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DIY: Testing all RX-8 Coils and GM LS2/Yukon coils and sparkplug wires
Coils with internal ignitors can't really be checked effectively using resistance and continuity measurements as shown in the factory service manual. If you suspect a coil or wire is intermittently failing or misfiring the preferred method is to use an electronic ignition spark tester.
I bought this one from NAPA for about $14 locally; brand/part # OTC 6589
It is essentially a special spark plug that requires the spark to jump about a 3/8" wide gap. The tester gap jump simulates a high load on the coil and wire. If either one is going bad it will almost always show up using this method.
Start the engine, bring it up to temperature, and then shut it down. Then take one plug wire off of a sparkplug and push the spark tester into the end just like a spark plug. The clip on the side of the tester is for securing it to a good grounding point. This is very important for the test to occur correctly. I used a set of battery jumper cables to ground the clip to the chassis. This allowed me to position the tester firing end where I could see it from the drivers seat with the hood up.
Once this is setup up you just crank up the engine. A good engine will fire and run with a missing plug wire regardless of position. When the engine starts a good coil and spark wire will result in a pulsing electrical spark across the tester end. Let it run for 15 or 20 seconds before shutting the engine down. Sometimes a failing coil will initially light off and then stop once the load generates internal heat within the coil body. So it needs to run a bit before shutting the engine off.
Repeat the process by replacing the sparkplug wire back on the appropriate plug and then move on to the next one until you have checked all four. If you have one or more fail you will then need to determine if it is the coil or the spark plug wire. You do this by removing the wire end from the coil, inserting the tester end into the coil output end so that the terminals touch, and then start the engine. The tester is a loose fit in the coil output end and this is where the battery cables also come in handy because the cable hand grip allows you to hold the tester in place within the coil without getting shocked after you start the engine. If the tester fires off the coil is good and the wire is bad, or possibly vice versa. Alternatively you can also swap in a proven good wire from another position and see what happens.
Repeat the tests to be sure. If the coil doesn't fire off without the wire then it may be bad, but also possibly the wiring or PCM has an issue. The simple way to test this is by swapping it with a good coil position and retest both. If the same coil still doesn't fire off you can be pretty sure that is the problem. If the previously good coil doesn't fire and the previously bad coil does fire after the position swap then you likely have a wiring or PCM issue, which is beyond the scope of this DIY.
I tried this tester with the OE Mazda coils and it worked perfectly. Found a bad OE coil that passed the service manual test, but otherwise was dead and not firing the sparkplug. The main difference between the OE coils and the LS2 coils is that the LS2 coils have a 4th ground wire that the 3-wire OE coils do not
Is there anything special about the plug? Couldn't I just take a cheap conventional plug, bend the gap open, and grip it with a jumper cable?
Used to do this kind of thing on piston engines in the old days by pulling a plug out and laying it on the block. Don't remember what I did so as to not get shocked. There's also the traditional method of grabbing the plug wires one at a time and seeing how high your elbow jumps for each. But that only works if you have a car where all the plugs are on top and easy to reach.
No. This is a special tool that is "similar" to a sparkplug, but designed to create a specific load on the ignition system that you cannot readily duplicate this way.
Even though this is a DIY thread, those whom have purchased any product directly from BHR (whether or not we actually manufacture it) receive this kind of attention and support, albeit in a one-on-one context.
I've heard nothing but great things about BHR (I can't wait for the long tube header) I made the comment only as a compliment to Team, and I used the BHR name because you're the only manufacturers of a plug-in coil kit. This is espectially handybecause of the of rarity of a failed coil, and I could see this coming in handy for such occasions. It can be frustrating to have an obscure issue and no insight.
So I managed to check out the spark tester tool linked in the first post above on the OE coils and it turns out this is probably the best way to check them. It indicated the factory T2 coil as being bad, but the coil passed the service manual test fine. It was completely dead and not firing the plug.
No. This is a special tool that is "similar" to a sparkplug, but designed to create a specific load on the ignition system that you cannot readily duplicate this way.
The only thing that is different in this tool than an over-gapped plug is the grounding clip.
I've been using this method to troubleshoot ignition systems for more than 25 years.
Originally Posted by RXeligion
BHR should give you a nice discount for this, with the number of drivers using their setup.
Why? Team didn't buy his ignition system from BHR.
Last edited by MazdaManiac; 09-14-2011 at 01:24 AM.
It's quite different actually. They make a similar tool for "standard" ignition systems that is closer to what an over-gapped spark plug is than the HEI version in my link. One of the differences os that the center electrode protrudes out of the ceramic like a regular plug on the standard version while it is down inside the ceramic by over 1/2" on the HEI version. So it has to overcome this as well as the large gap from the ceramic to the outer shell. If you simply overgap a plug you really have no idea how much load you are creating relative to the tool i.e. you are guessing at the calibration. a dead coil will be caught by anything, but a weak coil, spark plug wire, or grounding point may or may not be caught by the guessing tool game. That's exactly why they tell you not to use a spark plug. It was cheap relative to avoiding one more source of error.
To hear you tell it, you invented the internet too .... lol. As for my kit, where I got it and what it is isn't relative to the DIY.
As for my kit, where I got it and what it is isn't relative to the DIY.
Surely not. But it was relevant to the suggestion that you receive some sort of compensation for "working out" some "solution" to an inferred "problem" with the BHR system.
Last edited by MazdaManiac; 09-14-2011 at 09:33 AM.
I wish the stealership in Sarasota know how to do diagnostics like this they just charged me for 4 coils, plugs and cables. Good to know for future. I kept all the old coils so I might test them and sell the good ones.
We have pretty much vetted that issue as a collective around here and determined that the OEM coils are at least suspect when they reach 30K miles or so.
I guess I wont be selling them then, I will keep them in a box in the garage with a load of other junk I will probably never use.
plenty of people got a lot more mileage than that from OE coils, most people change them without any idea if they are good or not, using the tool in post 1 will clear some of this up. That tool is made by numerous other suppliers, originally it was/is a GM factory tool
My understanding is that a some of them (the smart ones) are using the testing tool or something similar to what I recommend. It's not unusal for a good factory technician to develop their own bag of tricks.
First, coming here from another thread, excellent tip!
Next, a couple of clarifications, based on a few decades of struggling the high-voltage devices. MM is correct in that calculating the voltage required for a given gap is rather straightforward. The voltage however says nothing about the power delivered in that spark. Charles is correct about this early-ish history of electronic ignition. The HEI (high energy ignition) is a true statement wrt classics points-condenser-coil ignitions or, god-help-us, magneto ignitions. However, too much power, eg. voltage x current in a spark is a really bad thing. The duration of the spark is also important. With the right (wrong) conditions the impact zone of a spark can raise the local temperature to levels that will vaporize anything. It can also destroy metals through a process called sputtering. Our HV power supplies are very robust (and expensive), but anything built to a cost, like auto ignitions, cannot be so robust, and also may be damaged by sparks of too much power. The solution? Properly sized resistors in the path from coil/power supply to the electrode (sparkplug). This will not change the sparkover voltage, but will limit the current (power) in the sparks.
09-06-2011 | 06:39 PM
Good write up.
