What should manifold vacuum be at idle?
Normal manifold vacuum on an engine running at idle speed is around 18 to 20 inches. If you have an engine at idle and your vacuum gauge reads very low, or no vacuum, you are probably connected to ported vacuum.
What would cause engine to have low vacuum?
Low vacuum can be caused by low compression, intake leak or tight valves. The gauge needle bounces around a lot-uneven compression if the vacuum reading fluctuates within the normal range.
Does ignition timing affect vacuum?
The ignition or valve timing may be retarded if the vacuum is steady but lower than normal. Low vacuum can be caused by low compression, intake leak or tight valves. If the vacuum is higher than normal, it’s a sign of advanced timing.
What is vacuum at idle?
Idle Vacuum is the intake manifold vacuum when the engine is idling. The higher the vacuum, the more closed the throttle plates and the lower the amount of air and fuel required to keep the engine running an no load. Idle Vacuum is is a measure of how well the engine can idle.
What causes high vacuum at idle?
A vacuum reading at idle that is much lower than normal might indicate leakage through the intake manifold gaskets, manifold to carburetor gaskets, vacuum brake booster or the vacuum modulator. Low readings could also be caused by very late valve timing or worn piston rings.
How do you check a manifold vacuum?
Doing The Vacuum Test:
- Connect the vacuum gauge hose, as close to the intake manifold as possible and start the engine.
- Run the engine long enough, to reach normal operating temperature.
- Note the location and action, of the vacuum gauge needle.
What should timing be at idle?
The timing can vary between 2 and 12 degrees BTDC, the recommended spark plugs are different and even the plug gaps vary. In most cases starting out with 12 degrees of initial advance is about right. The initial timing should be 4 degrees before top dead center (BTDC).
Why is vacuum high at idle?
Can dirty injectors cause high idle?
Dirty fuel injectors are only one of several engine problems that can result in rough idling and engine stalling. If you notice these issues in your car, come in for a Complete Vehicle Inspection.
Why is my engine idling high?
In modern vehicles, engine idle speed is most often controlled by the idle air control (IAC) motor. When your car’s throttle is malfunctioning, this can cause your car to stall or idle high. Often this is a result of dirt buildup in the air intake. Other times it can be a problem with a cracked intake tube.