Turbo Spool-down question

[Mike330R]

After a long drive when motor is good and warm (around 210) when I make a complete stop the turbo (I belive it's the turbo) makes an odd sound while spooling down.
I sounds just like a power steering pump with no fluid in it. I checked the power steering fluid and it's fine.
It also makes this noise (not as loud) when starting out (0-10mph) only when it's good and warm.

Is this normal?

Also since GM did not put a turbo temp gauge in does the computer know when it's to hot and shut it down automagically?

[Amianthus]

I don't completely understand what you're describing. Perhaps you could give some better detail.

Your turbine continues to spin for a little while after you shut down the engine (about 15 seconds). Whilst it spins down, it may whoosh, whir, or growl a bit. These are all normal behaviors.

While you're driving, the turbine spins up and down in relation to your throttle input (fuel input to the engine). If you come off the throttle too fast, the turbine can "bark". Barking is when the drive pressure is suddenly removed (you come off the throttle too fast) and the air in the compressor side is under more pressure than the compressor can hold back. So the result is that the air tries to run backwards through the compressor and you get a "woof" "woof" sound (or a growl).

The only other noise that the turbine should make is the pulse noise that you hear from the gasses (air and exhaust) impinging on the turbine blades. That's the classic whistle that you hear (and is music to my ears).

Any other variation (like a loud screeching noise, violent growling, flapping noise) are not normal.

Based on what you have given so far, I can only speculate that it's either normal, or that you may have blown the center cartridge of your turbine. Check your air cleaner assembly for restriction (or collapsed hoses, ductwork, collapsed filter, foreign material, etc.). While you have the compressor side of your turbine apart, gently grab the center shaft and wiggle it around. Measure it if you can (and have the specs.) Rotate it a little too. Check for binding of any sort and look for evidence of the compressor blading rubbing against the housing. After all of this, you should be able to determine what, if any, problems you may have with your turbine.

If you want to, give me a call or drop me an email. Let us know how you do.

[Mike330R]

Thanks for the info

I am not sure how to give better details. It may not be the turbo. All I know is after a long drive and the motor is good and hot when stopping (10-0mph) there is a strange noise. It sounds just like a power steering pump with no fluid in it. The sound it would make when you turn the wheel. It may be a growl *shrug*

It also does it when starting off (0-10mph). I want to take it to the dealer but I would have to go for a long drive 1st and teh dealer is not that far away.

[Amianthus]

If I recall correctly, the Dmax has a vacuum pump that runs the brake booster. That being the case, I was going to suggest that you have your dealer check your hydro-boost unit. But I don't think your truck has one of those units. So that's no good. Perhaps your vacuum pump needs a once over. Diagnostics from afar can be a bit tricky. I'll keep thinking about it. Anyone else have any suggestions?

[Mike330R]

Thnaks for the replies smile.gif

I will ask someone that is local to me to go for a ride.

Will also take it to the dealer.

[DmaxMaverick]

All Duramax equipped trucks have hydroboost. It will also have a vacuum pump if it has EGR. If you are having "PS pump" noises, have the dealer check the system. The PS pump supplies both the hydroboost (power brakes) and power steering. No GM Diesel equipped truck has/had vacuum assist brakes. Hard braking can cause a noise that sounds like a starving PS pump. Yours may be excessive.

You might also check out the serpentine belt, tensioner and idler, as well as all the other pulleys.

If your turbo is making the noise, get it fixed fast! It doesn't sound to me like a turbo, though. The turbo doesn't respond to engine or vehicle speed. It only responds to fuel input (load). You can be running in neutral and stomp the trottle to the governor. The turbo will will not give any response that you'll notice. If you have a straight pipe, you might hear some turbo chop, but that's only the turbine wheel breaking up the exhaust pulses. Very different than a PS pump growl. If the noise is happening at 10-0 MPH, I would suspect something related to vehicle speed, or engine speed (like a torque converter or tranny/transfer case). The turbo spools down quite quickly. If you run up to 60 MPH and back off the throttle and brake normally, the turbo is spooled down (off boost) well before you get to 10 MPH. A panic stop might beat the turbo, but I'm sure you're not doing that every time. In either case, the turbo should not be something causing any loud noises in stock configuration.

You might also check the brakes at the wheels. The rear disc has been known to "trap" debris (gravel, etc.) on top of the caliper and cause premature wear to the rotor. The rear calipers are mounted forward of the axle, and , IMO, a bad design. The problem could be a dragging brake pad, or even the "drum in hat" parking brake setup. There were some complaints early on involving the parking brakes dragging, although I've never experienced it in spite of my frequent use of it.

Outside of that, it could be just about anything. U-joints, front end diff, wheel bearings, pebbles in your hub caps, etc, etc.....

In any case, have the GM tech drive along with you while you duplicate the noise.

What year is your truck and what emmission configuration do you have (EGR/non-EGR)? What mod's have you done? This would help with diagnosis.

Good luck.

[ 03-22-2004, 09:04 PM: Message edited by: DmaxMaverick ]

[Rockin]

I hear powersteering/hydroassist pump noise. It sounds quite like when the powersteering pump went on my wife's old ford. I've had the dealer look at it twice. The first time, I had the tec ride with me after an oil change and the noise was gone. After a few weeks, it started coming back. I had them check it the next time it was in and they attributed it to vacuum. I thought it was a really odd explanation but haven't yet figure out what to do about it.

Like mentioned above, the sound changes with engine speed. It is clearly different than the turbo sound which is pretty subdued except when pulling heavy. When the noise I was hearing was louder, I couldn't identify the turbo whine except when I really got on the truck.

[Mike330R]

This noise is not the turbo whine.

I took it to the dealer today. They say it's the turbo spooling down and is normal.
It just doesn't sound right to me. I need to make sure this truck is sound before I add a lift kit. Which I found out today VOIDS the powertrain warranty after the finance guys specifically told me it would NOT. Needless to say I am not happy and will be getting a refund on the extended warranty ASAP.

Thanks for you help!

[More Power]

If this noise is easily reproduced - when the right conditions are present, you could temporarily remove the serpentine belt just long enough to eliminate all belt driven accessories as a possible cause of the odd noise. Narrowing down the possibilities is a big help.

The water pump is gear driven, so the engine won't suffer from a lack of coolant flow - airflow through the radiator - yes (no fan), but not coolant flow.

MP

[Amianthus]

Originally posted by DmaxMaverick:
All Duramax equipped trucks have hydroboost...Ya know, I thought that was the case. But I do remember getting scolded harshly by an owner, over the phone, once that he had a vacuum operated brake booster in his Dmax. And that the vacuum was supplied by the vacuum pump. Now being that I don't know everything about every Dmax ever made, I gave him the benefit of the doubt. I mean it's his truck.
Anyway, thanks for setting me straight. Now I just have to find his phone number...

[bob]

I would be willing to bet it is the whine of the allison in first gear.there is not much boost going on at 10mph and none when your slowing down.I have a video of the operation of the allison that lets you know about all of the different noises that the trans makes over a typical auto trans they really should have the sales people go over this stuff since they don't give every body a copy!!

[Rockin]

I've heard before of this video. It would be really nice if someone could digitize it and post it for all of us.

[Mike330R]

This noise happens when it is good and hot and when stopping and starting. You can actually feel it in the brake pedal.

[whatnot]

Is it only when the truck is moving?
If so, it is probably just the transmission.

[Mike330R]

Yes only when moving/stopping.

I can't see how a tranny would make that noise and also be able to feel it in the brake pedal :confused: :confused:

[bob]

can't see how you would feel the turbo through foot either!!