Since I bought this truck, it has a hissing sound that almost sounds like it is coming from the rear of the truck under light to medium throttle. As soon as I let off the throttle, it stops (Even if reving high). As soon as I rest my foot back on the throttle, the noise will come back - but only after a second or 2. I can't recall having this noise on my other '99, and wanted your valued opinion as to what it could be/if it is normal??

Also, the engine/exhaust is UNchipped and UNmodded (At least thus far).

 

I'm curious as well... I have the same thing.

 

Whats the temp. out? Its your exhaust back pressure valve working to keep motor warm. Almost gaurantee it. Put some 5" exhaust like mine and you will hear a hissing you can hardly stand the morning. (well at least I imagine my neighbor cant) o well.

 

The temp out is cold (29 this morning). I have not owned this truck in warmer weather. Does that valve stay active even when the engine is warm? Mine doesn't seem to matter if the engine is warm or cold - it does it at both times.

 

A hiss you can hardly stand? Wow. It must be bad. I have a 5 inch exhaust and the EBPV isn't bad at all - no worse than a jet on a taxiway.

 

My EBPV kicked in the other night after I'd driven it over 30 miles. Went and ate dinner and when I came back it was pretty cold out, around 25*. EBPV was switching on and off for a few minutes. That's the first time I've ever noticed it doing anything once the engine was warm, kinda took me by surprise.

That thing had me wondering if my truck was about to blow when I first got it. Fortunately I found this site not long after getting my truck so I knew (figured out eventually..lol) what it was and that it was ok.

It could well be the EBPV that is kicking in on yours too. If it goes away when you mash the go pedal that should tell you a lot.

 

It does go away when I either completely let off or completely mash the "go pedal" as you put it. So that would be the EBPV?

 

try unplugging it and see if the prob goes away. let your engine cool so you don't get burning and look down in the valley of the engine at the front of the turbo near the botton and there is a 2 wire connector going into the turbo. it has a metal clip that holds it tight just rotate the clip up and pull the connector then drive it and see how it acts.

 

My EBPV will immediately kick off when I so much as touch the brake pedal. Don't know if you can try that because it sound like yours may be coming on while you are driving which has never happenned to me. Is that what it is doing?

 

Like I said, I have to have a foot on the throttle to hear it (Can be very light to medium-heavy). As soon as I take my foot off, the noise stops. When I put my foot back on (Even if very lightly), it takes about a full second and comes back. I do not associate it with my brakes - only the throttle.

 

Dsl Lover that is your EBPV doing it's normal function. It's purpose is to make the engine labor a little at slight throttle settings and get the engine to warm up in the cool weather.

 

Thanks for that kwikk. Had me stumped as does your answer 'cause I've never heard mine do that. Gonna be listening for it.

 

If you put the truck down in low gear while the engine is still cold and cruise along 1500 RPM on a level road, it will come on hard. You can feel it holding the engine back. Open the right side window and you will be able to hear it. If you don't notice it coming on then it's most likely disconnected or not working.
But it has to be aprox 50f or below for it to come on at all.

 

I will try that. Maybe I have a problem I didn't know about. I hate those LOL.

 

I'm thinking that you guys nailed it. The temps finally got up in the low 40's this afternoonand after the engine warmed up completely, I didn't hear the noise anymore. That must be it! Thanks!