Alright, I did the search thing and found some interesting info, but nothing exactly like I am seeing.

Anytime I get boost over 12 psi up to about 30 psi, the needle in the gauge jumps around like crazy. It is much worse under load, towing about 6k lbs. I have a mad ecm, boost fooler plumbed into the wastegate. The truck has been running this way for about 1/5 to 2 years and never ever had any problem. The boost gauge is an Autometer and the truck only has 40k miles on it. It started yesterday on a pretty long pull up a slight grade with a trailer in tow. I noticed the gauge and thought...thats strange. Below 12 psi boost, the needle is steady. I checked all the hoses and they all seem tight, I checked the plastic line and it seems ok too. I took the air filter hose off of the front of the turbo and there is slight play side to side in the shaft, maybe less than 1/16" and there is zero play in and out. There are no signs of rubbing and the turbine blades look perfect.

Also, I notice everytime I lug the truck down I can hear what seems to be a rattle in the exhaust. I hear the same noise when I shut the truck down....I swear the sound is coming through the exhaust. And sometimes just when the truck is idling I can hear what seems to be a rattle. I climbed under it and checked everything I could find and nothing is loose or rubbing anywhere near the exhaust. Any help or suggestions would be appreciated before I call the dealer.

Thanks.

 

I've got the same thing with my boost guage, I believe that the cause is that every time the intake valve opens and the piston goes down the air pressure in the maniford drops because of the mass of air that is entering that cylinder. When that valve closes the air pressure rises back up just as another cylinder starts to take some air in. Thus the guage fluxuating back and forth quickly because thats what the air pressure is doing inside the intake manifold. I noticed that the higher the pressure my turbo is putting out the more fluxuating the boost guage does. At its max, I've only see the boost guage vary 3-4 psi when it is fluxuating.

With your exhaust, I had the same problem when I put my strait pipe on...I hard mounted it to the chassis so there was no rubber hangers for the pipe to flex a little bit when I got on it or shut her down. Eventually a mount would break and cause a loud vibration noise until I welded it back together. I have since then used rubber hangers to mount my exhaust...and guess what? no more rattle.

 

Acutually I cant say that my boost guage fluxuates all of the time...I went out cruising last night after I posted my previous post. I took the boost up to 25-26 psi. and no fluxuation at all. I know it has done it before...but last night it didnt at all. Not sure why

 

My gauge made a rattling sound when I got on it or made it climb rapidly. I put a snubber on it and it fixed it. I guess it was getting too much air too fast.

 

It definetly not the gauge making the noise, it is coming from the exhaust. I checked all the hangers and they are all tight. I cant for the life of me find anything other than the turbo shaft moving left to right, up and down....still searching for answers.

 

Well, last night I replaced the gauge line...no change. I also checked all the hoses from the intercooler...all were fine. I checked the air filter...no issues there. I checked the exhaust completely for any area of possible contact...none. I looked for obvious signs of exhaust leaks...none.

I need some help from you guys as to what to look for next. I looked all around the turbo and the wastgate for any obvious signs that something wasnt right, but nothing seemed out of place.

It runs the same as before, boost builds fine, power is fine...But everytime I turn it off, I get a rattle type of noise and I swear it is from the exhaust. And sometimes just idling I can hear it. I am postponing taking it to the dealer as I am not confident they have a good diesel mechanic. And the gauge still flutters at any boost above 12 lbs. Any help or suggestions are appreciated.

Tim