Mazda MX-6 1998, Workshop Manual

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TROUBLESHOOTING [ENGINE CONTROL FS]
STEP INSPECTION
ACTION
28 Crank engine for five seconds.
Does pressure drop more than 34 kPa {0.35
kgf/cm2, 5 psi} by end of five second crank
cycle?
Yes Go to next step.
No
Check resistance of fuel injector(s).
If resistance is okay, check following:
• Fuel injector drive signal.
• Injection flow rate.
• PCM.
If resistance is not okay, check following:
• Open circuit in fuel injector circuit.
29 Disconnect vacuum hose between purge
control solenoid and intake manifold from
solenoid side. Plug opening end of vacuum
hose.
Attempt to start engine.
Is starting condition improved?
Yes
Check if purge solenoid valve sticks to open mechanically.
Check evaporative emission control system.
No
Go to next step.
30 Is air leakage felt or heard at intake air system
components while racing engine to higher
speed?
Yes Repair or replace.
No Go to next step.
31 Check engine condition while tapping EGR
valve housing. Does engine condition
improve?
Yes
Replace EGR valve.
No Go to next step.
32
Is engine compression correct? Yes Check valve timing.
No
Check for causes.
33 Verify test results. If okay, return to diagnostic index to service any additional symptoms.
6
SLOW RETURN TO IDLE
DESCRIPTION Engine takes more time than normal to return to idle speed
POSSIBLE
CAUSE
• Malfunction of ECT sensor
• Thermostat stuck to open
• Throttle body malfunction
• Air leak from intake air system
STEP
INSPECTION
ACTION
1 Retrieve and record any continuous memory,
KOEO and KOER DTCs.
Are there any DTCs displayed?
Yes DTC d isp la ye d :
Go to appropriate DTC test.
No No DTC d isp la ye d :
Go to next step.
2
Make sure A/C switch is in OFF position.
Place vehicle in park or neutral.
Connect NGS tester to DLC.
Access ECT V PID.
Start engine and record ECT voltage reading
every 60 seconds.
Note
• When ECT voltage reverses direction trend
or changes slightly (0.03 volt or less),
thermostat has opened.
Is thermostat opening voltage within range?
Yes Engine coolant temperature and thermostat are okay.
Go to next step.
No Remove thermostat from engine and verify thermostat
operation.
If temperature gauge on instrument cluster is normal but
ECT V is not same as temperature gauge reading, check
ECT sensor.
3 Is throttle body free of contaminated? Yes Check for air leaks from intake air system components
while racing engine to higher speed.
No Clean or replace throttle body.
4 Verify test results. If okay, return to diagnostic index to service any additional symptoms.
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