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High vac on idle
simon04 - 21/4/21 at 09:54 PM

Hi all,
Chap I've been chatting to is having issues with itbs.
He's got a reading of 14kg at 800rpm
What would cause it to be so high?
He's running Jenvy on a silver top zetec

Nile_rt - 22/4/21 at 06:23 AM

I wouldn't worry about what the reading is as long as each cylinder is roughly the same. But high vacuum is a sign of a strong engine with no air leaks

adithorp - 22/4/21 at 06:41 AM

Are all 4 tb's the same?
Could be they need balancing. If the one he's taking the reading on has the throttle closed off more than the rest, it'd give a high reading.
If they're all the same don't worry.

chillis - 22/4/21 at 09:18 AM

It depends where the vacuum is being measured. At idle the throttle plate is almost shut so downsteam of the throttle plate is naturally a high vacuum as the engine tries to draw in air past the throttle plate. A distributor vacuum take off is positioned just by the throttle plate so sees a low vacuum at idle and then the vacuum goes up as the throttle plate moves off idle.

coyoteboy - 22/4/21 at 11:35 PM

High vacuum is what you would expect at idle.

My 2ltr turbo has vac levels of 20-30kpa (absolute) at idle.

[Edited on 23/4/21 by coyoteboy]