Technical vacuum gauge - blip

[arc]

Anyone with a vacuum gauge installed, once the car is warmed. If you rev it to say 3k in neutral and then let the revs drop, does your gauge show a stronger than idle vacuum and then a quick blip up toward idle and then back down again?

Not too great at explaining what i mean, but is this just the way it happens on fiat engines, on a more powerful car it'd mean the back pressure was too high wouldnt it?

 

[HP]

yeah, if I understand correctly! It will show a higher vacuum under engine braking, then settle out under idle. You may see it fluctuate a little at idle as the speed controller does it's stuff too.

Mine runs to about -25 on overrun and settles to about -19 to -20 on idle.

 

[surfin_fella]

how did you fit it, arc? where did you attatch it?

 

[arc]

remeber the useless vacuum selector for hot/cold air feeds that you bung up when rip off the std airbox? its attached to that.

Ive had the gauge in for a while and it does the same, 25 on overrun and flutters between 19-20 on idle. Its just there is quite an obvious blip when the engine is slowing from overun, when i take my foot off, it'll drop to around 25 and then as the engine slows it'll quickly move to around 23 and then back to 25 and then fall slowly to idle (19-20)

 

[HP]

There's a fuel cutoff on overrun above a certain revs, it could be when this is kicking the fuel back in I suppose as the revs come down (wild guess..)

 

[surfin_fella]

remeber the useless vacuum selector for hot/cold air feeds that you bung up when rip off the std airbox? its attached to that.

cool, cheers

 

[arc]

that make sense, im not worried about it - just trying to sus out why it did it and the only thing i could find was about a scooby engine and if that blips like this it means back pressure is too high or the exhaust is clogged (same thing really)

i tried to see if GeX's 1242 sei does the same thing, but his vacuum gauge isnt very sensitve so wouldnt pick it up even if it did do it