Mazda MX-6 1998, Workshop Manual

Page: 89 / 1282

TROUBLESHOOTING [ENGINE CONTROL FS]
STEP INSPECTION
ACTION
12 CHECK MANIFOLD VACUUM WITH
EXHAUST MANIFOLD DISCONNECTED
FOR INDICATION OF RESTRICTION
• Key off.
• Disconnect exhaust system immediately
after catalytic converter.
• Repeat vacuum measurement from step
10.
• Did vacuum needle quickly rise above
54 kPa {407 mmHg, 16 inHg} with engine
rpm at 2,000?
Note
• Intake manifold gasket leak can also cause
vacuum gauge needle to remain well below
normal range.
Yes
The exhaust system restriction is downstream of exhaust
manifold.
RECONNECT exhaust system at exhaust manifold.
Go to next step.
No A restriction is present in exhaust manifold.
REMOVE vacuum gauge and tachometer.
INSPECT each exhaust port for casting flash/restrictions
by dropping a length of chain into it.
Note
• Do not use wire or lamp to check ports. Restriction can
be small enough for both to pass through but large
enough to cause excessive back pressure at high
engine rpm.
REPLACE exhaust manifold if unable to remove casting
flash/restriction.
RESET PCM to completely clear DTCs.
c r After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
13 CHECK MANIFOLD VACUUM WITH
SILENCER/TAILPIPE ASSEMBLY
DISCONNECTED FOR INDICATION OF
RESTRICTION
• Key off.
• Disconnect silencer/tailpipe component
located after the catalytic converter.
• Repeat vacuum measurement found in test
step 10.
• Did vacuum needle quickly rise above
54 kPa {407 mmHg, 16 inHg} with engine
rpm at 2,000?
Yes There is restriction in the silencer/tail pipe assembly.
REPLACE silencer/tail pipe assembly.
REMOVE vacuum gauge and tachometer.
RESET PCM to completely clear DTCs.
w After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
No
There is restriction in three way catalytic converter.
REMOVE vacuum gauge and tachometer.
REPLACE catalytic converter.
INSPECT silencer to be certain converter debris has not
entered.
RECONNECT silencer/tail pipe assembly.
RESET PCM to completely clear DTCs.
e r After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
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