I have 2001 Blazer 4.3L (auto tranny)with 137,000 miles that just started making a weird noise. It is making a rattling noise or lugging noise when accelerating betw. 1,000 to 2,000 RPMs (soft acceleration only). Seems to be most noticeable in 2nd gear? Can really tell what it is. Not sure if it is detonation. Almost sounds like bottom end noise? Blazer does have a little rough idle.

Noise started after replacing water pump and hoses.

Can only hear this noise when driving. Can't duplicate noise while parked with engine running.

Plugs (ac delco rapid fire), wires, cap and rotor, fuel filter have been replaced recently.

No codes? Any ideas?

 

Bad universal joints maybe?

 

If the noise wasn't present before the water pump change, I would suspect a problem with one of the components removed/replaced/reinstalled during the installation.

Another thing that comes to mind is a TSB on the balance shaft which details a rattle type condition between 1800RPM & 2200RPM --> CLICK HERE for further information.

 

Thanks for the link to that thread. The only connectors unplugged were to the MAP, EGR valve, ICM and alternator.

Could the coolant temp. sensor be acting up and causing this? I did do a Prestone flush prior to installing new pump.

Thinking of taking off throttle body and cleaning it. May also clean the IAC and TPS with some MAF sensor cleaner.