Strange Noise when cold.

[apextrans]

Got back from NC the other night & started the truck. Temp was about 26*. It runs like crap cold due to 2 dead injectors til it warms up & they come alive. Can't plug in where I keep the carhaulers. Anyway, the truck ran for about a minute & then I heard what I can only describe as a "hissing" sound coming fron under the hood. But I could also hear it at the side & rear of the truck as well as coming from the tailpipe. I lifted the hood & looked/felt around the turbo & the IC tubes, didn't feel anything. The hissing sort of pulsates as the truck runs. Goes away once the truck is warmed up. Is this normal? I don't remember any of my wreckers or rollbacks doing this, but they ranged from 97-01. I've been home since then & have kept the truck plugged in each nite with no recurrence. It has been pretty warm here though. Any ideas?

 

[Russ]

EBPV closing?

 

[FaC]

As far as I know the truck closes the EBPV (exhaust backpressure valve) and increases the idle speed to warm up quicker. You should have also seen the RPMs come up to about 1000-1100. On mine, it will stop the high idle and the hissing sound as soon as I touch any pedal.

FWIW - FaC

 

[apextrans]

I've noticed the high idle kick in other times but to be honest the hissing caught me by surprise & I dont remember if it had idled up. I did step on the accelerator to see if the pitch of the hiss changed & it did, but it didn't stop by touching the pedals.

 

[Mike]

Yup, thats the EBPV closing.

 

[apextrans]

So no problem, that's normal?

 

[Mike]

Scott, its normal if it does it during warm up and then not after the engine is warm. However, I think it is normal again if the engine is warm and then left to idle for extended periods in cold weather. I'm not 100% certain on which years and what PCM programs activate the EBPV in those conditions. But as long as its doing it upon initial start and warm up and not after warm up driving down the road, its normal.

 

[apextrans]

Cool. I'm good than. Thanks