OK guys...'99 4.3...Accelerates With A 'Rattle' (knock?)

[NJGMGuy]

What do you think will cause a sound like a loose rocker arm from a mild acceleration? I'd say it was an engine knock, but don't think it would be considering such a light acceleration. It's like the old EGR valve rattles.

If it's a timing component, what might cause the timing to change and cause slight detonation? The 'rattle' is only there for a brief time and then quiets. Of course it is not there while decelerating or as engine speed and load is increased.

No Check Engine lights or temperature problems.


Thanks Guys!

[Slow_n_ez]

you might check the heat sheilds that go between the converter and muffler and the underside of the vehicle .... My 2000 Jimmy had about same sound as you describe and it ended up being the first sign of the converter going bad .........

[Jimmy58]

Hi NJGMGuy, It sounds like detonation to me. Have your timing checked. The timing can be affected by several sensors and systems. Normal everyday wear and tear will cause the timing to creap. Another aspect is that the gas you buy might have changed. I know in the North East we get a winter formula gas that is supposed to be better but I think it has less BTU's in it as my mileage goes down in the winter ( taking into consideration the longer warm up s).
My 2 cents worth, good luck
PS have your Knock sensor checked
Jimmy 58

[gmc4x4]

Hi there..i own a 2001 gmc jimmy sle 4door 4x4. i had a "rattle" coming from the engine between 1800-2200rpm's. no ses light was on. after fighting with gm they finally told me it needed a timming tensioner kit covered under a so called "silent warranty". what a huge difference it made in acceleration and gas mileage. good luck with that...

Rob, [email protected]