Small Engines (Lawn Mowers, etc.): GX670

Question
QUESTION: I have a Honda GX670 engine that I suspect the coils are bad. The specs say they should have a resistance of 5-7K ohms. Unless I'm testing it wrong, I'm getting a reading of about 18K. So I ordered two new coils. When they arrived I tested them and they too are reading 18K ohms. At least one of them looks like a used coil.

I am wondering if you could verify that I am doing my test correctly or if they sent me two faulty coils. I have set my multimeter at 20K and put one probe on the spark plug connection and the other on one on the other post.

Thanks!

ANSWER: The URL below shows how to test coils:

https://www.youtube.com/watch?v=uOoDbQ05m98

Why don't you dis-connect the little wire connected to the modules, remove the spark plug from the engine, then connect the spark plug to the spark plug wire and check for spark.

All you need to do is make sure the spark plug is touching a metal engine part, crank the engine and see if you have spark...make sure the small wires from the coils it dis-connected.

Eric

---------- FOLLOW-UP ----------

QUESTION: Thanks, Eric. I watched several YouTube videos on how to test coils, including the link you sent, so I think I am doing it correctly. I know I am getting spark. It's when the engine gets hot that it starts to have trouble. Once it cools down I'm alright again until it gets hot. That's why I'm suspecting coil failure. I am hoping to find some way to verify if I have received defective coils before I install them.

Answer
It can be very difficult to troubleshoot defective coils that fail when they get hot.  FYI, I have only found 1 or 2 coils that failed when hot...aka, it is pretty rare.

I'd recommend you buy a Briggs & Stratton 19368 Ignition Tester, check Ebay, as this tool helped me determine a coil that failed when hot.  As soon as the engine stopped, I immediately connected the tool to check for spark...and there was no spark visible in the tool when the engine stopped when it was hot.

There is a newer tool on the market for testing ignition systems. I have used it to check for spark and it works ok but I have not verified if it works to really test the coil...I know the Briggs tester works very well for testing spark.

Google "Check Spark Engine Ignition Analyzer Model CS-2020" for the newer tool.

A Megger might help to determine the coil insulation but not too many shops have a Megger and many don't even know what they do or how to use them.

It is difficult to perform a resistance test after the engine is hot as you can't easily access the coils when the engine is assembled.

I would go ahead and order the Briggs tool and have it ready to test for spark when the engine stops.

Have you tried running the engine with the small ignition module wire dis-connected?  This will isolate the rest of the mower's electrical system from the ignition system to make sure there is not some other component causing the spark to fail.

Does the engine have a low oil sensor?

Eric