PCM Reflash and/or Timing Change

[MJEasly]

I just got my truck back from the shop and have noticed a change in pitch of the turbo. Before it was a slight whine whereas now it has a more pronounced, deeper whine, almost like the impeller is grinding or is rubbing the housing ever so slightly. Visual inspection turned up nothing unusual. The service included a PCM reflash and a timing adjustment. Granted, I am typically sensitive to all of the noises the truck makes when I get it back from service, but in this case I think something is definately different.

My question: Can a PCM reflash and/or timing change cause the pitch of the turbo to change? I am guessing that if the new code has a different boost map, then perhaps yes. Any thoughts?

I'll go ahead and pull the intake off of the turbo and see if there is anything causing the pitch change.

Thanks

[MJEasly]

I don't buy the new code causing the turbo to sound differently argument. The best way I can describe the noise is a high pitched buzz/squeal that comes on with boost. It will stay on and then abruptly shut off. It may not even be related to the turbo, but can only duplicate the noise when I roll on the boost.

Vacuum lines are in good condition. Vacuum at the turbo 10-15 at idle.

The wastegate moves freely.

The impeller in the turbo spins freely.

Anybody have any ideas?

99 K2500 w/6000

Thanks

[GMCfourX4]

Do you have gauges installed? Are you getting the same boost pressure? I can't think of anything that would cause the noise you're talking about except maybe if there was a leak under boost, and the noise was due to a seal/gasket/something that was vibrating as the air pressure blew over it... Is there anything you can say to describe what's happening?

-Chris

[MJEasly]

Chris,

The only additional information I can think of is the intake manifold was off to replace the FSD. They reflashed the PCM and reset the timing. Everything seems to be in place. The problem is that I can only duplicate the noise when I apply 3/4 or more pedal under load - no luck hearing it when the hood is up.

I don't have boost or pyro, the truck is mostly stock.

I am really stumped on what this could be. My gut says that the noise is related is related to the turbo, but I don't want to limit the scope of investigation to circumstantial observations.

I'll check again for any loose bolts/gaskets or other items. Would a leaking head gasket make these noises? Any ideas would be greatly appreciated.

Thanks,

Mark

[ 10-09-2003, 05:47 PM: Message edited by: MJEasly ]

[GMCfourX4]

Mark;
The only thing I can think of (kinda grasping at straws here) is that maybe the silicone hose connecting the turbo to the upper intake isn't tight, and under boost the pressurized air leaking out is causing it to vibrate? Check the 2 spring clamps to amke sure they're tight, and see if there are any signs of air/oil leaking out around the hose. If that's not it.... I'm stumpted.

-Chris

[MJEasly]

Chris,

That makes a lot of sense to me since they had the manifold off. I'll check it out.

Mark

Update:
-Turbo hose is tight and clamps seem secure
-Noise only appears at 2000 rpms or above
-Can not reproduce the sound unless driving

How about a manifold leak? How would I go about testing that? CDR? Anything else I can isolate and test?

Thanks,

Mark

[ 10-10-2003, 06:34 AM: Message edited by: MJEasly ]