Exhaust Backfire (Rich Fuel Mixture)

1. Access diagnosis codes. If abnormal codes are present, proceed to ``Diagnosis Code Interpretation.'' If normal code is present, proceed to step 2.
2. Check ignition timing. If timing is satisfactory, proceed to step 3. If timing is not satisfactory, adjust as required.
3. On models equipped with 2S-E, 4A-GE, 4A-GEC, 4A-GEL, 4A-GELC and 4Y-EC engines, check curb idle speed. If idle speed is satisfactory, proceed to step 4. If idle speed is not satisfactory, adjust as required.
4. On all models, check cold start injector for proper operation. If cold start injector is satisfactory, proceed to step 5. If cold start injector is not satisfactory, replace cold start injector and/or start injector time switch as required.
5. On models equipped with 2S-E, 3S-FE, 3S-GE, 4A-GE, 4A-GEC, 4A-GEL and 4A-GELC engines, ensure fuel pressure is as specified. If fuel pressure is satisfactory, proceed to step 6. If fuel pressure is not satisfactory, check pressure regulator for proper operation. Repair or replace as required.
6. On all models, check fuel injectors for proper operation. If fuel injector is satisfactory, proceed to step 7. If fuel injector is not satisfactory, check for injector leakage. Repair or replace as required.
7. Ensure spark plugs are satisfactory. If plugs are satisfactory, proceed to step 8. If plugs are not satisfactory, replace plugs as required and check compression pressure.
8. Ensure EFI electronic circuit is satisfactory. If circuit is satisfactory, test is complete. If circuit is not satisfactory, check the following:
a. Injection signal circuit.
b. Oxygen sensor.
c. Throttle position sensor.