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I have a 2018 Elantra constant misfire at idle off idle goes away. I have swapped coils, injectors and plugs with good cylinders misfire stays on #3. I have scoped injectors and monitored injection time with scanner at idle good cylinders at 2.5 ms number 3 at 1.5ms on time? If I go off idle they all even out at 1.6ms and no misfire. If Introduce propane thru throttle body misfire goes away. I took off intake to inspect variable intake flaps all good. The gasket was caved in on 3 so pulled it off and reinstalled looks even but I ordered new one with plugs to reinstall intake. Also took PICO capture of running compression the good cylinders show like 5 small 1 lb pulses on exhaust the number 3 shws only 2 pulses like exh valve closing earlier? I also got known good car cam crank capture shows about 3 deg difference crank signal to exhaust cam signal when comparing to misfire car. Lot of questions but did a lot off test before I post. Can the PCM reduce on time to one cylinder because PCM bad or because it is seeing misfire. I figure the PCM only doing 1.5ms pulse to #3 slows down crank causing misfire? What you guys think?
The monitors show constant miss at idle 700 800 RPM then 1200 miss goes away until around 2300 comes back. I just do not know why injector on time is 1 mS less on misfire #3 off idle they even up. Adding propane to intake also evens up injector on time at idle. It seems to be lean misfire on one cylinder but PCM controls on time so is it doing it because of misfire? I clear code and still no change. Bad PCM weak driver? I Pico Scoped it and confirm on time compared to Hyundai Scanner data. I have asked everyone I can no one knows?
I did take a Cam Crank wave form compared to known good car exhaust slightly off. I bought WPS did a running compression on exhaust section shows 2 to 3 pulses on good cylinder shows 4 to 5 so I was thinking same thing cam has retarded from CVVT. I did one on same type of car were pin broke and cam shifted but was more obvious. I did take cover off did not see no damage oil covered all equal. One thing I did do was take off intake to see if runner flap on 3 might have separated but all 4 good and tight. So I put new seals on intake I did see slight out of position seal on 3 but very little reinstall manifold no misfire drove 15 miles would check thru my work day all good. The next day i sent out to our airport location for rental next morning CEL came on they send back to my location misfire 3 again. might have to tare down inspect cam to crank phaser alignment. But why only 3 misfire if slightly off?
I had a Ford with a similar misfire and VVT fault codes. Compression on cylinders 1 and 2 was 10% different to 3 and 4. It ended up being worn shims on 1 and 2. So it's possible for cam timing to be right but valve clearances to be causing the issue.
Getting involved in discussions because I have a lot to learn still.
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