Diagnose this sound
I've got a weird sound I need diagnosed if anyone has any insight.
The sound is like a hissing, sorta' what a closed EBPV sounds like through the exhaust and inside the cab. The sound I'm hearing is not very loud but enough to hear in the cab and a little outside the cab. Just noticed it recently. Sound doesn't get louder or quieter with different RPMs, constant with light throttle/no throttle. The sound does not effect how the engine runs, it's just another sound.
The sounds seems to be dependent on two things, either the gears I'm in or RPMs/Load. When in overdrive when the RPMs drop I can barely hear it - if at all, and once the turbo spools you can't hear it.. drive the PSD up to 35-40 without overdrive on, lift your foot off the go pedal and it sounds like the EBPV is closed. Seems to be coming from the firewall area, not too sure. Also, if I'm in motion and throw her in neutral the sound goes away or gets to where I can't hear it.
I've looked through the exhaust, no black soot leaking past - nothing on the firewall. Downpipe clamp is tight.
I even put compressed air up to about 5PSI (reading from the boost gauge incab) through the whole CAC system and could not duplicate the sound. I re-torqued every CAC boot clamp just to be sure, checked the plenums clamps. I checked the compressor wheel on the turbo, no play. Air filter is new.
I've unplugged the EBPV, went around the street, still there. Could the flap still mechanically be sticking somewhat shut? I unplugged the wastegate hose, still there.
The truck itself does not shift, or act different. Power is still there. At idle, can't hear anything. In short, there is nothing physically from my sense of feel different except for this sound.
Change gears from Park, to Neutral, to Drive, or Reverse to Neutral - whatever, you can hear a faint sound before it actually goes in the specified gear that reminds me of the constant sound I described.
Anyone have any ideas? I'm stumped. I thought about driving down the street without the accessory belt on. How do you check if the wastegate is stuck open? I assumed taking off the red hose would figure that issue out.
Maybe it's normal and I'm paranoid but I swear I never heard it before! Could a pulley make this sound? Specifically my mind keeps telling me to look at the AC compressor, I've had the AC on through this whole time for the most part.
Thanks, sorry for the long post, everything should be crystal clear though.
Last edited by Lord Tauk; 08-26-2007 at 01:19 PM.