Engine/Transmission (1998.5 - 2002) Turbo Chuffing

[PPettit]

My turbo started chuffing today when I back off the throttle. While I understand what causes this to happen, I have never heard it on my truck before. I have made no recent changes to the truck so I am wondering what is suddenly different that would make it start doing it.

Truck is an '01 with automatic. Only hot rod stuff is an edge juice/attitude running on level 2.

Observations and things I did while looking at it today:



If I back off the throttle with even low boost I hear what sounds like an air leak. This is with as little as 1 or 2 lbs of boost on the gauge.



With a load (hill) I can still get up to 28lbs boost.



I built an adaptor to hook an air line to the rubber boot where it hooks to the stock airbox. With 10psi on the system I can hear a fair amount of air flowing thru the system. I soaped a few of the connections and found some small leaks. I pulled all the plumbing between the turbo and charge air cooler to inspect/clean things. Put it all back together and nothing has changed.



The only place I can hear air moving thru the system is up by the valve cover. Is it possible that one of the valves is partially open?



Next weekend I will throw together some more plugs to pressurize just certain parts of the plumbing but I am not seeing where small pressure leaks would cause the turbo to start chuffing.



Truck seems to run just fine but I really hate it when a new noise starts... .





Phil

 

[BILLVO]

Did you check the turbo shaft for contact or endplay when you had the pipeing off? Sounds like a turbo related issue rather than a leak. Running at 28 psi on the stock hy turbo is probably not doing it much good.

 

[GDMRTN]

Air leaks in the system will cause it to do that. The turbo has to spin faster to make the boost.

 

[Wyomingcowboy]

My turbo started chuffing today ... ... .





Phil

what is chuffing?

 

[BILLVO]

Air leaks in the system will cause it to do that. The turbo has to spin faster to make the boost.

A little better explanation.



A plugged air filter will cause the turbo to overspeed due to lack of air to compress.



Think of it like a vacuum cleaner, When you plug the hose of a vacuum cleaner it speeds up and gets louder because of a vacuum meaning it is not working as hard.

 

[JSawtelle]

?????????

what is chuffing?

Good Question? Mine makes a noise when i back off too... . just assumed it was the wastegate relieving pressure??

 

[BILLVO]

It is normally called Turbo "Bark". It is caused when you are under a load with a bit of boost and then you let off the fuel and the engine slows faster than what the turbo is trying to feed air. The turbo goes from for example 100,000 rpm to 0 rpm in a second by slowing the intake airflow that the engine will take. This is most common with auto trans versus manual because the trans will free wheel and the manual will keep the engine turning faster at coast. You could also hear it through the wastegate in lower rpm situations.

 

[JSawtelle]

Is this a bad thing to have happen???

 

[BILLVO]

Not if it only happen once in a while,but on a regular basis you could snap the turbo shaft or break a wheel.

 

[PPettit]

Thanks for the replies. I'll continue chasing any boost leaks now that I am back home.

My filter minder is not pulling down at all But I may make a trial run with no air filter installed to verify.

How much endplay should I be able to measure on the turbo? I stuck my finger inthere and spun it while I had the plumbing off but I don't have the experiance to know if it is turning too stiffly or anything like that.

I thought I remembered reading from on here somewhere that the stock turbo was good for about 30psi before the efficiency dropped off?



Phil

 

[BILLVO]

You should feel a real little up and down on the shaft and you should feel no in and out play on the turbo shaft. Check the lower aftercooler boots and clamps on both sides they have a tendency to slip off and or get cut by the fender.



BTW do not count on the accuracy of a filter minder.

 

[PPettit]

Well I finally got back to playing with this today. Pulled the rest of the plumbing off that I did not get to last week and inspected. No wear spots or obvious leaks. Put it all back together, pressurized and soaped all the fittings. No leaks that I can see.

Checked the turbo shaft and there is no endplay (in and out) that I can feel. There is a bit of sideplay. I tried to measure it with my calipers but it's pretty tough to get anything accurate. Best I can tell is about . 025" . Looks like there is no evidence of anything hitting or rubbing in there.

I guess I will drive it the next couple of weeks and try to call somebody that specializes in turbos.



Phil