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.
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[@karljustme9523]

Intresting I have same issues on My Hyundai Kona 2019. Its always cylinder 3 missfire change spark plugs and coil and it will go away for a while then come back. Just changed injector and its been working with no codes for 4 months now so fingers crossed.

[@technikusMagna]

Hey there! When I'm in such Situations, I just swap two ignition Coils. If the fault stays on the same cylinder it's often the injektor (with the M157 AMG engine in particular). And if it "travels" with the Coil it's a defective coil. Didn't watch the entire Video jet, but wanted to metion before i forget.

[@eurbanautotech]

@Tacer Animation Normally I'll swap coils on misfires as well. It's quicker and easier than pulling out the labscope. However, on this car, it took so long to get it to act up I was worried that it would stop misfiring! I didn't want to disturb anything.

[@BruceMcMoose]

My car is having the exact same issue, P0303 only happens very randomly, seems to quickly fix itself and the CEL will eventually go off. Out of interest what is the fix for something like that?

[@kzmarz5712]

@@BruceMcMoose I would like to know what the fix is too have the same problem and I’ve change both the sparks, coils, and cable, what is the fix??

[@brethart4938]

I recent bought ignition coil then what happens the car vibrates few months ago I changed my spurplugs as well so I opened cleaned erased the engine light three ago now it’s came again I scan it it’s p0303 having ignition coil and spurplugs not bad either it’s vibrating in the d mode parked it’s shaking what could be the issue.

[@sir_ken9767]

​@@brethart4938hello were you able to figure it out. Having the same issue

[@bran120]

Pretty sure mine is doing this. About 6 months ago had cylinder 3 misfire. Went ahead and changed spark plugs and coil. Now here we are looking up KZbin videos because we threw the same dang code! Thanks for the possible diagnostic but how much is it going to cost me? 😂

[@eurbanautotech]

@bran120 It's always good to try some testing before condemning the computer but I have to imagine this has happened before. These cars came with bad ignition coils. There is a TSB authorizing dealer techs to change them if they're still the original design. If your problem is a faulty computer then it is rather expensive. Unfortunately you can only write the VIN once on these computers. This means you can't install used computers. Only new ones. When we called they were back ordered and about $1000. It would've taken too long to get a dealer computer so we went with our local mobile guy that does programming. He can clone ECMs. This involves taking them apart and cloning the chips. That's the only way to get a used ECM to work. Still it's a good idea to get some testing out of the way. Would be a shame to pay for a computer if you have a faulty fuel injector or something.

[@brakahiphop]

Out of curiosity, have you guys switched to the new computer? Did it help? So painful to diagnose when it's acting up so randomly.

[@alexandercahoulan6583]

Good video

[@michellesandoval5294]

Ive taken my car in every month for the last 6 months and they cant pinpoint it. Last month they finally identified an ignition coil, which we replaced. Here i am 3 weeks later, and it's happening again😢

[@eurbanautotech]

@michellesandoval5294 Dang, that sucks. Crazy that it took so long to figure out an ignition coil. At the very least they're cheap enough to throw a new part at it. If you don't have any codes at all and it doesn't act up at the shop then things can be pretty difficult to figure out. This car here took over a year and MANY hours of me driving it before I finally got it to act up. Hopefully you can get your car straightened out soon and it goes back to being a nice, reliable car!

[@anudynasty916]

My 2017 Hyundai Elantra was doing the same thing and i changed out all the spark plugs and ignition coils. And it was still misfiring on the 3rd cylinder. I played with the wires and it stopped. Its driving fine roght now

[@stansethley3853]

What do you mean you "played with the wires"? I've changed the plugs and coils as well and still have a misfire. Maybe I can try what you did before giving up and taking it to the shop? Thanks in advance!

[@antoinehamel7077]

have done the same thing, ill test to play with the wires, tell you it work too

[@chesterodtuhan5315]

Have you fix the problem. Same symptoms of mine

[@eyeswideopen8115]

I have a 17 Sonata hybrid with only 46k miles , o7t of nowhere ✔ engine light comes on then acceleration seems like car want to die out ... ran a scanner on it & P0303 cyl 3 missfire shows , havent had the tune up done since 20k miles ( is it possible bad spark plug or clogged injector ) dang Hyundai dealership wants to charge 170 for diagnostic & are scheduled out until Aug 9th before they can even look at it which is insane iny eyes ... desperately need some help

[@brakahiphop]

As some suggested. Swipe the ignition coils (2-3 cylinders) and watch if the problem travels. If so, go buy new ignition coils and change them. Everybody can do this. If the problem do not travels. Try changing the spark plug of the 3rd cylinder. If its not fixing the issue. It might be the fuel injector or even the computer as this video demonstrated and that I can't help my friend sorry. Not a mechanic. Just an enthousiast.