Boost gauge flutter

[mcandmar]

This has been bugging me for a while now, every now and again cruising along on part throttle with a steady vacuum the gauge needle starts to fluctuate back and forth the thickness of the needle. At a guess were talking about a .05 bar variation.

Weird thing is it comes and goes, will fluctuate for 20-30secs, then sit rock steady for 20-30secs, over and over. Then somedays its fine.

I recently noticed it seems to do the same thing under boost, hard to reproduce but if i hold steady throttle up a hill with say .5 bar boost sometimes the needle fluctuates, and sometimes it dosent.

Any ideas?

Mark.

[Phil Payne]

It's fed off a T-piece atthe back of the engine.

Check the clips.

Those little crush-on eared clips are now stocked by B&Q.

[mcandmar]

If your thinking vacuum leak i've checked everywhere and i'm confident its all air tight.

Forgot to mention the vacuum is always rock stable at idle, i think my gauge is measured in cm of mercury (cm/hg), scale is marked 20, 40, 60. When fully warm it sits just below 40. Closed throttle when driving the vacuum gauge goes off the scale.

[Rusty]

N75 duty cycle funnies can cause this at WOT but could just be the gauge tbh, is it a decent make?

[mcandmar]

Gauge is an Autometer, dont know if they are any good or not, bought it because it matches the rest of the dials

http://www.autometer.com/cat_gaugede...earch&gid=3296

[GazzaG60]

no inline filter on gauge.

if its an autometer expect it. they are crap. accurate long lasting boost gauges cost over £100.

[s2_bo]

Mark if you want you can buy on of my heavy duty N75 valves. Maybe yours is playing up a bit. If it makes no differnce I'll obviously give you a full refund.

[nip]

I had the same problem its an easy repair I plumber my gauge into the back of the reverse inlet however this will not read properly due to the air is forced into the cylinders by then so you get fluttering repair is have the t piece at the front of the inlet worked for me

[GazzaG60]

i have 2 devices under the dash where the ecu line is. boost and boost controller. same vac point, both read identical. mine are electronic signal senders though.

saves going through the firewall.