One of the things that I am often asked about is the validity of sparkplug testers. I think the kind that you can buy very inexpensively at most automobile parts stores that have a lamp that illuminates in them when the spark fires are great. They install by simply pulling the sparkplug wire off of the sparkplug and sticking the tester in series with it. One end of the tester has a plug on it that fits on the sparkplug where the wire was pulled off and the other end fits in the “cup” that was pulled off of the sparkplug. The neat thing about it is that you can actually run the engine with it installed and keep an eye on it to see what is going on. Obviously, if there is no spark because of an ignition problem, there’ll be no lighting of the tester, but if there is spark, you can actually see it very easily. I have even had situations where the problem that I was facing was intermittent, and the tool became almost irreplaceable. I could put the tool in place and drive the cart while watching the tool. I use a little “half seat” that I made out of a piece of plywood to sit on after removing the seat. When the cart “croaks”, I can immediately see if the problem is due to loss of spark or something else. We’ll call this type of tester a “lighted tester”.
Prior to finding one of these testers, I had several other testers, but they all worked similarly. They attached with some type of a clip to “ground” on one end and then the other end went to the cup that had been pulled from the sparkplug. The idea is to watch the tester while spinning the engine over and observe the spark (if there is one) jumping across the tester. So, the engine can’t start, even if the spark is fine, because the sparkplug wire is no longer attached to the sparkplug, but to the tester instead. We’ll call this type of tester a “non-lighted tester”.
My biggest issue with both types of testers is that sometimes the spark is there, but not strong enough. I’ve found that with both the lighted tester and the non-lighted tester, you need to develop an “eye” for what a good spark actually looks like. I always recommend that when someone gets a spark tester, the first thing they need to do is to hook it up to a GOOD RUNNING engine and take a good look at it in normal operation.
With the non-lighted tester, the spark that is jumping across its gap should be well defined, blue-white and very visible, even in broad daylight. A weak spark will usually be red or orangish in color and barely visible in daylight. Most of the better non-lighted testers have a way to adjust the size of the gap that the spark is required to jump across. That is another good way to learn about the strength of the spark. Ideally, you could go to a good working engine and keep adjusting the gap wider and wider until the spark could no longer make the jump. That would tell you just how far the good spark could go for before the gap got too wide. The testers usually have a scale calibrated in thousandths. Just how far the spark will jump will, however vary from engine to engine, but it is a good exercise to do on a few good running engines to get familiar with what is “normal”. A sparkplug gap is usually set at around .035 inch somewhere, so if the spark will jump at least twice that (.070), it should be fine. I’ve had engines where the spark could actually jump over .100 inch. Once again, if you are using this type of tester, take a good look at a healthy spark and that will become your “standard” for evaluating other situations where the spark is in question.
With the lighted tester, the difference in coloration will not be the same, because of the light source that is being used in the tester. I believe that the bulb is usually a form of “neon” in the lighted testers and tend to light the same color with either a weak or a strong spark. However, there will be a very obvious difference in the intensity of the light being emitted. It will take a little practice, but this type of tester is very usable in determining whether the spark is strong enough or not.
Remember, the best way to get familiar with any new electronic or electrical tool is to start with a known good engine to get some experience with it.
I tend to use the lighted tester most of the time, but if I have any question as to the integrity of the spark, I will go back to the un-lighted tester and see just how far the spark will jump. Good luck, Ron.
For information about books written by Ron Staley about both electric and gas driven golf carts and their repair, visit the following links.
Electric Golf Cart Repair, both as an eBook and in Hardcopy:
Book: Ronald L Staley: 9780578560557: Amazon.com: Books
Gas Golf Cart Repair, both as an eBook and in Hardcopy:Gas Golf Cart Repair Book: Ron Staley: 9798987911303: Amazon.com: Books