Turbo spools on and off at idle

2003 Detroit 60, 12.7 L, DDEC 4, EGR.

While idling, turbo will cut in and out, spooling up and down. Sometimes it happens while climbing a gradual (not steep) hill. I can hear it start to whistle, then cut out and truck has a deep, throaty sound. The idle doesn't change.

Anyone have an idea what it could be?

 

Have you opened hood and stood by the turbo with the engine running? Turbos I know of can't spool up or increase revolution without more exhaust air. Mayby you have loose exhaust clamp, or even loosely mounted turbo. Had one work loose that had only been on a week or so. Mechanic didn't torque it properly. It was moving around some and sounded way different than normal. Move things around turbo, air-air pipes, hoses, even pull and push on turbo. That's my amateur assessment .

 

Sounds like normal, to me if engine is cold. It has a warm up mode.

 

Didn't think about these new fangled engines and the "warm up mode". But he did say also on a gradual pull.

 

Are you sure its a 12.7L? I wasn't aware they produced the 12.7L as an EGR engine. I was under the impression all EGR Series 60's were 14L

If it is an EGR engine they tend to do that when EGR is active IIRC. The burnt exhaust gasses bog down the engine (more or less loading up the engine due to lack of oxygen) so the turbo spools up slightly as the engine is working to maintain desired RPM.

 

It does it when engine is cold and hot.

 

Mine has the variable vanes setup. Maybe more exhaust is not required

 

You have a exhaust temp guage? If so on the gradual pull is it the same? Are you owner op? Now we wonder..is it a 5.00 noise..or a 5,000 dollar noise.

 

Yes, 12.7 L with an EGR. Had the truck since 2005

 

No exhaust temp or turbo boost gauges