4.3 Harmonics Causing A Headache


#1

I have a 2001 Chevy S-10 Quad Cab with a 4.3L V6, the truck has exactly 60K miles on it and looks like it has been well taken care of its entire life, this is verified by recipts of all oil changes and maintenance and extremely good physical appearance. Recently I noticed a slight noise/vibration that I could feel in the floor boards starting at 2300 RPM and moving along until the shift at about 3000 RPM. I took the car into the dealer thin it might be a transmission issue and was told that it just needed a tune up and injection service. This I did with all GM issued parts, I also had the dealer run their little injector cleaning machine on the system. After all this was done the truck still had the same symptoms. So I took it back to the dealer. They hooked the engine and tranny up to their computer and everything checked out within specs. At this point i was told that it was just the nature of the 4.3, I told them that was BS. After realizing I was not going to take their “the computer says its fine so therefore everything is dandy” answer, they agreed to take it back and have another look. again they hooked up the computers, as well as checked the torque converter, motor mounts, driveline, and all other pertaining parts. When they still could not find the problem, they contacted the big dogs at the GM headquarters. After another day of joint trouble shooting, headquarters told the techs that it was the harmonics in the motor and that this was being caused by build up in the muffler. To my surprise the dealership told me they were going to put on a new exhaust for free. I have been tinkering around with cars for a little while but have never heard of such a thing. I am taking it in next week for the new exhaust and will keep everyone posted on the results, but has anyone ever heard of such a thing??? And why were the so eager to slap on a couple hundred dollar exhaust for free???


#2

The exhaust system is a very dynamic place from a pressure and sound standpoint. There are standing waves set up in there that move depending on the engine speed. Frankly, I don’t understand why putting an identical muffler will do. I would think that some change in shape or configuration would be necessary to make the problem go away.


#3

I had that same problem on an old car of mine when I was in college. Turned out to be the drive shaft was a little unbalanced and would cause the humming at high speed. It was not a problem but it was noisy. I put a glass pack on it and just added another noise to hide the first one.