Troubleshooting Tree to Diagnose Why a Car Won't Start CJC 8/14/90 Copyright (c) 1990 Cooney Applied Technology Some of the steps that will be listed may contain instructions to do things that may be dangerous to those not aquatinted with basic safety in working around cars and machinery. Be careful and do not do anything that you are not sure of how to do and how to do safely. Use this program at your own risk, the author assumes no liability for the use of this program. # Does the engine crank when the key is turned? N:>CRANKING-SYSTEM Pull a wire off of a spark plug, hold it within 1/16" of a ground, and crank the engine. Is their a fat blue spark? N:>IGNITION-SYSTEM Y:>FUEL-SYSTEM CRANKING-SYSTEM: Look at dome light with door open (or turn on headlights). Is it lit? N:>NO-POWER Turn key while watching light. Does it go out? Y:>FADE-POWER Did the light stay exactly as bright? Y:>NO-STARTER-CURRENT N:>BAD-STARTER NO-STARTER-CURRENT: Find the Starter Relay. Turn the key, does it click? N:>NO-RELAY-FUNCTION Is there at least 6V on the Starter Relay terminal connected to the battery? N:Bad cable from battery or connections. When the key is turned and the relay clicks, is there at least 6V on the Starter Relay terminal connected to the starter? N:Bad Starter Relay (contacts). When the key is turned, is there at least 6V on the Starter terminal connected to the Starter Relay? N:Cable from Starter Relay to Starter defective or bad connections. Y:Defective Starter (open). BAD-STARTER: When the key is turned, is there at least 6V on the Starter terminal connected to the Starter Relay? N:Cables from Battery to Starter Relay to Starter have high resistance connections. Y:Defective Starter (jammed). NO-RELAY-FUNCTION: Is there at least 6V on the Starter Relay terminal connected to the battery? N:Bad cable from battery or connections. Remove the wire from the Starter Relay terminal that connects to the ignition switch. Ground this terminal. Does the engine now crank? Y:Bad ignition switch or wiring. N:Bad Starter Relay (open coil). FADE-POWER: Measure the voltage directly across the battery POSTS while turning the key. Is it at least 6V? N:Battery dead or defective. Jump-start, recharge, or replace. Y:Battery connections defective or wiring from battery to fuse panel defective. NO-POWER: Measure the voltage directly across the battery POSTS. Is it at least 10V? N:Battery dead. Jump-start, recharge, or replace. Y:Battery connections defective or wiring from battery to fuse panel defective. IGNITION-SYSTEM: Pull the lead off of the distributor cap that comes from the coil. Hold it within 1/16" of a ground, and crank the engine. Is there a fat blue spark? Y:>CAP-WIRES With the ignition on, is there at least 10V on the "+" terminal of the coil? N:Either the ignition ballast resistor is defective, a fuse is blown, or the coil primary wiring is defective. Connect a voltmeter across the coil "+" and "-" terminals. Crank the engine. Is a constant (not pulsating) voltage seen? Y:>GROUNDED-COIL Did the voltmeter show a pulsating voltage? N:>NO-COIL-GROUND Ohm out the coil to distributor wire. Is it less than 50,000 ohms? Y:The coil is defective. N:The coil to distributor wire is defective. CAP-WIRES: Remove the distributor cap and rotor. Are the cap contacts or rotor damaged or badly worn? Y:Replace cap & rotor. Crank the engine, and watch to see if the rotor turns. Did it turn? N:Either the distributor is broken, or the timing chain or belt is broken. Y:Sparkplug wires are likely defective, Ohm out to verify. GROUNDED-COIL: Does your car have points in the distributor (not electronic ignition)? N:Your electronic ignition module or its pickup unit is defective. Remove the condenser and check it for shorts. Is it shorted? Y:Replace condenser. N:Points shorted or wire from distributor to coil shorted to ground. NO-COIL-GROUND: Does your car have points in the distributor (not electronic ignition)? Y:Your electronic ignition module is defective. N:Points defective or wire from distributor to coil open. FUEL-SYSTEM: Does the gas gauge show gasoline in the tank? N:Fill it up dummy! Does your car have fuel injection? Y:Your car cranks and it has spark. It is most likely the fuel injection system is not working or not receiving fuel. You had best call a mechanic to check the system, it can be complex and dangerous! Just pulling a line loose can squirt you with 50 PSI of stored fuel pressure! Problems might be a plugged fuel filter, damaged or plugged fuel lines, a defective fuel pump, engine computer or sensor problems, actuated rollover switch, bad injectors or wiring, bad pressure regulator, air flow sensor defective, etc. Remove the air cleaner and look at the choke valve or plate. If the engine is cold, it should be closed. If the engine is hot, it should be open. Does it look proper? N:Defective choke, either stuck or bad thermostatic spring or heater. Do you smell the strong smell of gasoline? N:>NO_SMELL It is probably flooded. Push accelerator to the floor and hold it there, DON'T pump it! On most cars, pushing the acceleration to the floor will also open the choke valve. If your choke valve doesn't open, use a screwdriver to block the choke open. If there is still plenty of battery charge left you can crank the engine until it starts. Don't crank continuously, you will damage the starter. Stay clear of the carburetor, the engine may backfire! If you don't want to crank, wait a FULL 2 MINUTES (or more) while holding the accelerator to the floor, don't pump it. Then, while still holding the accelerator to the floor, try to start the car. Did it start? Y:It was flooded. You probably have a choke or other carburetor problem. N:>NO_SMELL NO_SMELL: Push the choke valve open with a screwdriver. Look down the carburetor throat and pump the throttle. Does a jet of fuel squirt in the throat? Y:Well, if your car cranks, has spark, it has fuel in the carburetor, and isn't flooded, it should start. Either you gave an incorrect answer to a question , or something obscure has gone wrong. Try this program again, or call a mechanic. Remove the fuel line from the carburetor connect a piece of rubber fuel line to the end, and put the other end into a glass jar. Have a fire extinguisher handy! Crank the engine. Does fuel flow into the jar? Y:Carburetor or inlet filter defective. Reconnect the line to the carburetor. Remove the fuel line from the fuel pump side of the fuel filter and connect a piece of rubber fuel line to the end. Put the other end into a glass jar. Crank the engine. Does fuel flow into the jar? Y:Plugged fuel filter. N:The fuel pump is defective, although it is possible that instead the lines to the fuel tank or pickup in the tank are clogged.