouldn't it just be while it was shifting then, instead of constant?

 

[Mach428]

allot of the v6 trans like to do funny crap, i'm not sure