Mazda MX-6 1998, Workshop Manual

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TROUBLESHOOTING [ENGINE CONTROL FS]
19
EXHAUST SMOKE
DESCRIPTION Blue, black, or white smoke from exhaust system
POSSIBLE
CAUSE
Blue smoke (Burning oil)
• PCV valve malfunction
• Internal engine oil leaks
White smoke (Water in combustion)
• Malfunction of cooling system (coolant loss)
• Internal engine coolant leaks
Black smoke (Rich fuel mixture)
• Air cleaner restricted
• Fuel return line restricted
• Improper engine compression
• Ignition system malfunction
• Intake air system collapsed or restricted
• Excessive fuel pressure
• Injector fuel leaks
Warning
Following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read
following warnings before performing fuel system service:
• Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage. Always keep
sparks and flames away from fuel.
• Fuel line spills and leaks are dangerous. Fuel can ignite and cause serious injuries or death
and damage. Fuel can also irritate skin and eyes. To prevent this, always complete “BEFORE
REPAIR PROCEDURE” and “AFTER REPAIR PROCEDURE” described in this manual.
zr 0 1 -1 4 BEFORE REPAIR PROCEDURE
cr 0 1 -1 4 AFTER REPAIR PROCEDURE
STEP
INSPECTION
ACTION
1 W hat color is smoke coming from exhaust
system? Blue Burning oil indicated.
Go to next step.
White Water in combustion indicated.
Go to step 3.
Black Rich fuel mixture indicated.
Go to step 4.
2 Remove and shake PCV valve.
Does PCV valve rattle? Yes
Check following:
• Damaged valve guide, stems or valve seals.
• Blocked oil drain passage in cylinder head.
• Piston rings for not seated, seized or worn.
• Damaged cylinder bore.
If other driveability symptoms are present, return to
diagnostic index to service any additional symptoms.
No Replace PCV valve.
3 Does cooling system hold pressure?
Yes Check following:
• Cylinder head gasket leaks.
• Intake manifold gasket leaks.
• Engine block cracked or porous.
If other driveability symptoms are present, return to
diagnostic index to service any additional symptoms.
No Check for cause.
4 Check following:
• Air cleaner for restriction.
• Collapsed or restricted intake air system.
• Restricted fuel return line.
Are all items okay? Yes
Go to next step.
No Service as necessary. Repeat step 5.
5
Retrieve and record any continuous memory,
KOEO and KOER DTCs.
Are there any DTCs displayed?
Yes Go to appropriate DTC test.
No Go to next step.
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