Question about 1993 Cadillac DeVille
CHANGE FUEL FILTER AND CLEAN FUEL INJECTORS,CLOGGED FUEL INJECTORS WILL CAUSE ENGINE TO MISS, MAKE SURE SPARK PLUG GAP IS 0.060, LEAN MISFIRE FROM WEAK FUEL PUMP,CHECK FUEL PRESSURE SHOULD BE 40 - 50 PSI. IF EVEVY THING CHECK OUT OKAY,MISSING PROBLEM COULD BE LOW CYLINDER COMPRESSION OR INTAKE MANIFOLD AIR LEAKS.DO A COMPRESSION TEST IF NECESSARY.
Posted on Apr 08, 2011
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Posted on Jan 02, 2017
Tips for a great answer:
Refer to Intermittent Conditions before starting.
Search for bulletins.
Observe the owners driving habits.
Test the fuel system circuits for proper operation. Refer to Fuel Pump Electrical Circuit Diagnosis .
Test for low fuel pressure. Refer to Fuel System Diagnosis .
Inspect for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
Inspect for fuel in the pressure regulator vacuum hose.
Ensure each injector harness is connected to the correct injector/cylinder.
Inspect for any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. Refer to Diagnostic Aids for DTC P0172 .
Inspect for any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. Refer to Diagnostic Aids for DTC P0171 .
Test for conditions which cause an incorrect idle speed.
Throttle body tampering, excessive deposits, or damage--Refer to Fuel System Description .
Restricted air intake system
Large vacuum leak
Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the MAF sensor and the throttle body.
Inspect crankcase ventilation valve for proper operation.
Inspect the throttle position (TP) sensor and related wiring. Refer to DTC P0123 .
Monitor the 24X crank sensor and the CMP sensor signal present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Test all CKP sensor A and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Monitor the 3X parameter on the scan tool. If the 3X is not responding, inspect the CKP sensor B and circuits for intermittents. Inspect the ignition control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted, they may not set a diagnostic trouble code (DTC) immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test the exhaust gas recirculation (EGR) system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .
Inspect the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive
Inspect for proper ignition voltage output using the following steps:
Attach the J 26792 Spark Tester to engine ground.
Connect the spark plug end of the spark plug wire to the J 26792 . Leave the other end of the spark plug wire connected to the coil being tested.
Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
Crank the engine while observing the J 26792 . A spark should be observed.
Repeat the above steps for each coil.
If spark is not present at the coils, inspect for the following conditions:
Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range
5000-8000 ohms (5K-8K ohms)
Spark plug wires--Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range
Spark Plug Wire Resistance
9 686 ohms per meter (3,000 ohms per foot)
Important: : Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition voltage will arc to ground when a secondary component is faulty.
Defective ignition module
Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring
Remove spark plugs and inspect for the following conditions:
Burned or damaged electrodes
Improper heat range or reach
If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Inspection .
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