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Amroybal911
Samba Member
Joined: November 10, 2012
Posts: 16
Location: Moses lake, Wa
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 Posted: Sat Nov 17, 2012 9:30 am Post subject: Low vacuum in 412 |
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| It seems that I might be having a bad vacuum leak somewhere! I checked all the obvious location around the air distribution unit! I checked the compression on 4th cylinder it 120psi! Any other ideas for low vacuum? |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21521
Location: Oklahoma City
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| Posted: Sat Nov 17, 2012 10:56 am Post subject: |
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There are a whole SLEW of places this can leak. First question is it D-jet, L-jet or carburetted?
Also why are you supposing that you have a large vacuum leak? What are the symptoms?
You can have seriously poor vacuum signature...for instance on D-jet....by having erratic fuel pressure (I'll explain later)
Vacuum leaks:
Intake runners to head (gasket and phenolic spacer)
Injector o-rings (small but significant in effect on D-jet)
Runner boots that connect to the plenum
Any hose on the plenum
The AAR hoses may leak and the regulator may not close
On D-jet...the PCV valve in the oil baffle is a major vacuum leak source
The o-ring between the TB and plenum...very common leak point
The cork gasket on the oil filler/baffle
Every vacuum hose in the car connects o the plenum at some juncture. Clamp them all and make sure there are no cracks.
Check the vacuum dashpot for the throttle on automatic cars and also the vacuum advance unit.
make sure your valves are adjusted spot on. If you have power brakes, check the hard tube, soft tube and check valve. Ray |
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