Measuring Dwell - Bosch FIX 7677 Mode D'emploi

connect RED test lead to negative
side of primary ignition coil. (refer
to vehicle service manual for loca-
tion of ignition coil)
4. Connect BLACK test lead to a
good vehicle ground.
5. Turn multimeter rotary switch to
correct CYLINDER selection.
6. Measure engine RPM while en-
gine is cranking or running.
7. View reading on display.
• Remember to multiply display read-
ing by 10 to get actual RPM.
If display reads 200, then actual en-
gine RPM is 10 times 200 or 2000
RPM.

Measuring Dwell

Dwell measuring was extremely impor-
tant on breaker point ignition systems of
the past. It referred to the length of time,
in degrees, that the breaker points re-
mained closed, while the camshaft was
rotating. Today's vehicles use electronic
ignition and dwell is no longer adjustable.
Another application for dwell is in test-
ing the mixture control solenoid on GM
feedback carburetors.
To measure Dwell (see Fig. 15):
Fig. 15
Typical
Ignition
Coil
Red
Black
Ground
1. Insert BLACK test lead into COM
test lead jack.
2. I n s e r t R E D t e s t l e a d i n t o
3. Connect RED test lead to DWELL
signal wire.
test lead jack.
• If measuring DWELL on breaker
point ignition systems, connect
RED test lead to negative side of
primary ignition coil. (refer to ve-
hicle service manual for location of
ignition coil)
• If measuring DWELL on GM mix-
ture control solenoids, connect
RED test lead to ground side or
computer driven side of solenoid.
(refer to vehicle service manual for
solenoid location)
• If measuring DWELL on any arbi-
trary ON/OFF device, connect RED
test lead to side of device that is
being switched ON/OFF.
4. Connect BLACK test lead to a
good vehicle ground.
5. Turn multimeter rotary switch to
c o r r e c t D W E L L C Y L I N D E R
position.
6. View reading on display.
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