when I hold my engine at a steady rpm. liek 2k say. the exhuast basically"turns on and off" it like someone put a rag over then,takes it off. Doesnt only do it at a steady rpm. if i rev it up, on the rev down its like tone/ pause/ tone /pause then right when it idles down all the way it has a steady tone. If i pull off the air pump hose that goes on the front of the air cleaner it pulses too. it sounds so goofy and annoying. My valve on the exhuast air tube is good. the little air valve on the end of the air cleaner housing isnt doing it. is this normal or is somthing not working?

 

I'd do a valve adjustment, see if that helps any

 

no... the valves are adjusted. the motor istelf runs perfect and steady. just some smog device or somthing makes it pulse.

 

If your truck is California smog, then it most likely has an EACV. The EACV turns on and off to allow air into the exhaust for the catalytic converter to work properly. It will pulse and can be loud if the resonator is broken. It is suppose to turn off and on. Check that the resonator (the black round canister looking thing under the air cleaner) is not broken. On my 2wd, the bottom of the resonator is melted off and it is noticable when it is on. I am not familiar with the federal smog system, but I would think that it has a similar system for controlling air into the exhaust.

 

its a ca truck. Im pretty sure that canister is fine. I took it off when i rebuilt my engine and it seemed fine. I guess i need to live with it, its just annoying listening to my exhaust turn on and off.

 

That canister is basically just a muffler. You could always try getting another one from a junkyard. I am not sure if there is anything inside of them to wear out or not.

 

Did you ever figure out what was going on with this? I have EXACTLY the same problem on my '87 Cali pickup.

 

Did you ever figure out what was going on with this? I have EXACTLY the same problem on my '87 Cali pickup.

 

The system that would make that noise is the system that allows air into the exhaust for smog reasons. Underneath the intake manifold is an electronic device (EACV) that is attached by a rubber hose to a round black canister (resonator), which is then attached to the air cleaner housing. The EACV turns on and off, and the resonator muffles the exhaust noise. There could be a crack in the resonator, the rubber hose, or possibly a leak in the valve itself. I would think that if there was a problem between the valve and the exhaust system, then the noise would be constant and not turn on and off.