I have a 99 F350 with a 7.3L Power Stroke turbo diesel. when I accelerate to a steady RPM I hear a hissing sound like air is being released. At the same time the engine seems to lose power and the rpm's drop. This happens anytime i hold a steady rpm weather driving or in park. If I accelerate it stops until the RPM's hold steady again. Also, on an immediate cold start it doesnt seem to do it. After 30 seconds or so, as the engine warms up the problem appears. Does anyone know whats wrong? Any feedback is greatly appreciated.

 

sounds like a boost leak. you have air leaking out around boot or something in the system

 

It is your Exhaust Back Pressure valve. It closes when the truck is cold. Normal operation when the oil temp is below a set point. Let the truck warm up more before driving it and you should not see it when driving.

If its still doing it when on the road and warm then the EBP sensor is most likely plugged. Clean the tube and or replace the sensor.

 

Welcome to FTE.

Here is how to clean the exhaust tube and sensor. click here. It does sound like the EBPV is closing. I have the decel on my tuner and thats what it sounds like when the valve closes.

 

I had a buddy under the truck to listen and he said it sounded like the air was dumping into the exhaust when it was making the noise.

 

When you try to drive it does it pour out black smoke from the tail pipe? Look in this part of the turbo this is where this warm up valve sits

 

no it doesnt have any black smoke. The exhaust seems very normal.

 

Look at the blue hose in this picture then check all large pipes coming out of turbo into the air cooler and out.There could be a hose clamp loose or off.

 

I will check it out, thanks. It feels like a valve or sensor operating incorrectly. Could this problem be anything other than the mentioned ebp valve considering the symptoms? Thanks for the help everyone.

 

If it was a sensor I would think you have a check engine lite! Just to be safe get your truck scanned and check for codes. Im not sure about your mechanic ability but yes the exhaust warm up valve can stick shut and cause problems like low power.

 

Your right, there is no engine light, no pending or prior codes and all the monitors are running. Some vehicles dont throw codes right away. It could take extended driving to get a cel to come on.

 

Could be you are listening to the turbo whine at the air cleaner and exhaust? Need more info here if you checked all this out if no smoke is present or no codes.

 

Is there any exhaust leaks?

 

I have been having the same problem. When I am at a constant speed on the freeway the boost pressure goes way down to like 1psi but when the engine gets up to temp it goes away. It has more of the hissing sound while in town when the engine is at lower RPM but only while at constant throttle. It goes away when I am completely off throttle or when I accelerate. It was a big problem up untill last week when it got up to 50+ outside and then it did not happen. It is probably the EBP sensor and I will be cleaning it out in the next weekend or 2.

 

That's more than likely the EBPV doing its job. Once the truck is warm, it quits doing it, right? Completely normal operation in the winter...