# help 7.



## dieselpusher (Nov 29, 2006)

help 7.3l 95 diesel is making a hissing noise out of the exhaust then i get on it and it goes away then comes back

its getting to be colder here if that matters


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## Vinnie (Dec 4, 2006)

Does it have a turbo ?
Is it a stock exhaust ? 
Does it go away after the truck is warm?
Does it sound like its coming from the tail pipe or a leak farther forward?
Your probly just hearing the waste gate holding back until the engine warms up . I,ve had afew 7.3 ,s and they all do that per design.


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## dieselpusher (Nov 29, 2006)

Vinnie;641413 said:


> Does it have a turbo ?
> Is it a stock exhaust ?
> Does it go away after the truck is warm?
> Does it sound like its coming from the tail pipe or a leak farther forward?
> Your probly just hearing the waste gate holding back until the engine warms up . I,ve had afew 7.3 ,s and they all do that per design.


its a 95 turbo, stack exhaust. no wastegate..

someone said its the egr and its opening and closing cause the motors cold


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## Vinnie (Dec 4, 2006)

If you don't have a waste-gated turbo then the egr valve would have to be it . you can unhook the vacuum line from the egr valve and see if the sound goes away or gets louder.


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## rob_cook2001 (Nov 15, 2008)

the 7.3 does not have a egr, sounds like the warm up valve sticking, shut the truck off, unplug it and then re-start and see if it goes away.


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## Vinnie (Dec 4, 2006)

Does it sound like this guy ? 
www.youtube.com/watch?v=hhFaHWSSdQY


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## rob_cook2001 (Nov 15, 2008)

ya if it sounds like that it would be a sticking warm up valve, had a old farm truck (96 with 290k) that did it all the time lol


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## Doakster (Aug 15, 2008)

To Clarify some things

Yes the 7.3 does not have an EGR valve

The "Warm Up-Valve" everyone is refering to is call the Exhaust Back Pressure Valve (EBPV)

This is a valve that is in the outlet side of the turbo and is solenoid operated by a few different parameter. One is Engine operating temp(the same as engine oil temp) and another is barometric pressure. Based on these parameters the PCM (computer) will tell the EBVP to close and restrict flow of exhaust out the turbo. This in effect loads up the engine to warm it up faster. When this valve is closed that is when you get the hissing noise. This should only happen when the motor is closed. When the motor warms up to operating temps the EBVP remains fully open. 

If this is not noticeable when at Idle (which it should be very apparent if it is) and only during high throttle than I would say you have something else going on. You will also notice a slight decrease in power when the EBVP is cycled closed. 

Does this hissing sound like the video that was posted? The method of unplugging the solenoid at the turbo will work to see it that is the issue as mentioned earlier


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## Silverstreak (Oct 25, 2007)

disconnect it, its a plug on the turbo driver side back by the firewall with a green and red wire i believe, i put mine on a switch and use it as an exhaust brake when i need to


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## Dstosh (Dec 30, 2003)

You can un plug the sensor. It isnt a big deal, It just helps the truck warm up when it is cold. I unplug mine because the truck has no power when it is cold.


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## Dirtboy953B (Aug 24, 2008)

7.3 powerstroke's do not have EGR valve.........Just the 6.0 and 6.4 But it sound like the EBPV is sticking i would on hook it,I did mine a long time ago


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## Ggg6 (Oct 14, 2003)

Unless I misunderstand what the OP wrote it sounds like the EBPV is working just fine. That is exactly how I would describe how one works on an OBS truck.


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## Silverstreak (Oct 25, 2007)

once the truck gets to operating temp it should be fine.....mine would do it all the time, you could let the truck sit there a half hour and then go to drive and the hissing noise would still be there and it felt like the truck had 30hp, unplugging it helped for the time being, and since ive put it on a switch i can use it when i feel the need


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## Doakster (Aug 15, 2008)

Ggg6;652848 said:


> Unless I misunderstand what the OP wrote it sounds like the EBPV is working just fine. That is exactly how I would describe how one works on an OBS truck.


No you understood it perfectly....but the OP hasn't commented back yet.


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## Tractor Plower (Feb 1, 2007)

my truck has the exact same problem, except it doesn't matter what the engine temp is, just the outside temp. in the fall/ winter my truck will make a hissing noise when between 1000 and 1700 or so RPM but it goes away when the engine has more load. it's pretty annoying!! 

-Mike


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## Ggg6 (Oct 14, 2003)

T P like was said earlier the CPU controlls the EBPV and it looks at several parameters such as ambient air temp, engine coolant temp, RPM, engine load, exhaust back pressure all of which play a part in when the EBPV closes or opens. Judging by the info you said yours is operating normal also.


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## Doakster (Aug 15, 2008)

Here is a detailed description of why and how the EBVP cycles on and off. 

EPR: Exhaust backPressure Regulator, also called EBP regulator

For quicker engine warm-up at cold temperatures. If the IAT(Intake Air Temp) is below 37°F (50°F some models) and the EOT(Engine Oil Temp), is below 140°F (168° some models) the PCM sends a duty cycle signal to a solenoid which controls oil flow from the turbo pedestal. This causes a servo to close a valve(the EBVP) at the turbo exhaust outlet. The PCM monitors the EBP(Exhaust Back Pressure) input to determine if the EPR needs to be disabled to provide power for increased load, then re-applys the EPR as load demand decreases until EOT or IAT rises. 


To simplify the factors that affect the EBVP cycling are only IAT, EOT & EBP, I had mentioned Barometric pressure affects it early but I was incorrect and it does not affect it, Barometric pressure affects fuel quantity and injection timing.


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## Tractor Plower (Feb 1, 2007)

Thanks guys, at least I have a bit more of an idea of what's going on. It gets annoying at times but if it's working properly then i'm happy. 

Thanks again!
-Mike


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