Brake booster vacuum requirement: 94 Lumina

Discussion in 'Domestics' started by jay, Jan 6, 2008.

  1. jay

    jay Hero Member

    Joined:
    Nov 14, 2006
    Messages:
    445
    Likes Received:
    0
    Location:
    NC
    94 Lumina Z34, 145,000 miles

    I have been chasing a rough, surge, high idle problem on this car. After " smoking" the intake with Redlines smoke machine and finding/replacing many vac leaks in hoses, car exhibited limited or no vac assist when applying brakes. Pulled booster hose from booster and installed vac gauge and found 8" of vac at idle. Pulled upped timing belt cover off and T belt is frayed and pieces are inside cover; looks like rat nest. I am concluding that timing is off and affecting vacuum. Also when starting car, almost wants to stall until warm.

    Brake booster checks good at start up with brake pedal pressed (moves downward). I get one good brake at idle while moving but then pedal is hard.
    Anyone ever seem brake booster affected by low vac? What is min vac spec for booster to work?
    Also, after going into close loop, idle is about 800 rpm. Prior to getting idle under control, idle was about 1050rpm. I believe this masked a low vac problem and provided enough vac for booster to never get depleted of vac.
    I raced idle to about 2000rpm and best vac was 17.

    Thanks for any help
     
  2. Mobile Dan

    Mobile Dan wrench

    Joined:
    Mar 1, 2002
    Messages:
    3,218
    Likes Received:
    34
    Gender:
    Male
    Location:
    Kentucky
    Replace the timing belt ASAP.

    The plastic part that connects the hose to the booster has a one-way check valve in it. Some times they fail to do their job of keeping the vacuum from leaking back into the manifold. Get a new one...they're cheap.

    Dan
     
  3. jay

    jay Hero Member

    Joined:
    Nov 14, 2006
    Messages:
    445
    Likes Received:
    0
    Location:
    NC
    Forgot to mention that I checked fuel pressure, KOEO, was 41.5psi and held pressure for 24 hours. Also hooked mityvac to vac hose going to f. Press regulator and pulled and held 10" vac with no problems. Noticed when engine idling that Fuel press only dropped 0.5psi to 40psi, so the low vac shows up in fuel pressure operation.

    Also bench tested digital EGR and it checks out. Installed block off plate over EGR opening and ran engine; no change in idle quality.

    I'm going to get a Booster check valve tomorrow.

    Thanks, jay
     

Share This Page