Engine/Transmission (1998.5 - 2002) Woooshhh, psst, turbo bark???

[groser]

I have a strange sound that sounds like air coming back thru my air filter when I let off throttle quickly. However it only occurs at very low speeds and low throttle setting, below 20 MPH and only after I complete a pull with my trailer at highway speeds and pull off to frontage road and maybe travel a few hundred feet. If I tap throttle slightly but rapidly it makes the noise once and doesn't repeat until I start towing again at highway speeds and go thru same sequence. The noise is quite distinct and scares heck out of my wife sitting in passenger seat. We hear it loud and clear because I have a air intake hose from my air cowl near glove box to the filter box plus the stock fender well air tube. I have a AFE filter but it's just the stock looking filter that replaces the Dodge filter. The noise only lasts a second or two and has only started since I installed the following mods about 9 months ago. Quad chip; I normally set it at 70HP gain when towing, PM cold air intake, 4 " exhaust pipe, turbo back. Removed atenuator but have low back pressure muffler. It never makes the noise when I'm not towing, even if I push the truck and try to duplicate the circumstances. I didn't tow for 9 months after installing the mods so no noise in that 9 mos. Right now I'm in South Texas towing my rig trying to figure out if I've got something serious going on.

Is it possible this "air reversal" or noise was always there but with the mod to the air filter box now I hear it? I pulled the filter and it looked ok, nothing blown. The exhaust brake appears to be working normally and is locked out below 32 MPH by my controller. I understand the turbo bark syndrome since I was a jet engine tech but seems strange it could happen at such low throttle setting. I won't think the turbo could surge at such a low point. Is there anything else that could cause a noise that sounds like air rushing back thru my air filter box. ??

 

[KCanepari]

I had the short piece of hose the goes right off the turbo towards the cooler pop off and make a very loud noise like that, but I lost most of my boost. once the hose comes off you have to replace the hose and clamps. about $100, it's under a lot of pressure. use cummins hose or that high tech blue hose made for that purpose. any other auto parts hose will not work.

 

[TBartlett1]

My 98 does the same thing and is very loud at low speeds. I have twins and an open K&N air filter so the turbo whine is very audible and will (woof, woof, woof) if I release the throttle suddenly at low speeds, let me attempt to explain. When under power and creating boost the drive pressure in the exhaust drives (spins) the exhaust turbine which in turn spins the inlet compressor. As long as these conditions are stable the exhaust drive pressure maintains the energy to turn the turbine wheel creating boost. As soon as you release the throttle no fuel equals no energy from combustion heat which means no drive pressure. In an instant (under certain circumstances) the boost pressure can exceed the drive pressure. Now the airflow (boost) which was being driven into the intake reverses because the air pump (turbo) is essentially shut off. The air flow reverses and can back flow out through the air filter. I'm not a turbo expert but I would say a steady diet of this if excessive is not good for the turbo because the turbine wheels are being slowed down extremely fast which puts excessive loads on the turbine shaft bearings and seals.

The Phatt Shaft turbos are an attempt to eliminate breakage due to this phenomenon.

There is no performance advantage to the larger turbo shaft other than increased durability in extreme situations.



The most likely reason you are just noticing it after the mods is because the air box is modified, it was designed to quiet the inlet noise from the turbo, (noise pollution).

Your signature shows that you have an ATS 5 star TC as I do. This can also contribute in the following manner. When towing you can load the engine and build boost very at low engine speeds, and when the throttle is released your ATS TC slows the engine so fast that the boost air flow reverses.

The performance mods you have, air intake system, chip and very tight TC along with towing heavy combine to make it much more noticeable.





Hope this helps

Tim

 

[DCreed]

check radiator cap/ overflow bottle when you can cause this condition to see if its just a weak cap.

 

[groser]

Tim, you have relieved me greatly. Thought maybe I was going in wrong direction!!!! Your explanation was very clear, you should be a teacher!! I will learn to be a little easier on the throttle. Thx. . George