Tune-Up Trouble Shooting - Gas Engine Vehicles
NOTE:
This is GENERAL
information. This article is not intended to be specific to any unique situation or individual vehicle configuration. The purpose of this Trouble Shooting information is to provide a list of common causes to problem symptoms. For model-specific Trouble Shooting, refer to SUBJECT, DIAGNOSTIC, or TESTING articles available in the section(s) you are accessing.
BASIC SPARK PLUG TROUBLE SHOOTING CHARTS
| CONDITION & POSSIBLE CAUSE | CORRECTION | |
|---|---|---|
| Normal Spark Plug Condition | ||
| Light Tan or Gray deposits | No Action | |
| Electrode not burned or fouled | No Action | |
| Gap tolerance not changed | No Action | |
| Cold Fouling or Carbon Deposits | ||
| Overrich air/fuel mixture | Adjust air/fuel mixture, see ENGINE PERFORMANCE section | |
| Faulty choke | Replace choke assembly, see ENGINE PERFORMANCE section | |
| Clogged air filter | Clean and/or replace air filter | |
| Incorrect idle speed or dirty carburetor | Reset idle speed and/ or clean carburetor | |
| Faulty ignition wires | Replace ignition wiring | |
| Prolonged operation at idle | Shut engine off during long idle | |
| Sticking valves or worn valve guide seals | Check valve train | |
| Wet Fouling or Oil Deposits | ||
| Worn rings and pistons | Install new rings and pistons | |
| Excessive cylinder wear | Rebore or replace block | |
| Excessive valve guide clearance | Worn or loose bearing | |
| Gap Bridged | ||
| Deposits in combustion chamber becoming fused to electrode | Clean combustion chamber of deposits | |
| Blistered Electrode | ||
| Engine overheating | Check cooling system | |
| Wrong type of fuel | Replace with correct fuel | |
| Loose spark plugs | Retighten spark plugs | |
| Over-advanced ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Pre-Ignition or Melted Electrodes | ||
| Incorrect type of fuel | Replace with correct fuel | |
| Incorrect ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Burned valves | Replace valves | |
| Engine Overheating | Check cooling system | |
| Wrong type of spark plug, too hot | Replace with correct spark plug, see ENGINE PERFORMANCE | |
| Chipped Insulators | ||
| Severe detonation | Check for over-advanced timing or combustion | |
| Improper gapping procedure | Re-gap spark plugs | |
| Rust Colored Deposits | ||
| Additives in unleaded fuel | Try different fuel brand | |
| Water In Combustion Chamber | ||
| Blown head gasket or cracked head | Repair or replace head or head gasket | |
NOTE:
Before diagnosing an electronic ignition system, ensure that all wiring is connected properly between distributor, wiring connector and spark plugs. Ignition problem will show up either as: Engine Will Not Start or Engine Runs Rough.
BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS
| CONDITION & POSSIBLE CAUSE | CORRECTION | |
|---|---|---|
| Engine Won't Start | ||
| Open circuit between distributor and bulkhead connector | Repair circuit | |
| Open circuit between bulkhead connector and ignition switch | Repair circuit | |
| Open circuit between ignition switch and starter solenoid | Repair circuit | |
| Engine Runs Rough | ||
| Fuel lines leaking or clogged | Tighten fitting, remove restriction | |
| Initial timing incorrect | Reset ignition timing see ENGINE PERFORMANCE | |
| Centrifugal advance malfunction | Repair distributor advance | |
| Defective spark plugs or wiring | Replace plugs or plug wiring | |
| Component Failure | ||
| Spark arc-over on cap, rotor or coil | Replace cap, rotor or or coil | |
| Defective pick-up coil | Replace pick-up coil | |
| Defective ignition coil | Replace ignition coil | |
| Defective vacuum unit | Replace vacuum unit | |
| Defective control module | Replace control module | |
BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS - USING OSCILLOSCOPE PATTERNS
| CONDITION & POSSIBLE CAUSE | CORRECTION | |
|---|---|---|
| Firing Voltage Lines are the Same, but Abnormally High | ||
| Retarded ignition timing | Reset ignition timing, see ENGINE PERFORMANCE section | |
| Fuel mixture too lean | Readjust carburetor, see ENGINE PERFORMANCE | |
| High resistance in coil wire | Replace coil wire | |
| Corrosion in coil tower terminal | Clean and/or replace coil | |
| Corrosion in distributor coil terminal | Clean and/or replace distributor cap | |
| Firing Voltage Lines are the Same but Abnormally Low | ||
| Fuel mixture too rich | Readjust carburetor, see ENGINE PERFORMANCE | |
| Breaks in coil wire causing arcing | Replace coil wire | |
| Cracked coil tower causing arcing | Replace coil | |
| Low coil output | Replace coil | |
| Low engine compression | Determine cause and repair | |
| One or More, But Not All Firing Voltage Lines are Higher Than Others | ||
| Carburetor idle mixture not balanced | Readjust carburetor, see ENGINE PERFORMANCE | |
| EGR valve stuck open | Clean and/or replace valve | |
| High resistance in spark plug wires | Replace spark plug wires | |
| Cracked or broken spark plug insulator | Replace spark plugs | |
| Intake vacuum leak | Repair leak | |
| Defective spark plugs | Replace spark plugs | |
| Corroded spark plug terminals | Replace spark plugs | |
| One or More, But Not All Firing Voltage Lines Are Lower Than Others | ||
| Curb idle mixture not balanced | Readjust carburetor, see ENGINE PERFORMANCE | |
| Breaks in plug wires | Replace plug wires causing arcing | |
| Cracked coil tower causing arcing | Replace coil | |
| Low compression | Determine cause and repair | |
| Defective spark plugs | Replace spark plugs | |
| Corroded spark plugs | Replace spark plugs | |
| Cylinders Not Firing | ||
| Cracked distributor cap terminals | Replace distributor cap | |
| Shorted spark plug wire | Determine cause and repair | |
| Mechanical problem in engine | Determine cause and repair | |
| Defective spark plugs | Replace spark plugs | |
| Spark plugs fouled | Replace spark plugs | |
BASIC DRIVEABILITY PROBLEMS TROUBLE SHOOTING
| CONDITION & POSSIBLE CAUSE | CORRECTION | |
|---|---|---|
| Hard Starting | ||
| Binding carburetor linkage | Eliminate binding | |
| Binding choke linkage | Eliminate binding | |
| Binding choke piston | Eliminate binding | |
| Restricted choke vacuum | Check vacuum lines for blockage | |
| Worn or dirty needle valve and seat | Clean carburetor, see ENGINE PERFORMANCE | |
| Float sticking | Readjust or replace float see the ENGINE PERFORMANCE section | |
| Incorrect choke adjustment | Reset choke adjustment see ENGINE PERFORMANCE | |
| Defective coil | Replace coil | |
| Improper spark plug gap | Regap spark plugs | |
| Incorrect ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Detonation | ||
| Over-advanced ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Defective spark plugs | Replace spark plugs | |
| Fuel lines clogged | Clean fuel lines | |
| EGR system malfunction | Check and repair EGR system | |
| PCV system malfunction | Repair PCV system | |
| Vacuum leaks | Check and repair vacuum system | |
| Loose fan belts | Tighten or replace fan belts, see ENGINE PERFORMANCE | |
| Restricted airflow | Remove restriction | |
| Vacuum advance malfunction | Check distributor operation | |
| Dieseling | ||
| Binding carburetor linkage | Eliminate binding | |
| Binding throttle linkage | Eliminate blinding | |
| Binding choke linkage or fast idle cam | Eliminate binding | |
| Defective idle solenoid | Replace idle solenoid see ENGINE PERFORMANCE | |
| Improper base idle speed | Reset idle speed, see see ENGINE PERFORMANCE | |
| Incorrect ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Incorrect idle mixture setting | Reset idle mixture, see ENGINE PERFORMANCE | |
| Faulty Acceleration | ||
| Incorrect ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Engine cold and choke too lean | Adjust choke and allow engine to warm-up | |
| Defective spark plugs | Replace spark plugs | |
| Defective coil | Replace coil | |
| Faulty Low Speed Operation | ||
| Clogged idle transfer slots | Clean idle transfer slots, see FUEL | |
| Restricted idle air bleeds and passages | Disassemble and clean carburetor, see FUEL | |
| Clogged air cleaner | Replace air filter | |
| Defective spark plugs | Replace spark plugs | |
| Defective ignition wires | Replace ignition wire see ENGINE PERFORMANCE | |
| Defective distributor cap | Replace distributor cap | |
| Faulty High Speed Operation | ||
| Incorrect ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Defective distributor centrifugal advance | Replace advance mechanism | |
| Defective distributor vacuum advance | Replace advance unit | |
| Incorrect spark plugs or plug gap | Check gap and/or replace spark plugs | |
| Faulty choke operation | Check choke and repair as required | |
| Clogged vacuum passages | Remove restrictions | |
| Improper size or clogged main jet | Check jet size and clean, see FUEL | |
| Restricted air cleaner | Check filter and replace as necessary | |
| Defective distributor cap, rotor or coil | Replace cap, rotor or coil | |
| Misfire at All Speeds | ||
| Defective spark plugs | Replace spark plugs | |
| Defective spark plug wires | Replace spark plug wires | |
| Defective distributor cap, rotor, or coil | Replace cap, rotor, or coil | |
| Cracked or broken vacuum hoses | Replace vacuum hoses | |
| Vacuum leaks | Repair vacuum leaks | |
| Fuel lines clogged | Remove restriction | |
| Hesitation | ||
| Cracked or broken vacuum | Replace vacuum hoses hoses | |
| Vacuum leaks | Repair Vacuum leaks | |
| Binding carburetor linkage | Eliminate binding | |
| Binding throttle linkage | Eliminate binding | |
| Binding choke linkage or fast idle cam | Eliminate binding | |
| Improper float setting | Readjust float setting, see FUEL | |
| Cracked or broken ignition wires | Replace ignition wires | |
| Rough Idle, Missing or Stalling | ||
| Incorrect curb idle or fast idle speed | Reset idle speed, see see ENGINE PERFORMANCE | |
| Incorrect basic timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Improper idle mixture adjustment | Reset idle mixture, see ENGINE PERFORMANCE | |
| Improper feedback system operation | Check feedback system see ENGINE PERFORMANCE | |
| Incorrect spark plug gap | Reset spark plug gap, see ENGINE PERFORMANCE | |
| Moisture in ignition components | Dry components | |
| Loose or broken ignition wires | Replace ignition wires | |
| Damaged distributor cap or or rotor | Replace distributor cap or rotor | |
| Faulty ignition coil | Replace ignition coil | |
| Fuel filter clogged or worn | Replace fuel filter | |
| Damaged idle mixture screw | Replace idle mixture screw, see FUEL | |
| Improper fast idle cam adjustment | Reset fast idle cam adjustment, see TUNE- see ENGINE PERFORMANCE | |
| Improper EGR valve operation | Replace EGR valve | |
| Faulty PCV valve air flow | Replace PCV valve | |
| Choke binding or improper choke setting | Reset choke or eliminate binding | |
| Vacuum leak | Repair vacuum leak | |
| Improper float bowl fuel level | Reset float adjustment, see FUEL | |
| Clogged air bleed or idle passages | Clean carburetor passages, see FUEL | |
| Clogged or worn air cleaner filter | Replace air filter | |
| Faulty choke vacuum diaphragm | Replace diaphragm, see ENGINE PERFORMANCE | |
| Exhaust manifold heat valve inoperative | Replace heat valve | |
| Improper distributor spark advance | Check distributor operation | |
| Leaking valves or valve components | Check and repair valvetrain | |
| Improper carburetor mounting | Remove and remount carburetor | |
| Excessive play in distributor shaft | Replace distributor | |
| Loose or corroded wiring connections | Repair or replace as required | |
| Engine Surges | ||
| Improper PCV valve airflow | Replace PCV valve | |
| Vacuum leaks | Repair vacuum leaks | |
| Clogged air bleeds | Remove restriction | |
| EGR valve malfunction | Replace EGR valve | |
| Restricted air cleaner filter | Replace air filter | |
| Cracked or broken vacuum hoses | Replace vacuum hoses | |
| Cracked or broken ignition wires | Replace ignition wires | |
| Vacuum advance malfunction | Check unit and replace as necessary | |
| Defective or fouled spark plugs | Replace spark plugs | |
| Ping or Spark Knock | ||
| Incorrect ignition timing | Reset ignition timing see ENGINE PERFORMANCE | |
| Distributor centrifugal or vacuum advance malfunction | Check operation and replace as necessary | |
| Carburetor setting too lean | Readjust mixture setting, see ENGINE PERFORMANCE | |
| Vacuum leak | Eliminate vacuum leak | |
| EGR valve malfunction | Replace EGR valve | |
| Poor Gasoline Mileage | ||
| Cracked or broken vacuum | Replace vacuum hoses hoses | |
| Vacuum leaks | Repair vacuum leaks | |
| Defective ignition wires | Replace wires | |
| Incorrect choke setting | Readjust setting, see ENGINE PERFORMANCE | |
| Defective vacuum advance | Replace vacuum advance | |
| Defective spark plugs | Replace spark plugs | |
| Binding carburetor power piston | Eliminate binding | |
| Dirt in carburetor jets | Clean and/or replace jets | |
| Incorrect float adjustment | Readjust float setting, see FUEL | |
| Defective power valve | Replace power valve, see ENGINE PERFORMANCE | |
| Incorrect idle speed | Readjust idle speed | |
| Engine Stalls | ||
| Improper float level | Readjust float level | |
| Leaking needle valve and seat | Replace needle valve and seat | |
| Vacuum leaks | Eliminate vacuum leaks | |