Engine noise on deceleration

[PCR]

My truck has made an alarming noise several times now and I'm wondering if anyone else experiences this. It happens only under load when climbing mountain passes (I live in Colorado). I've heard it when coming off the throttle quickly at moderate speeds (2nd or 3rd gear) and recently during the shift from 3rd to 4th when accelerating after being slowed down by traffic. When I'm going between 50-60 mph with O/D off on a steep grade I can accelerate and quickly come off the gas and get the noise to occur almost every time. If I come off the throttle slowly, there's no noise. The noise is difficult to describe, sort of a rapid popping. It definitely comes from the passenger side of the engine compartment. I brought it into the dealer and they said it's caused by the air filter and air box when there is a quick change in how much air the turbo is pulling. They quoted some service bulletin and said it's normal. I guess this description sounds reasonable, but the noise sounds more mechanical than just a vibration in the air filter. Wondering if anyone else experiences this and if it's anything to be concerned about? Thanks

 

[HOBrian]

If I am wrong someone chime in. If you are pulling a load and need to take your foot off the go pedal fast the turbo needs to get rid of all that extra boost it made. That event is what you are hearing. Waste gate opening fast and letting the air out.

 

[Rineholio]

Mine does it too, and it was especially noticable after I installed a free flow muffler and an AFE filter. I was thinking wastegate also. It's been going on as long as I can remember, so if it was going to go, I figure it would have gone.

 

[rbattelle]

It's called turbo bark, and it is not nice to do this to your turbo. Basically, you've got loads of pressure in the manifold and a sudden drop in exhaust energy. The compressor no longer has enough energy to continue compression, and flow actually reverses through the manifold and intercooler, stalls the compressor, and in severe bark actually stops the compressor. This is very bad, and can result in a broken turbo shaft.



Simple solution is to be more "gentle" with your throttle movements.

 

[Jengle]

What rbattelle said. Barking the turbo will break it, just a matter of time. Roll off the throttle, instead of lifting fast.

 

[Rineholio]

Mine does it at moderate throttle just locking up in overdrive at about 50 mph with no change in pedal pressure. What's up with that? It's a grinding noise that is definitely coming from the turbo area. Is it time for a new and improved turbo, i. e. one that would be better suited for more fuel?!



By the way, is this common with all turbo diesels?

 

[PCR]

Thanks for the information. Is there potentially something wrong with my turbo if this happens frequently? I'm definitely not driving the truck aggressively when this happens. Mountain driving in Colorado is fairly harsh anyway you look at it, but that's part of the reason I bought a diesel. I'd think this truck should be able to handle any of these mountain passes when unloaded without potential damage. It should be able to easily handle twice the load I'm subjecting it to. I don't know what I can do to be more gentle when the auto transmission shifts from 3rd to overdrive when going uphill.

 

[PGiannetto]

and i thought i was the only one. mine does the same exact thing when mountain driving. how do you go easy?? i am on a winding narrow mountain road, pressing on the pedal & releasing on the curves. that is when it happens. i am not going more than 35 mph most of the time. so how do you go easy on it? i thought i already was.

 

[CLAYTON]

Mine used to do it but doesn't any more after installing a new intake and exhaust.

Originally posted by Rineholio

Mine does it at moderate throttle just locking up in overdrive at about 50 mph with no change in pedal pressure. What's up with that? It's a grinding noise that is definitely coming from the turbo area. Is it time for a new and improved turbo, i. e. one that would be better suited for more fuel?!



By the way, is this common with all turbo diesels?

The reason that you get the "bark" when shifting into OD is because of the difference in psi from 3rd to 4th gear. . the shift causes a sudden drop in psi and causes the bark. You don't even have to have your foot into it to notice. If this is wrong somebody correct me.

 

[Rineholio]

I just reread the original post, and mine doesn't pop. It just sort of sounds like a grind, like something spinning is rubbing on something. Pretty scary, eh? It's done this since new, but only rarely when you lifted off suddenly after pulling hard. That was with the stock muffler. Now that I have a Hog, I hear it a lot more. Letting up more slowly has eliminated the sound. The first time I heard it, I thought it was the transmission.

 

[sag2]

Just drive it. They all do it, and if it breaks (highly unlikely) in the first 100,000 miles it gets fixed for free.

 

[Vaughn MacKenzie]

It's not the sudden drop in PSI during an upshift that causes the huffing, but it's the drop in engine RPM. The engine is flowing say 700 cfm as you have your foot on it in 3rd Gear then when it shifts the RPM drops immediately and you're only flowing maybe 500 cfm due to engine speed and suddenly there's not enough exhaust drive air to keep the air compressed on the intake side. So it huffs and barks.



I don't think mild huffing when the truck shifts during acceleration could be that bad for the turbo, it's not as hard on it as going full throttle then suddently letting off the throttle completely.



Vaughn

 

[Rineholio]

I've been ignoring it for 12,000 miles, half of that towing 11,000lbs. I feel even better now! Thanks for the responses, everyone.

 

[CLAYTON]

Originally posted by Vaughn MacKenzie

It's not the sudden drop in PSI during an upshift that causes the huffing, but it's the drop in engine RPM. The engine is flowing say 700 cfm as you have your foot on it in 3rd Gear then when it shifts the RPM drops immediately and you're only flowing maybe 500 cfm due to engine speed and suddenly there's not enough exhaust drive air to keep the air compressed on the intake side. So it huffs and barks.



I don't think mild huffing when the truck shifts during acceleration could be that bad for the turbo, it's not as hard on it as going full throttle then suddently letting off the throttle completely.



Vaughn

Yeah. . what he said

 

[nickleinonen]

Originally posted by Jengle

What rbattelle said. Barking the turbo will break it, just a matter of time. Roll off the throttle, instead of lifting fast.

or get a blow off valve installed. either BD's turbo guard setup, or something home brew



i have an idea for one, which will cost ±$50 plus the cost of a used/new ricer BOV. not real high tech, but should work [5psi hobbs switch, GM 6. 5TD wastegate vacuum solonoid (or some other vacuum solonoid) BOV, surplus egr electric vacuum pump, microswitch, misc. wiring/tubing]

 

[rbattelle]

This problem seems to be more pronounced with automatic trucks, and more so with the "600" engine. I believe this is due to the "600" running considerably more boost than the 2003 engine (32 psi max vs. 23 psi max).



I don't really see how a blowoff would work... don't they just vent to atmosphere at a preset maximum boost value?

 

[GWoody]

First time I noticed it I was pulling about 12000 in 4th gear, pedal to the metal pulling a grade, going about 50 boost was about 37 and young girl on a cell phone pulls out in front of me I had to get off the throttle and get on the brake, I heard a whoof, whoof, whoof very rapid, never saw the dog but I'm sure this was what everyone refers to as turbo bark.

 

[Prairie Dog]

It's a lot worse with a fueling box.

I thought I read someplace that the TAG stops the bark, anybody have this experience?

 

[AHutchison]

The way the blow off valve works is when you let off the pedal fast, all the air is going in reverse towards the turbo. The blow off valve lets all the air out of the hose atmospherically. This prevents the turbo from trying to spin in reverse and possibly breaking the turbo shaft. These high HP diesel engines and high HP rice burner engines all have blow off valves on them. This will save your turbo.

 

[PGiannetto]

good info, thanks! i just can't see how this could be normal. how can you explain or show this to the dealer? it never happens to me on flat ground, only in the mountains. the mountains are 45 minutes away from the dealer.