Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda RX-8. However, it is still accessible from the selected car via links, so may be relevant.

N0.14 POOR FUEL ECONOMY DIAGNOSTIC PROCEDURE

STEP	INSPECTION	RESULTS	ACTION
1	Does the engine knock/ping/detonate?	Yes	Go to the symptom troubleshooting "No. 13 Knocking/pinging/detonation-Acceleration/cruise". (See NO.13 KNOCKING/PINGING/DETONATION-ACCELERATION/CRUISE .)
1	Does the engine knock/ping/detonate?	No	Go to the next step,
2	Inspect for the following: Air cleaner element for contamination Air suction at intake-air system (between MAF sensor and intake ports) ATF level (AT) Fuel quality Coolant level Brake dragging Clutch slippage (MT) MAF sensor installation Are all the items normal?	Yes	Go to the next step.
2		No	Service if necessary. Repeat Step 2.
3	Connect the WDS or equivalent to the DLC-2. Turn the ignition switch to the ON position (Engine off). Retrieve any DTCs. Are there any DTCs displayed?	Yes	DTC is displayed: Go to the applicable DTC inspection. (See DTC TABLE .)
3		No	No DTC is displayed: Go to the next step.
4	Access the ECT PID. Drive the vehicle while monitoring the PID. (See PCM INSPECTION .) Is the PID within the specification?	Yes	Go to the next step.
4		No	Inspect for coolant leakage, cooling fan operation or thermostat operation.
5	Is a strong blue spark visible at each disconnected high-tension lead while cranking the engine?	Yes	Inspect for the following: Spark plugs malfunction Eccentric shaft position sensor is improperly installed. Pulse wheel damaged on eccentric shaft Open or short circuit on eccentric shaft position sensor Open or short circuit between eccentric shaft position sensor and PCM terminal 2U or 2X Repair or replace the malfunctioning parts. If normal, go to the next step.
5		No	Inspect for the following: High-tension leads Ignition coils and connectors
6	Perform the fuel pump speed control operation inspection. (See FUEL PUMP SPEED CONTROL OPERATION INSPECTION .) Does the fuel pump speed control operate properly?	Yes	Go to the next step.
6		No	Repair or replace the malfunctioning parts, according to the fuel pump speed control operation inspection results.
7	Inspect the MAF sensor for contamination. Is there any contamination?	Yes	Replace the MAF sensor.
7		No	Go to the next step.
8	Connect the WDS or equivalent to the DLC-2. Access the MAF, O2S11, O2S12 and IAT PIDs. Are the PIDs values normal? (See PCM INSPECTION .)	Yes	Go to the next step.
8		No	If the MAF PID is not as specified: Inspect the MAF sensor. (See MASS AIR FLOW (MAF) SENSOR INSPECTION .) If the O2S11 PID is not as specified: Inspect the front HO2S. (See FRONT HEATED OXYGEN SENSOR (HO2S) INSPECTION .) If the O2S12 PID is not as specified: Inspect the rear HO2S. (See REAR HEATED OXYGEN SENSOR (HO2S) INSPECTION .) If the IAT PID is not as specified: Inspect the IAT sensor. (See INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION .)
9	Inspect the knock sensor. (See KNOCK SENSOR (KS) INSPECTION .) Is the knock sensor normal?	Yes	Go to the next step.
9		No	Replace the knock sensor. (See KNOCK SENSOR (KS) REMOVAL/INSTALLATION .)
10	Visually inspect the exhaust system part. Is there any deformed exhaust system part?	Yes	Replace the suspected part.
10		No	Go to the next step.
11	Disconnect the fuel line quick release connector and install the fuel gauge to the fuel line. Start the engine and run it at idle. Measure the fuel line pressure at idle. Is the fuel line pressure correct at idle? (See FUEL LINE PRESSURE INSPECTION .)	Yes	Go to the next step.
11		No	Zero or low: Inspect the fuel pump relay and the fuel pump circuit. Inspect for clogged fuel line. If normal, replace the fuel pump unit (See FUEL PUMP UNIT REMOVAL/INSTALLATION .) High: Replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
12	Inspect the fuel injectors for the following: (See FUEL INJECTOR INSPECTION .) Leakage Injection amount Are the injectors normal?	Yes	Go to the next step.
12		No	Replace the fuel injector. (See FUEL INJECTOR REMOVAL/INSTALLATION .)
13	NOTE: The following test is for A/C equipped models. Go to the next step for the A/C non-equipped models. Perform the A/C Cut-off Control inspection.(See A/C CUT-OFF CONTROL SYSTEM INSPECTION .)Does the A/C cut-off control operate properly?	Yes	Go to the next step.
13		No	Repair or replace the malfunctioning parts, according to the A/C cut-off control inspection result.
14	Inspect the engine compression. (See COMPRESSION INSPECTION .) Is it normal?	Yes	Inspect the eccentric shaft bypass valve.
14		No	Go to the next step.
15	Perform the metering oil pump control inspection. (See METERING OIL PUMP CONTROL INSPECTION .) Does the metering oil pump control operate properly?	Yes	Go to the next step.
15		No	Repair or replace the malfunctioning part according to the inspection results. After that overhaul or replace the engine. (See ENGINE REMOVAL/INSTALLATION or OVERHAUL - 1.3L (13B-MSB) .)
16	Check the engine oil condition. Is the engine oil low viscosity and/or is there a gasoline odor?	Yes	Replace the engine oil. Inspect the ECT sensor and the related wiring harnesses. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION .) After that overhaul or replace the engine. (See ENGINE REMOVAL/INSTALLATION or OVERHAUL - 1.3L (13B-MSB) .)
16		No	Go to the next step.
17	Inspect the oil pressure. (See OIL PRESSURE INSPECTION .) Is the oil pressure within the specification?	Yes	Go to the next step.
17		No	Repair or replace the malfunctioning part according to the inspection results. After that overhaul or replace the engine. (See ENGINE REMOVAL/INSTALLATION or OVERHAUL - 1.3L (13B-MSB) .)
18	Turn the ignition switch off. Disconnect the fuel line quick release connector and install the fuel gauge to the fuel line. Start the engine and run it at idle. Measure the fuel line pressure at idle. Is the fuel line pressure correct at idle? (See FUEL LINE PRESSURE INSPECTION .)	Yes	Go to the next step.
18		No	Replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION .) After that overhaul or replace the engine. (See ENGINE REMOVAL/INSTALLATION or OVERHAUL - 1.3L (13B-MSB) .)
19	Check the oil pipe between the metering oil pump and the metering oil nozzle. Is there air and/or clogging in the oil pipe?	Yes	Inspect and repair for leakage and/or clogging in the oil passage at the engine. After that overhaul or replace the engine. (See ENGINE REMOVAL/INSTALLATION or OVERHAUL - 1.3L (13B-MSB) .)
19		No	Overhaul or replace the engine. (See ENGINE REMOVAL/INSTALLATION or OVERHAUL - 1.3L (13B-MSB) .)
20	Verify test results. If normal, return to the diagnostic index to service any additional symptoms. If the malfunction remains, inspect the related Service Bulletins and/or the On-line Repair Information and perform the repair or diagnosis.