Equus 3660 - Hand Vacuum Pump & Brake Bleeding Kit - Manual (Page 16)

14 3660
NOTE: Use the following illustrations only as a guide. These drawings
are examples based on manufacturer's specifications of 18 in. (51 cm)
Hg of vacuum at idle at sea level. The idle specifications for your vehicle
may be higher or lower (as specified by the vehicle's manufacturer) than
the ones shown. The purpose of these examples is to show the action or
fluctuations of the needle, which are indicative of engine condition
1. Normal engine (Figure 6)
An engine at idle at sea level
should show a steady needle, and a
vacuum of 15 ~ 22 in. (38 ~ 56 cm)
Hg depending on manufacturer's
specifications. Quickly opening and
closing the throttle should cause
the vacuum to momentarily drop to
below 5 in. (12 cm) Hg, followed by
a momentary rebound to approx-
imately 25 in. (64 cm) Hg, before
returning to normal 15 ~ 22 in.
(38 ~ 56 cm) Hg.
2. Intake system leak, late
ignition/valve timing, or low
compression (Figure 7)
If the gauge reading at idle is
steady but much lower than normal
(5 ~ 13 in./12 ~ 25 cm Hg), this may
be an indication of intake manifold
system leak (intake gasket, carbu-
retor base gasket, vacuum devices
or hoses, etc.). Readings of 3 ~ 8 in.
(8 ~ 20cm) Hg below normal may be
an indication of late ignition/valve
timing or worn piston rings.
3. Ignition system problems or
burned, leaky and sticking
valves (Figure 8)
If the gauge needle fluctuates very
slowly over a range of approxi-
mately 2 in. (3 cm) Hg, this may be
an indication of an ignition
problem (spark plug gap, ignition
coil/cables/cap/circuit). If the
valves are burned or leaking, the
vacuum reading will drop every
time the defective valve or valves
are inoperative. An intermittent
drop indicates sticking valves.
0
5
10
15
20
25
30
Figure 6
0
5
10
15
20
25
30
Figure 7
0
5
10
15
20
25
30
Figure 8