Diagnostic Index: Backfires

DETECTION CONDITION AND POSSIBLE CAUSE

8	BACKFIRES
DESCRIPTION	Sound produced from exhaust system

BACKFIRES INSPECTION

STEP	INSPECTION		ACTION
1	PRELIMINARY CHECKS Perform the following preliminary checks: Vacuum lines (check for damage and proper routing). Spark plug wire routing (proper firing order). Are all checks OK?	Yes	Go to step 2.
1		No	Service as required. Verify symptom no longer exists.
2	PERFORM PCM QUICK TEST Are any DTCs displayed during Continuous Memory, Key On Engine Off (KOEO) or Key On Engine Running (KOER) Self Tests?	Yes	Check for cause. See DIAGNOSTIC TROUBLE CODE NUMBERS .
2		No	Go to step 3.
3	CHECK SECONDARY IGNITION SYSTEM Is strong blue spark visible at each disconnected high-tension lead while cranking engine?	Yes	Check spark plugs. If OK, Go to step 4. If not OK, clean or replace spark plugs.
3		No	Go to step 4.
4	CHECK FUEL DELIVERY SYSTEM Perform fuel pressure inspection. See TEST 11: FUEL LINE PRESSURE / FUEL PRESSURE HOLD INSPECTION . Fuel line pressure: 386-386 kPa (56-72 psi), 3.0L Flex Fuel 380-517 kPa (55-75 psi) Is fuel pressure correct?	Yes	Go to step 5.
4		No	If pressure is greater than 496 kPa (72 psi), 3.0L Flex Fuel 517 kPa (75 psi): Replace fuel pump module. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. If pressure is less than 386 kPa (56 psi), 3.0L Flex Fuel 380 kPa (55 psi): Check fuel supply line for restriction.
5	CHECK FUEL DELIVERY SYSTEM Check fuel pump fuel flow. See TEST 10: FUEL PUMP INSPECTION . Did fuel system flow the required amount of fuel?	Yes	Check injector for leakage. See TEST 12: FUEL INJECTOR INSPECTION page 01-01-374. If injector leaks, service as necessary. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. If injector OK, go to step 6.
5		No	Check fuel supply line for restriction.
6	CHECK BASE ENGINE Check for base engine concerns (such as improper compression, worn camshaft/valvetrain, gasket leaks). See ENGINE COMPONENT TESTS . Is a fault indicated?	Yes	Service as required.
6		No	Go to step 7.
7	CHECK EXHAUST SYSTEM Is there a restriction in the exhaust system?	Yes	Service as required.
7		No	Go to step 8.
8	Verify test results. If OK, See DIAGNOSTIC INDEX to service any additional symptoms.