Boost needle vibrating

[CIverson]

Took a 2 hour trip yesterday, and once I hit the 65mph speed limit (was going 75) the boost needle would vibrate back and forth violently between about 1 or 2lbs of boost (1 or 2 is the range it would vibrate, eg. between 13 and 15 lbs. ). It would hold steady as a rock if the boost went below 9psi, but once it hit 9 and above again it started to vibrate.



I really have no clue why it would do this. The egt and transmission temp needles aren't vibrating so I would think it's not something w/ a vibe in the truck. It had happened last time I took this trip too, but went away shortly after.



Any ideas?



only engine mods are AFE and MBRP exhaust, other mods in sig link.

 

[bzingre]

Same Problem

I've had the same problem for some time. What type of gauge is it? Mine is an 35 psi Autometer. I also have a boost bolt that ports the manifold in one of the existing holes. I don't know if its the gauge or something else. I noticed the needle vibrating only after I installed the new exhaust, but I can't prove that as a cause.

 

[CIverson]

Autometer 0-35 and the boost bolt are being used.



I had also noticed the truck would make a repetitive noise pretend mmmmmmmm is the normal sound of the engine.



mmmmmmuuuuuummmmmmmmmuuuuuummmmmmmuuuuuummmmmuuuuuummmmmm.



It's a fairly slow sound compared to the rapid movement of the boost needle.

 

[dieselpilot1969]

the only thing i can think of is a loose or leaking rubber boot somewhere between the turbo and intake elbow

 

[rbattelle]

Or a faulty gauge. Any chance of trying out another gauge to see if it's any better? Has it always done this?

 

[CIverson]

Yeah, I do have a 0-60psi lying around I can try. No it hasn't always done this, only other time I noticed is on the last trip I took to this area, which is kind of odd.

 

[nickleinonen]

my autometer ultralite gauge 0-35 doesn't vibrate at all... i don't have a boost bolt however. . i drilled & tapped my intake horn

 

[MCharlebois]

mine does the same thing--almost like a hollow vibration-0-35 Autometer---does not return to 0 ... i tapped the intake horn

marcel

 

[JThiessen]

I have Banks guages, possibly made by AUtometer, and the Boost bolt. I notcied mine vibrating like that one time while towing up a mountain pass - and it only did it at about @2000 rpm/@15lbs of boost. Hasnt done it since then.

 

[GDouglas]

I had a 0-35 psi Autometer boost gauge in my old 99 3500 that developed the bouncy needle like you describe. After checking a few basics, I decided to replace the gauge and the problem was solved. My guess is the gauge is supposed to have some sort of damper spring/apparatus inside to smooth rapidly fluctuating movements. That part of the gauge must have gone bad. There is always a slight rapid pulsation present in the intake manifold due to intake valves opening and shutting rapidly. The closer your boost sample tap is to an intake valve (i. e. boost bolt), the stronger the pulsation. Good gauges are built to not respond to pressure changes that rapidly.

 

[CIverson]

Originally posted by GDouglas

I had a 0-35 psi Autometer boost gauge in my old 99 3500 that developed the bouncy needle like you describe. After checking a few basics, I decided to replace the gauge and the problem was solved. My guess is the gauge is supposed to have some sort of damper spring/apparatus inside to smooth rapidly fluctuating movements. That part of the gauge must have gone bad. There is always a slight rapid pulsation present in the intake manifold due to intake valves opening and shutting rapidly. The closer your boost sample tap is to an intake valve (i. e. boost bolt), the stronger the pulsation. Good gauges are built to not respond to pressure changes that rapidly.

I made sure all the hose clamps were tight, and no difference so it looks like I'll try replacing the guage w/ another one I have, I hope thats the problem.