"Fluttering" mechanical boost gauge
 

my factory boost gauge doesn't work so i installed a mechanical gauge. Under WOT it flutters pretty wildly between 11-13psi. If I accelerate slowly and gradually build some boost it is nice and steady till i foor it. So at part throttle making 6-7psi it's steady, but at full boost it's fluttering like a scared cat. Does this sound like a bad wastegate or maybe a boost leak (aka: o-ring problem)? I have had the intercooler off several times and the o-rings appear ok. I don't hear any hissing sounds under boost indicating a vacuum/boost leak either.

Sounds like a manual or electronic boost valve thats not working right or is chattering could do that.. if there's one installed.

might be a leaking injector block? The origonal bakelite ones eventually crack and leak.

no boost controller on the car. It's supposed to have a 1 bar spring in the gate but it nevers makes over 13psi, in fact i think it only hits 13psi on the gauge do to the flutter

Outside of the gauge fluctuation, does she run nice and smooth...no misfiring/hessitation etc.? No other symptoms other than the gauge doing the funky chicken?

What's it tied into?

the car runs pretty smooth at WOT, although it seems to feel alittle soft till it hits 5000rpm at which time it feels like it makes another 30-40hp. The one brief time i had my wide band on it the car would go full rich (10.1) when i floored it but i didn't watch it all the way to redline. So maybe it's running to rich causing the boost to flutter. I didn't see if the boost gauge calmed down once the engine was over 5000rpm as i was then concentrating on the tach and road. i need another set of eyes, or maybe a dyno appointment. There's only 2 of them on my street :)

oh, the boost gauge is sourced right at the intake manifold.

Something lifts off and leaks out, acting as a pop-off valve? I would start with inspecting intercooler O-rings.