Mazda MX-6 1998, Workshop Manual

Page: 88 / 1282

TROUBLESHOOTING [ENGINE CONTROL FS]
STEP
INSPECTION ACTION
10 CHECK MANIFOLD VACUUM FOR
INDICATION OF EXCESSIVE EXHAUST
SYSTEM RESTRICTION
• Attach vacuum gauge to intake manifold
vacuum source.
• Install tachometer.
• Observe vacuum gauge needle while
performing following:
Note
• Vacuum gauge reading may be normal
when engine is first started and idling.
However, excessive restriction in exhaust
system will cause vacuum. Gauge needle
to drop to low point even while engine is
idling.
• Start engine and gradually increase rpm to
2,000 with transaxle in NEUTRAL
• Decrease engine speed to base idle rpm.
• Key off.
• Did manifold vacuum rise above 54 kPa
{407 mmHg, 16 inHg} with engine rpm at
2,000?
Yes Go to next step.
No
Manifold vacuum did not reach an acceptable level.
Excessive restriction may be present.
Go to step 12.
11 CHECK MANIFOLD VACUUM FOR
INDICATION OF MODERATE EXHAUST
SYSTEM RESTRICTION
• Vacuum gauge installed.
• Tachometer installed.
• Key on, engine idling.
• Increase engine speed gradually from base
idle rpm to 2,000 rpm with transaxle in
NEU1 RAL.
• Observe vacuum gauge needle rises while
maintaining increased engine rpm.
Note
• On a non-restricted exhaust system,
vacuum gauge needle will rise quickly to
normal range as increased rpm is
maintained.
• On a restricted exhaust system, vacuum
gauge needle will rise slowly to normal
range as the increased rpm is maintained.
Note
• As increased rpm is maintained, rate of
speed of vacuum gauge needle rising to
normal range is slower on restricted system
than on non-restricted system.
• Decrease engine speed to base idle rpm.
• Key off.
•
Is the rate of speed that vacuum gauge
needle rises back to normal range
(above 54 kPa {407 mmHg, 16 inHg})
much slower than non-restricted
system?
Yes Moderate restriction may be present.
Go to next step.
No No indications of restrictions or leaks have been detected
in exhaust system.
If DTCs P0420 and P0421 are presenting catalytic
converter is chemically inactive.
REMOVE vacuum gauge and tachometer.
REPLACE catalytic converter.
RESET PCM to completely clear DTCs.
tr After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
For further symptom diagnosis (e.g. Lack of power, Loss
of Power, or No Start).
c r 0 1 -0 1 A ENGINE SYMPTOM TROUBLESHOOTING
[FS]
0 1 -0 1 A -6 0