Diagnostic Procedure

WARNING: This page is about a different car, the 2005 Mazda MX-5 Miata. However, it is still accessible from the selected car via links, so may be relevant.

NO.14 POOR FUEL ECONOMY [BP, BP WITH TC] DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	Inspect following: Contaminated air cleaner element Transmission fluid level Fuel quality Coolant level Are all items okay?	Yes	Go to the next step.
1		No	Service as necessary. Repeat Step 1.
2	Connect WDS or equivalent to DLC-2. Turn ignition switch to ON. Retrieve any DTC. Is "PASSED" displayed?	Yes	No DTC displayed: Go to the next step.
2		No	DTC displayed: Go to appropriate DTC test.
3	Connect WDS or equivalent to DLC-2. Access ECT PID. Drive vehicle while monitoring PID. (See PCM INSPECTION ) Is PID within specification?	Yes	Go to the next step.
3		No	Inspect for coolant leakage, cooling fan and condenser fan operations or thermostat operation.
4	Inspect variable valve timing operation. Is variable valve timing operation okay?	Yes	Go to next step
4		No	Repair or replace malfunctioning parts.
5	Is strong blue spark visible at each disconnected high-tension lead while cranking engine?	Yes	Inspect for following: Spark plugs malfunction CMP sensor is improperly installed. Trigger wheel damage on camshaft Open or short circuit on CMP sensor Open or short circuit between CMP sensor and PCM terminal 3V Repair or replace malfunctioning part. If okay, go to the next step
5		No	Inspect following: High-tension leads Ignition coil and connector
6	Install fuel pressure gauge between fuel filter and fuel distributor. Start engine and run it at idle. Measure fuel line pressure at idle. Is fuel line pressure correct at idle? Fuel line pressure 370-420 kPa {3.7-4.3 kgf/cm2, 53-61 psi}	Yes	Go to the next step.
6		No	Zero or low: Inspect FP circuit. Inspect for open FP relief valve. Inspect for fuel leakage inside pressure regulator. Inspect for clogged main fuel line. Inspect pulsation damper. High: Inspect pressure regulator for high pressure cause. Inspect for clogged fuel return line.
7	Remove and shake PCV valve. Does PCV valve rattle?	Yes	Go to the next step.
7	Remove and shake PCV valve. Does PCV valve rattle?	No	Replace PCV valve.
8	Is there restriction in exhaust system?	Yes	Inspect exhaust system.
8	Is there restriction in exhaust system?	No	Go to the next step.
9	Is brake system functioning properly?	Yes	Go to the next step.
9	Is brake system functioning properly?	No	Inspect for cause.
10	Inspect MAF sensor for communication. Is there any contamination?	Yes	Replace MAF sensor.
10		No	Go to the next step.
11	Is engine compression correct?	Yes	Inspect for valve timing.
11	Is engine compression correct?	No	Inspect for cause.
12	Verify test results. If okay, return to diagnostic index to service any additional symptoms. If malfunction remains, inspect related Service Bulletins and/or On-line Repair Information and perform repair or diagnosis. If vehicle is repaired, troubleshooting completed. If vehicle is not repaired or additional diagnostic information is not available, replace PCM.