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Troubleshooting In The 21st Century - Tech Talk

Engine code troubleshooting experience and modern-day diagnostic tools are invaluable, but sometimes the Internet knows best.

David Pratte
Jun 26, 2012

One of the joys of building an engine is firing it up for the first time, something we recently experienced with Project RX-8’s new Renesis rotary (the details of which you’ll find later in this issue). Although the engine ran perfectly and purred like a kitten during its first warm-up cycle, we did encounter a little hiccup during its maiden testdrive.

Modp 1207 01+troubleshooting in 21st century+cover Photo 1/3   |   The Cobb AccessPort is an incredibly powerful tool, and not just for tuning and reflashing your ECU. We used it to check the air/fuel ratio and log all the onboard sensor data while searching for the cause of what turned out to be a phantom engine misfire code.

Out on the road, the engine sounded great and appeared to be operating smoothly, since all the gauges were pointed in the right direction, but then the “check engine” light began to blink. We also noticed the idle starting to wander a bit while sitting at stoplights. A few miles later, again at a stoplight, the engine stalled.

Not all was lost, though, since the engine fired right back up, and once cruising again there were no signs of any trouble despite the blinking and then continuously illuminated “check engine” light. As my OBD-II scan tool soon revealed, the engine code was for a random engine misfire. After I talked it over with my engine builder, Joe, we thought perhaps it was being caused by the FC Turbo II spark plugs he used during final assembly (because I failed to provide some fresh Renesis plugs).

As Jeff from MazdaManiac later clarified, the Turbo II plugs are not only two steps colder than the Renesis plugs in the leading position, but the trailing plugs on the Renesis also have a different depth than the previous 13Bs. So as it turned out, the T-II BUR9EQ spark plugs were putting the spark in the wrong position for optimum combustion, especially at idle, when the trailing side is dominate.

After grabbing my ankles and paying the ridiculous retail price for a brand-new set of Renesis iridium plugs, I swapped them in with the expectation that the wonky idle, stalling, and misfire code would all be dealt with. Sure enough, the idle and stalling problem vanished immediately after the spark plug swap, but the misfire engine code persisted, even after an ECU reset. It was time to do some serious troubleshooting.

Modp 1207 03+troubleshooting in 21st century+spark plugs Photo 2/3   |   As you can see, the FC Turbo II trailing plug (left) sits deeper in the camber than the Renesis trailing plug (right). This was the source of our idle and stalling problem.
Normally I avoid the forums because they’re cluttered with so much misinformation, but the RX-8 community has some very sharp cookies.

Having sorted out more than a few engine codes in my day, I went through my usual old-school approach of bench testing everything that could cause a misfire. I started with the ignition system, but the relatively low mileage and very robust BHR coils and wires checked out, as did everything on the fuel side. I also scoured the engine bay for any sign of a loose connector, bad ground, or frayed wire, but everything looked good there, too.

That’s when it occurred to me that I was living in the 21st century and had a very powerful diagnostic tool at my disposal: a Cobb AccessPort. This amazing little device isn’t just for tuning and flashing the ECU, it also allows you to check engine codes, log data, and watch data live. During a testdrive, the air/fuel ratio looked to be spot on, and there was no sign of any unusual changes in fuel trim, ignition timing, or mass airflow. To be certain, I did a data log at idle and while cruising and accelerating, and the logs all showed no sign of a misfire.

My only move left, and the one I should have made first since the solution proved to be so simple, was to consult the Oracle. No, I don’t mean Jim Mederer from Racing Beat, I mean the Internet and more specifically Normally I avoid the forums because they’re cluttered with so much misinformation, but the RX-8 community has some very sharp cookies in it and many of them post on this forum.

So what was the fix? Resetting the ESS (engine speed sensor), which apparently throws the engine misfire code quite often after an engine swap or pulley swap (and we did both). So although I had reset the main ECU, the ESS needs a separate reset and the procedure to do so is rather comical: turn the ignition key to the “on” position and then stamp on the brake pedal 20 times in eight seconds. If you do it right, the oil pressure gauge needle will make a sweep indicating the sensor has been reset.

Modp 1207 04+troubleshooting in 21st century+dave pratte Photo 3/3   |   Troubleshooting In The 21st Century - Tech Talk

The moral of the story is, no matter how much (you think) you know and no matter how good (you think) you are at troubleshooting, sometimes there’s no substitute for the combined knowledge base that exists on the Internet. Sure, there’s a lot of crap to sift through on the web, but if you know what you’re looking for, it’s often there to be found.

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By David Pratte
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