We just installed the MBPR duals exhaust on my friends 2004. It sound like there is an exhaust valve closing and opening all the time cold or hot. Exhaust is real quite and then gets a nice rumble then quite, then rumbles. What is causing this? Is there an exhaust valve somewhere on the LLY motor than could be closing and openning?


Thanks,


TimEdited by: llcustom

You don't say but it sounds like your friend has the LLY engine?


If so, there's been some discussion about that and what might be the reason for it. The LLY has a Variable Vane Turbo (VVT) which is different than the LB7. It also has EGR on all trucks, not just those with CA or NorthEast emission packaged LB7's.


The ideas are that it could be the VVT cycling, or the EGR opening and closing. No one that I've seen post has a definitive answer, but I think if it was the EGR, we might have heard something about it from the folks with LB7 engines and the EGR emission package.


Or it could be a combination of the two since the biggest reason for the use of the VVT on the LLY is to produce enough backpressure for the EGR to function.


What ever the reason, the LLY's do it, or at least mine does as well as a number of others who've written about it. It doesn't seem too noticeable until an aftermarket exhaust is installed, then you can hear it quite easily.


I think it's normal...http://www.dieselplace.com/forum/smileys/Ermm.gif

I agree with Zeeb, normal.


I think it is probably the EGR, since unplugging mine, I haven't noticed it. Of course I haven't been listening for it either, so take it for what it's worth. If I can remember my name longer than five minutes, I'll try to listen for it next time I start it up.


Dennis

I have noticed the same thing happening. I do have the EGR unplugged. Made no change since it has been unplugged. Started noticing it when I changed to an aftermarket exhaust and removed the cat/resonator. LLY 2004.5 GMC





I would describe the sound as a hissing and then when open it's nice and smooth rumble.

Surely the EGR doesn't flow enough volume to have a real effect on the overall exhaust flow. It has to be the vanes opening, then the recovery to normal as exhaust gasses regain speed out of the turbo or the vanes close back.......

llcustom,


Sounds like the VRT turbo vanes opening and then closing, pretty normal on the LLY's.


Mark @ DPPI

Unplugging the EGR throw any engine lights? Anyone feel the difference?

Unplugging the EGR throw any engine lights? Anyone feel the difference?


I see you are new here, welcome to the forum...http://www.dieselplace.com/forum/smileys/Clap.gif


The search engine works really well and it's quite easy to use, you might want to try it for some of your initial questions. The question you asked is very similar to one that generated a small thread, IIRC it's now up to 22 pages...http://www.dieselplace.com/forum/smileys/Confused.gif


Here's a link:


http://dieselplace.com/forum/forum_posts.asp?TID=13040&PN=2Edited by: Zeeb

Thanks....I'am having problems with my truck....Knocking, sputtering, and surging and a bit of white smoke.....Obviously, this , sir, is not normal. But I'am learning......I have an appointment at the dealership monday....I'm up to 12,600 miles and it recently started about a month ago...It is annoying...

nico27mp:


Unplugging the EGR wont throw any lights on a federal emissions truck.


I noticed quicker turbo response, most feel it is because the engine does not have to wait for the EGR to close to bring on the boost since the valve is already closed. I also noticed a small bump in mpg, which wasnt really suprising considering the engine was running more efficiently by not having an inert mix in with the fresh new mix to burn.


You have real problems yes, obviously that stuff ain't normal. You gonna take that baby into the dealer with all those mods on it? Maybe your dealer is Joe Cool but many would void your warranty in a heartbeat when they saw those mods.


Edited by: TxChristopher

Nico...take your juice off and see what happens....definitely remove the juice before you take it to the dealer.

Juice was removed today. i didnt take out the EGT sensor though I might before monday. The problem is: I'm heading to Springfield Mo, on thursday and will be picking up a loaded car trailer, 8500 lb combo between the trailer and the Crown vic. I could really use the extra boost in level 1 going through the Ozark mountains in Arkansas....We'll see.


Nick

Not to mention the EGT guage is priceless.