Low Vacuum on Idle

warringtonjack

warringtonjack

Active Member
Bl00dy thing is only holding about 100-150mmHg on idle. :roll: Sounds rough, and struggles not to stall until its warmed up a bit. I've checked over everything and can't see anything obvious, so I'm just gonna have to make up a pressure testing kit. :roll:

Has anybody got any ideas about anything that I should look at first off?


Oh, also, I seem to remember someone saying that a rough idle can be linked to a non-functioning interior ceiling light. :shock: And my interior light aint working, so i'll have to check fuses, but wouldnt have thought this would cause low vac. :roll:
 
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dave

New Member
check this site:
http://www.aa1car.com/library/vacleak.htm

i usually use a carburator cleaner and spray between the intake manifold gasket and other suspected leak areas, if the leak is there the engine should raise speed or run smooth for a moment, remenber that carb cleaner is very flamable so be careful. you can use a WD40 spray too, because this one spray like bubbles that you can see if they are suck by the leak.

most of the engines on idle speed might run between 16-22 Hg of Vacuum.
 
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warringtonjack

warringtonjack

Active Member
Can comebody please confirm which pipe on the carbon canister comes from the vacuum box below the plenum! Is it pipe A or pipe B? :roll:

And whats the likely symptoms if they're the wrong way round?
 

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Fast Guy

Fast Guy

Moderators
Staff member
Vacuum is also be an indictaion of engine health. A worn engine will also have low vacuum, but don't worry about that until you've ruled out an air leak.
 
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dobby

New Member
Its pipe a because pipe b goes to the fuel tank. I thought the small pipe was a vacuum pipe.
 
Davie Houston

Davie Houston

Member
Ditch the cannister and block the 2 pipes going to the inlet. i ditched everything i could when i done the head gasket on mine their and my vacuum on idle sits right down at the 2nd last notch on the gauge.
I also put in new vacuum pipes all round aswell just to be sure everything was all new.
 
Mikey_pulsar

Mikey_pulsar

Member
warringtonjack said:
Can comebody please confirm which pipe on the carbon canister comes from the vacuum box below the plenum! Is it pipe A or pipe B? :roll:

And whats the likely symptoms if they're the wrong way round?
Click to expand...

Mate im sure that on mine its the pipe on the top that goes to the plenum?
I'll have a look for ya tomorrow 8)
 
warringtonjack

warringtonjack

Active Member
Yeah, the top pipe is defo a vacuum pipe that comes off the plenum, but there is another vac pipe that comes from the vacuum box. As dobby says, its prob the pipe marked A. Why the need for two vac pipes though? Anyway, to ditch it, I just block off pipe A and the small top pipe, and then join the two remaining pipes together? That means the fuel tank will still vent beneath the car, but won't be drawn by vacuum, is that right?
 
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dobby

New Member
Block off the two vacuum pipes and the fuel tank pipe gets connected to the chassis leg if you like. I think its an elbow joint, its hard plastic aswell.
 
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CanadianR

Member
chuck this thing on the end of one of your fmic pipes (or the turbo side of the tmic) and pressurize it to your the boost you'll be running. You will hear leak when the air starts to hiss out. It's a cheap boost leak tester but also works for the vacuum side as well.

http://www.vfaq.com/mods/ICtester.html
 
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Cambridge_pulsar

New Member
I've made a boost leak detector but when I pressurise the intake system I can't get it above approx 0.2 bar... There is no hissing or signs of any leaks so where is the pressure being lost...?
 
Davie Houston

Davie Houston

Member
Wear abouts are you putting the leak tester, ie directly onto the hose at the air filter?
Or have you mada a hose that connects directly onto the turbo?

If you are going directly onto that hose you will need to block off the oil breather pipe also, so you dont pressurise the full engine!!!!!
 
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