Hi all,
I was driving today and I noticed a weird noise. It starts with a squeak at around 1500 RPM during acceleration, then turns into a hissing sound that continues unless I take my foot off the pedal and coast. It changes pitch as the engine speeds up, and also does this while revving in neutral. The sound seems to be coming from the passenger's side. After a while, it went away, but when I started it back up again and drove away, it came back.
Any idea what is going on?
Thanks,
Jack

 

Did it do this while the engine was cold? Or was it completely warmed up when the hissing started?

Under cold weather conditions, and when the engine is still cold, the exhaust backpressure valve (EBPV) will close off the exhaust to put an artificial load on the engine. This helps the engine to warm up faster during the winter months.

If this noise is happening when the engine is fully warm, then you have other issues.

 

Yes, the engine was cold. Then, when it warmed up, it stopped. ah ha. now it makes sense. Sorry, first winter with a diesel. I had never noticed it until today though.
Thanks
Jack

 

It shouldn't be turning on when your driving though... There is a good list off things that cause it to go off.

Like:
Hitting the throttle
hitting the brake
pressing the clutch in (if applicable)

It should not be turning on while driving...

 

I'll be interested to hear from others on this. Mine will also activate while driving slowly in town, if it is still cold. Quite a head turner with the four inch straight pipe.

 

It will engage at low engine loads if the other temperature parameters are right ( under 45° outside & under 167° engine oil temp) If your tube is clean and your sensor and regulator test out to be working correctly, install a single pole switch to stop the regulator at the turbo pedestal from closing. That's what I did years ago, and I use it a lot more than I ever thought I would.

Austin

 

just like Austin said..mine did this all the time...you should hear it with a strait piped exhaust..I hated it and disconnected it at the pedestal..I then used it as a exhaust brake..now I don't have one at all..you guy's with the hand shakers need to have the E brake set for the warm ups to work.that's why it doesn't do it while you are driving...like Curtis said..if it still does this after temps are up..then I would start looking at EBPS and tube or the AIT,, if it will ease your mind and you want to know thats what it is..un plug the EBPV at the pedestal and on a cold morning ..start her up and take her for a ride ..see if it stopped doing it..

 

I rigged up a six pole, three position switch ON/OFF/ON type so that I could either leave it in the factory mode (One of the ON positions).
Or have it disabled (Off position).
Or have it be used as an exhaust brake (The other ON position).

 

Mine has always turned on while driving when it's cold out. Not while I'm accelerating hard, but once I hit a constant speed and the TC locks up, it closes at least partially and/or modulates until my water temperature hits about 180, the it opens and stays open.

 

Exactly!

Under normal operation, the EBPV still closes or partially closes under low load situations. The operation of the EBPV relies heavily on the exhaust backpressure sensor. That is why if the tube leading to the sensor gets clogged, the EBPV stays shut at all times until oil temps come up to normal range. When the EBPV stays shut like that, you'll find it's almost impossible to even get the truck up to 25 mph.

As long as the sensor tube is clean, the EBPV should function as normal.

 

so, does this mean that my EBPV is functioning completely correctly? Or do I have to clean the sensor tube? I really hate the noise it makes, but if it's supposed to be there, I guess I can live with it.

 

If you are still accelerating normally, then it's working fine. If you find that the EBPV stays closed, and the truck runs extremely sluggish until it finally opens up, then that's usually a sign that the tube is clogged.

The hissing noise is just the normal sound it makes. If it really drives you nuts, you can simply unplug the electrical connection at the actuator, which is located at the base of the turbo pedistal. By unplugging this connector, the actuator that closes the EBPV no longer works, and it keeps the valve open permanently. There's no harm in doing this, as older diesels never had an EBPV to begin with. All it will do is set a soft code that will be stored in the PCM. You won't get a check engine light, and you'll never know there is a code thrown unless you hook up a scanner. On my truck, I completely removed the EBPV, and I haven't missed it at all.

The connector that I'm referring to sits underneath the turbo. It can be a little difficult to reach. If you look at the turbo, it is mounted on the pedistal that sits between the turbo and the block. On the front of that pedistal there is a white electrical connector with a metal hoop lock. Un-snap the hook lock, and pull the connector out. That's all it takes.

 

Do the early 99's have this as well? Mine only kicks up to 900-950rpm and I don't really hear any "jet" like sound. If i go back to the pipe I can hear it a little but that could be from the increased idle. I do have stock exhaust but from what I have heard it seems that even stock there is no mistaking it.

 

Posted a similar question a few weeks ago. Glad to hears this normal/normal. It's been cold here (Boston, MA area) for the last week...except for today 58 degrees! EBPV has been closing well after engine is up to temp during low load times (such as constant 40mph). Opens immediately upon hitting the throttle.

Pocket, you've had no problems unplugging the EBPV in CO? I'd prefer to do the same here if so. Does unpluging the EBPV take away the higher idle that kicks in during cold weather while the truck is idling?

 

bump, anyone?