2017 Hyundai Elantra 2L - P0303 Cylinder 3 misfire - VERY intermittent - Why you need a scope!

Part 2 covers overview and cautions about used ECMs
• 2017 Hyundai Elantra 2...
2017 Hyundai Elantra 2L non turbo. The car has had this problem since it was almost new. It's been to the dealership countless times where it's had many parts changed. The customer was told the next step was a fuel injector. This car sets a P0303 - Cylinder 3 Misfire. No other codes.
I looked at this car at least a half dozen times. Never once felt a misfire. I even went on a 30 minute test ride and nothing. Customer has brought it to me right away when it was acting up. Drives it right to our shop, shuts it off, I get in it within 5 minutes, fire it up and ... nothing!
Eventually I was able to make it have a slow, constant surging idle by inducing a vacuum leak. The customer said it would do that for a while then start misfiring constantly. I saw the ignition timing was going all over the place on the scan tool. It does have a two wire crank position sensor. The kind that makes its own AC voltage. When those sensors fail they produce less amplitude. At slower engine speeds the amplitude can get low enough that the ECM has a hard time detecting it. Doesn't explain why it's only ever a P0303 but gotta try something eventually...
I go to bring it in the next day and HALLELUJAH! It's misfiring! I was all nervous it would stop so I drove it in the shop and started testing as fast as I could! It turned out to be a neat problem and a quick catch with the lab scope. This would have been quite difficult without a labscope.
The information, demonstration and any content contained in this video is for informational purposes only. The user and EUrbanAutoTech makes no warranty, express or implied, regarding the effectiveness or safety of the contents of this video. In no way should the contents of the video, including the tools used, be repeated or tried by anyone. Viewers should only seek the help of a trained professional located at a licensed auto repair shop for any fix, modification, alteration, or any change to their vehicle. EUrbanAutoTech shall not be liable for any injury, damage, or loss to any person or property that may result from use of the tools, equipment, or any content contained in this video. In addition, there is no way to guarantee that the video is not altered or modified or is not in the final form submitted by EUrbanAutoTech and therefore, EUrbanAutoTech does not warrant that the video is unaltered or not modified. The links on this video to products are for informational purposes only and in no way are an endorsement of the safety or effectiveness of the particular product. Viewers understand that anything contained in this video or linked to or from this video is the sole responsibility of the viewer and in no way provides an express or implied warranty as to the safety or effectiveness of any linked tool, product, or video. Therefore, viewer agrees to release, waive, and discharge EUrbanAutoTech or anyone affiliated with EUrbanAutoTech, from any and all liability, claims, demands, actions, and causes of action whatsoever arising out of or related to any loss, damage, or injury, including death, that may be sustained by the viewer, or to any property belonging to viewer, regardless of whether the loss is linked to the use of the contents of this video, or otherwise and regardless of whether such liability arises in tort, contract, strict liability, or otherwise, to the fullest extent allowed by law.