Fuel + Spark Check-list - From Hagerty - 6/23 -
I’ve given you my thorough fuel-and-spark checklist before, but here’s the short form:
* Death from fuel starvation tends to come on gradually and feels like the car is running out of gas (because it is), whereas death from lack of spark tends to be pretty binary.
* If there really is no spark, the coil isn’t firing, so when you’re cranking the engine, the tach usually sits at zero, whereas if there is spark, the tach will usually bounce while cranking.
* If you’ve got starting fluid with you, pull off the air cleaner and spray it into the carb or throttle body while someone is cranking the engine and holding the throttle partially open. If the car starts, runs for a few seconds, then dies, you’ve got spark, which means you almost certainly have a fuel delivery problem. This could be the fuel pump, a clogged fuel filter or mesh screen, a stuck needle valve on the carb float, or a cracked rubber line causing the pump to suck air instead of fuel.
* If you have no starting fluid to test with and if the car dies, but after sitting for a short while, starts and runs only to die again, the problem is likely a clogged fuel filter that gets unclogged when fuel is no longer pushing sediment up against the screen.
* If you’ve ruled out fuel, the odds are strong that there’s no spark, but you need to check. On post-mid-1990-ish cars with coil-on-plug ignitions, you can’t check for spark directly, but on old-school distributor ignitions (which are the ones where spark often fails), you can.
* If you have an inexpensive test light, connect the lead to the “+” coil terminal, stick the probe on the “-“ terminal (or switch them; it doesn’t matter), and have someone crank the engine. The test light should flash, indicating that the coil is being triggered to fire. If it doesn’t, odds are strong that either the points aren’t opening, the condenser is bad or ungrounded, or one of the wires has pulled or broken off the coil.
* If the test light does flash, pull the thick wire out of the center of the distributor cap, use rubber-insulated pliers to hold it ¼-inch from a good ground, and have someone crank the engine. If there’s no spark there, the coil may be bad (it's being triggered but isn’t firing properly), though, in my humble opinion, this is unlikely.
* If there is a spark from that center coil wire, test for a spark at the plug wires the same way. If there’s no spark there, the fault likely lies in the distributor cap, rotor, or wires.
This simple troubleshooting tree is highly effective in triaging the problem as spark or fuel, and determining the cause.
I’ve given you my thorough fuel-and-spark checklist before, but here’s the short form:
* Death from fuel starvation tends to come on gradually and feels like the car is running out of gas (because it is), whereas death from lack of spark tends to be pretty binary.
* If there really is no spark, the coil isn’t firing, so when you’re cranking the engine, the tach usually sits at zero, whereas if there is spark, the tach will usually bounce while cranking.
* If you’ve got starting fluid with you, pull off the air cleaner and spray it into the carb or throttle body while someone is cranking the engine and holding the throttle partially open. If the car starts, runs for a few seconds, then dies, you’ve got spark, which means you almost certainly have a fuel delivery problem. This could be the fuel pump, a clogged fuel filter or mesh screen, a stuck needle valve on the carb float, or a cracked rubber line causing the pump to suck air instead of fuel.
* If you have no starting fluid to test with and if the car dies, but after sitting for a short while, starts and runs only to die again, the problem is likely a clogged fuel filter that gets unclogged when fuel is no longer pushing sediment up against the screen.
* If you’ve ruled out fuel, the odds are strong that there’s no spark, but you need to check. On post-mid-1990-ish cars with coil-on-plug ignitions, you can’t check for spark directly, but on old-school distributor ignitions (which are the ones where spark often fails), you can.
* If you have an inexpensive test light, connect the lead to the “+” coil terminal, stick the probe on the “-“ terminal (or switch them; it doesn’t matter), and have someone crank the engine. The test light should flash, indicating that the coil is being triggered to fire. If it doesn’t, odds are strong that either the points aren’t opening, the condenser is bad or ungrounded, or one of the wires has pulled or broken off the coil.
* If the test light does flash, pull the thick wire out of the center of the distributor cap, use rubber-insulated pliers to hold it ¼-inch from a good ground, and have someone crank the engine. If there’s no spark there, the coil may be bad (it's being triggered but isn’t firing properly), though, in my humble opinion, this is unlikely.
* If there is a spark from that center coil wire, test for a spark at the plug wires the same way. If there’s no spark there, the fault likely lies in the distributor cap, rotor, or wires.
This simple troubleshooting tree is highly effective in triaging the problem as spark or fuel, and determining the cause.
