Hi Guys,

I have a knocking noise under acceleration from idle on a 1990 S10 blazer 4.3L

The noise only appears if I accelerate moderately, under very slow acceleration it does not occur and it seems to go away if I hit the throttle hard. It also disappears when I am just cruising or decelerating.

Oil pressure is at between 50-60psi when moving while warm and 25-30 at idle when warm/hot.

At idle/stopped It does not appear at all (well something is vibrating but I do not think it is related)

The engine has 100k miles on it.

Any suggestions for a cause or somewhere to look would be appreciated.

Cheers,

Taint

 

Look to see if there are some metal specks in the oil.

 

Where does the knocking sound to be coming from? Engine compartment? Under the floorboards? Rear End?

 

the noise seems to be coming from the front end near the firewall. I can't pinpoint it though as it only occurs when the vehicle is moving. I get a bit of vibration through the floor panel from it when it occurs.

 

Tranny or tansfer case mounting bushings? Driveshaft?

 

Engine/Tranny mounts and full exhaust were replaced a few thousand km ago.

It is a RWD model so no transfer case

Edit: some additional info

RWD model
3 speed Auto with overdrive - No problem selecting or changing gears

There does not seem to be any hesitation or drop in power either when accelerating, just the knocking noise. Noise is bad so it has me a little worried as I have a road trip coming up soon.


Could it be a CV joint problem?

 

If you put the trans in drive with your foot on the brake can you make the noise happen? Doubt it's a CV joint if you are rear wheel drive - unless you have independent rear suspension. If you meant U-joint then, if a u-joint is knocking then you should be able to crawl under there and put a hand on the drive line and feel it move. I mean feel the drive line move between the output shafts of either or both the trans of rear diff. If it was me I would get a clean oil pan and drain that sucker and see if you get metal flake in the oil. Let the oil sit in the pan for awhile because the heavier stuff like metal will settle to the bottom to make it easier to see. If the oil looks good you can always put it back in the truck or replace it. But it sounds like a rod knock to me, they sometimes start out only under acceleration / load.

 

Thanks for the suggestion, got it going in to a mechanic to check it out, apartment living means no space to work on the vehicle unfortunately.

 

quick update. The exhaust was rubbing/vibrating on something under acceleration. Nice easy fix

 

I am wondering, was this vibration/knocking caused from bad motor mount(s)?