Troubleshooting no spark conditions is relatively straightforward. The same concepts apply regardless of the manufacturer of the engine. While it’s annoying to find a surprising no spark condition, by being systematic with diagnosis we can hone in on the issue pretty quickly.
No spark conditions are very common if you’re dealing with obsolete and abandoned equipment. This is to be expected.
It’s more frustrating when you pull your mower out for the spring and find a new, no spark condition. Luckily, the diagnosis is pretty straightforward. We need to isolate and test the individual components that make up the spark system.
Troubleshooting No Spark Diagnosis
For the diagnosis, we’ll need to isolate the following components for testing:
- battery
- ignition switch and starter
- spark plug
- spark plug lead and boot
- ignition coil
- timing
Tools Needed (Commissions Earned)
Battery Testing
The first culprit of a no spark condition is the battery. Obviously if the battery is dead, the machine won’t even turn over, so there’s no possibility of a spark.
If the machine is turning over slowly, then it’s possible that it’s just not creating a strong enough spark.
So hook up a battery load tester to check the battery level first, and charge it if necessary. It’s possible to have a parasitic draw that keeps depleting the battery, so read up on this post if you find your battery is constantly dying.
Ignition Switch and Starter Testing
Again, if either of these two components are faulty, then the machine won’t be turning over, so there won’t be a spark generated. This should be fairly obvious to identify.
That being said, we want to ensure a systematic approach to diagnosis, and that includes inspecting the individual components of the spark/ignition system.
For the ignition switch and starter testing, use a multimeter to ensure 12 volts are entering both sides of the switch, and the starter motor is receiving 12 volts with the ignition key in the “crank” position.
Fun fact, if the starter motor does fire and the engine cranks, then it’s probably getting 12 volts.
Spark Plug Testing
While you can certainly test a spark plug by placing the terminal end on the block, I like to use a spark plug tester. One end connects to the spark plug and the other threads into the spark plug hole.
When you crank the engine, the tester will light up if there’s a spark generated. It’s just a little bit safer and easier than trying to rest the spark plug on the block and not get shocked.
While the spark plug is out, assess the condition of it. Is it overly carbonized or oily? Either of these situations can prevent a spark from jumping the gap. Rust will also cause problems.
If the plug terminal is dirty, take the time to clean it and ensure that the gap is correct.
Spark Plug Boot/ Lead Testing
Since we’ve taken spark plug out, now is a good time to assess the condition of the spark plug boot and lead. This lead runs to the ignition coil, but if the wires are frayed at all they could be contacting the engine block and shorting out.
This will prevent the spark plug from receiving spark. Furthermore, the boot might be contaminated with rust or debris, or the plug might not be making good contact. Ensure it’s clean, just like the spark plug.
Testing the Ignition Coil (or Points)
Most newer machines have an electronic ignition coil. Older machines usually have a points and condenser ignition. These older types are notorious for getting corroded and having a no spark condition.
The points are found beneath the flywheel, but an electronic ignition is usually adjacent to the flywheel.
You’ll see two magnets on the flywheel; ensure that these are clean. Likewise, make sure that the ears that contact the flywheel are clean.
If you have a points/condenser system, remove the flywheel and the points cover. Then use a small file or emory board to clean the points themselves.
For an electronic ignition coil, there’s a few things we can test.
You’ll find a small wire that comes from the back of the ignition coil. This is the grounding wire. If you crank the engine with the wire on and there’s no spark, go ahead and remove this wire and try cranking it again.
If you now have spark, then you know that the ignition coil is good and the problem lies in the wiring of the electronic system.
If there’s still no spark, then you now know that the ignition coil is bad and needs to be replaced. Or, the gap between the ignition coil and flywheel is incorrect. Re-gap the coil before you replace it, and test it again.
Another Ignition Coil Test
Before you scrap the ignition coil altogether, there’s another test you can do with a multimeter.
Set the multimeter to Ohms to measure resistance. Then, plug the positive lead into the spark plug boot. You’re then going to set the negative lead of the multimeter on the flange of the coil where it bolts to the block.
This is the ground for the ignition coil, and you should see a reading on the multimeter. If the reading is between 2.5 – 5 Ohms, then the ignition coil is measuring a correct amount of resistance. If it is outside of these specs, then it’s time for replacing the coil.
Testing the Timing
This diagnosis is a bit of anomaly, but in the spirit of being thorough I wanted to mention it here. If the timing is off on the machine, there’s a chance that it could be creating a spark still, just at the incorrect time.
However, we’ll inadvertently be testing this because we need to remove the flywheel to access the points. At the very least, if you have an electronic coil, you can visually inspect the flywheel key while you’re doing so.
This key is a small rectangular piece of metal that secures the flywheel to the crankshaft in the correct position.
This key is relatively fragile, and it can shear off if you hit a rock or other obstruction with the mower. In the event of a sheared key, the flywheel is no longer secured to the crankshaft so the timing will be off.
Simply replace the key and you’re good to go.
Recap
In the grand scheme of things, troubleshooting no spark conditions on a Briggs and Stratton or any other small engine is relatively simple.
One thing that I enjoy about it is that there’s really no gray area. There are definitive tests we can do to isolate and diagnose the individual components to find the faults.
Did I miss something? Let me know in the comments below!
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