jumpy vac gauge

[Pappu1]

well its wierd

was looking over an sti in weekend and noticed that the boost/vac gauge needle was shaky while sitting on idle and when driving under certain conditions (mainly just cruise with a steady accelerator pedal) the gauge wud jup around a lot

basically if the vac was say 28mmHG then the needle wud fluctuate betweem 15-20 very rapidly...

whats possible causes if anyone has seen this before

in normal driving all cars i have driven its steady....

[ADIKT]

Sounds like a faulty gauge

[Marky]

Is it a mechanical or electrical gauge?

I\'ve seen mechanical gauges flicker quite a bit on very low throttle openings - hell my new blitz one did - they need a restrictor or one of those little filter things put in the vac line to mitigate it - actually works too

Can vary depending on where the vac takeoff is from a bit too

[Pappu1]

hmm its supposed to be a new gauge...

i will put another gauge and hose and then see..

yea its a mechanical gauge....

[Marky]

Its not necessarily "broken"

I\'ve seen them flicker on cars so fast they just blur at idle

It\'s just super sensitve gauge without any dampening getting the *exact* pressure at that point in the manifold - if its close to a runner or whatever in the plenum the vacuum will jump around with that cylinder sucking in and out

Thats what liquid filled gauges and those little inline filters are for (the little 2cm disk things like you see before the sender on most electronic gauges)

[Pappu1]

u mean like a filter??

[Marky]

Haha, yes a filter if youve got one lying around (TT\'s have 4 or 5 in all their hoses?) - but try just using something with like a pinhole sized opening in it, some gauges come with a T piece that has a little brass restrictor pill thing on it to stop this - same as the restrictor pill in the wastegate line

Just dampens out the pulsing effect so the gauge stays steady - some gauges already have like a tiny pinhole opening to do this so dont need the inline restrictor or filter OR they are liquid filled which has the same result of calming it down

Todays lesson brought to you by the letter I(amboredatwork)

[Pappu1]

hmm ok will see if a restrictor will do it

[D-Style]

 Marky said:

Haha, yes a filter if youve got one lying around (TT\'s have 4 or 5 in all their hoses?) - but try just using something with like a pinhole sized opening in it, some gauges come with a T piece that has a little brass restrictor pill thing on it to stop this - same as the restrictor pill in the wastegate line

Just dampens out the pulsing effect so the gauge stays steady - some gauges already have like a tiny pinhole opening to do this so dont need the inline restrictor or filter OR they are liquid filled which has the same result of calming it downTodays lesson brought to you by the letter I(amboredatwork)

Not really. Liquid filled is to render the gauge inert during different Temps and Humidities. You must use some super thick glycerine to damper a normal Burdon tube type gauge.

[Marky]

 D-Style']

[quote name='Marky said:

Haha, yes a filter if youve got one lying around (TT\'s have 4 or 5 in all their hoses?) - but try just using something with like a pinhole sized opening in it, some gauges come with a T piece that has a little brass restrictor pill thing on it to stop this - same as the restrictor pill in the wastegate line

Just dampens out the pulsing effect so the gauge stays steady - some gauges already have like a tiny pinhole opening to do this so dont need the inline restrictor or filter OR b]they are liquid filled which has the same result of calming it down[/b]Todays lesson brought to you by the letter I(amboredatwork)

Not really. Liquid filled is to render the gauge inert during different Temps and Humidities. You must use some super thick glycerine to damper a normal Burdon tube type gauge.

TIL ^this

[lachlan]

the ac compressor is modulated on and off to only use what it needs to . was it like 30-60 sec fluctuations? . and puts more or less load on engine . idle controll opens and shuts as required to mantain idle

[Pappu1]

 lachlan said:

the ac compressor is modulated on and off to only use what it needs to . was it like 30-60 sec fluctuations? . and puts more or less load on engine . idle controll opens and shuts as required to mantain idle

yea i think is related to that..

cos does not happen all the time...

went for a blat yesterday night and was fine and all of a sudden did that

will get idle controller cleaned as a start

[Timmah]

You\'re kind of describing what my boost gauge does. Not sure what is causing it, but some days it will read steady at -51 -hng, others it will fluctuate between -45 and -50 -hng.

[lachlan]

 SP00N']

[quote name='lachlan said:

the ac compressor is modulated on and off to only use what it needs to . was it like 30-60 sec fluctuations? . and puts more or less load on engine . idle controll opens and shuts as required to mantain idle

/quote]

yea i think is related to that..

cos does not happen all the time...

went for a blat yesterday night and was fine and all of a sudden did that

will get idle controller cleaned as a start

Its entirely normal and supposed to do that . Its not a problem and it can\'t be fixed ,in regards to the AC