Possible Turbo Problem???

[Bobalamm]

Something new has been occuring while driving on the freeway. When I am at steady speed and accelerator pressure (cruise control would be a good example), I can hear the turbo revving up and down or cycling up and down. The engine RPM's remain constant. There is no lag in power upon acceleration. Two follow up questions if it turns out to be a turbo issue: 1) Replace now or let it fail? 2) How easy is it to remove/replace the turbo if this indeed sounds like a turbo problem? Thanks for the help.

[DmaxMaverick]

Any problems, other than the sound? Less power? Missing? Smoking? Any other sounds? SES light on? What year, engine model? Mod's?

FYI....
The turbo "noise" is not controlled, entirely, by APP input, speed, load, or RPM. The turbo boost is not controlled, entirely, by APP input, speed, load, or RPM. All of the above, among other things, can and do make the turbo "sound" and perform different. Compressor output (boost) and sound will vary, depending on fueling, APP input (throttle), load, air density/temperature, and fuel quality/flow.

Most likely, you are just now noticing a noise that was there before, or your intake plumbing may be loose at some point (Diesel intakes can be very noisy, if the plumbing is not completely intact). What you describe does not sound like a failing turbo, or turbo component. A noisy turbo is a happy turbo. Any component failure will cause noticeable symptoms, and "normal" spooling/despooling sounds isn't one of them. If you have an LLY or later, there are issues with the vane positioning servo, but there will also be accompanying DTC's, as well as several other symptoms.

[Bobalamm]

Sorry for that lack of details. 2003 LB7. The only "mod" is the high idle hooked into the cruise control (directions from this site). No loss of power, not missing, no smoke. The SES light was on last week so I took it to the dealer, they replaced injectors (3rd time) and the EGR tube. The noise was definately there before the SES light came on. I was expecting the noise to go away after they performed the work. The "noise" is definately the "normal" spooling/despooling noise, it's just occuring without accelerator input. I am presuming that somewhere in the FYI portion of your post, accelerator input was discussed. I am a rookie it comes to advanced engine talk. Thanks for the quick reply.

[Mark Rinker]

I would verify that that boost feedback (~3/8" black rubber tube) that runs from the intake to the turbo wastegate wasn't disconnected or cut during the recent injector replacement.

If it were unhooked, the turbo could be overboosting, and surging. Was there an overboost code set when the SES light was illuminated?

[Duramaster]

Or how about............. do you have any holes drilled in the firewall for aftermarket wiring of any kind that would allow excess noise into the cab? Are you sure it is a turbo noise and not refrigerant flowing through the AC evaporator? Something to think about. :)

[Bobalamm]

OK. Update. Maybe someone can explain this. I was in a drive thru and I could tell the engine was "cycling" or surging. I get the whirring of the turbo spooling/de-spooling at highway speeds and the engine surging at idle (In gear). That seems to tell me it is an engine issue that translates to the spooling/de-spooling noise at speed??? At idle (In gear), the tach doesn't show any movement but it sounds as though it would be a 100-200 RPM surge up then back to normal idle RPM, never below. When it surges, there is no forward movement and I do not need to apply extra brake pressure to keep the truck from moving. When I put the vehicle in Park, it idles normally. I don't know how concerned to be since there does not seem to be a performance issue. Thanks again

[DmaxMaverick]

Sounds like unstable fuel delivery. Could be a number of things. How old is the fuel filter? Could be an air leak (fuel filter related), fuel restriction, or fuel pressure regulation. Being so soon after an injector change, I'd suspect the fuel pressure regulator if there's no air leak. You'll have to look at real time fuel pressures, commanded versus actual, and the stability at given inputs. You'll need a Predator Programmer or full function scanner to read these values.

And, just for shoots and grins, keep an eye on your engine oil level.

[Bobalamm]

Wow, it sounds as though it is back to the dealer. Man I hate that. I have yet to find a mechanic that will work on the diesel. Thanks

[Mark Rinker]

FWIW after finding out the cost of replacing the FPR on my 2002 K2500, I proceeded to put on about 75K miles with a slight surge at idle.

For over $800, I got used to it. :rolleyes:

Just one other thought - the first Predator tune that I ran on that truck had a noticeable surge when at cruise speeds. Idle was normal. Are you running any performance tune?

[Bobalamm]

No performance mods. I tapped into the ECM to do the high idle mod. I don't use it much anymore so I may remove that. If it isn't doing damage I am inclined to leave it alone, especially for $800.

[DmaxMaverick]

No damage, if it's only surging, slightly. If you can't see it on the tach, no damage for sure. GM's spec is a 100 RPM swing, before they'll warranty a repair. Your high idle mod isn't part of this, so I suggest leaving it.

[Bobalamm]

Thanks for the details. I will hold off and cruise right along.