Hello this is the first time I post here and I like to ask you guys if anyone expirinced the same or similar issue in the past.I am having a p0304 code missife for the past few months on my 2008 Tucson 2L FWD 190.000 klm.I bought in may 2020.I have changed spark plugs and cables.Did a compression test in the cylinder Wich showed good.Swap the coil pack to see if the code transfer to another cylinder (Wich it didn’t).Used 2 times a very good fuel injector cleaner(bg44k) and the check engine light still keeps giving me the same code.The car since the beginning is not stalls or hesitate.My mechanic can’t find it and we don’t won’t to start changing every part that might cause it(too expensive).I even tried the Hyundai dealership 2 days ago and the couldn’t find a missfire or any data(maybe because my mechanic was clearing the code after every check).both the dealership and my mechanic said it is not a vacuum leak because it would show another code not p0304.Any ideas what might cause it or what to check? could it be electrical issue ? P.s. I am replacing my vvt solenoid this Monday along with oil change .Can the vvt solenoid (sensor to control oil in the engine) be causing missfire?
Try swapping the fuel injector for #4 to another cylinder and see if it follows the injector.
It might be a sticking valve in that cylinder caused by a bad valvespring or gummed up valves. You won’t find that on a compression test. Remove the valvecover and take a good look at the valvesprings for #4.
Thanks for the info.How easy it is to check the springs on a 4 cylinder engine?
Pretty easy to check valvesprings. Remove valve cover and look for broken coils. Take a pry bar or screwdriver and compress the spring just a little bit. If takes less force than its neighbor on #3, that may be the one. Replacing a broken spring can be easy or hard depending on the engine. Not sure which yours may be.
Start with the fuel injecter swap, then check springs.
Thanks a lot.Probably I ll have my mechanic swap the fuel injectors on Monday when I ll do my oil change and if that doesn’t move the error to another cylinder I ll try the springs my self
If you are using a mechanic for oil changes and injector swap, I’d suggest maybe you don’t have the skills to check valvesprings. No offense intended, but it is far more difficult than an injector swap.
No offense taken.For the oil change I use a mechanic because I don’t have the space and time and once he is a good man also he won’t charge me for the injector swap.As far as the springs if I decide to go there I might ask him if he has time and what will cost me for him to check them and if it requires a lot of time( so that means labour) I ll do some search see how difficult it is and try my own.I mean I know everything in a 2L 4 cylinder dohc engine it’s easier compare to other types of engines
Define what is meant by “good” on the compression test. People come onto this forum all the time with claims of good compression when the reality is that the number provided is not good at all.
Good should be 180 and up. A 150 is half worn out and it’s nearing the end at 130 and down.
Sorry you are right.i believe it was between 170-180 something it was a while ago and unfortunately I didn’t mark it down
Hope for a dirty injector. You could have a failing valve lifter in #4, which is a bigger job.
I haven’t swaped injectors yet but I am worried it’s not that because I have used the bg44k Wich I read and heard the best from among other cleaners.So if it was a dirty one wouldn’t 2 cans of that do the job already?So my understanding is so far if I ever buy a used car again and read with the obd2 a missfire just walk away … because it’s one of the codes it can be caused by million things 
Did some research and it’s easy to change/check the fuel injectors on a 4 cylinder engine.One guy gave a tip to release the pressure from the line before I take them out.And if I am about to replace it(better be all four of them) dip the new ones in gas before I put them on so the seals won’t leak.Any other tips or something I would pay attention when removing/swaping/changing the injectors on my dohc engine?Also any tips or standard signs that I will see on a bad /clogged injector when I ll check it?
You likely won’t see anything on a bad or dirty injector. Yes, replacing the set would not be a bad thing on a car that old.
You should probably have new O-rings to install on the swap injectors as the old ones are may tear when you remove them. You should lube the O-rings with a little motor oil or trans fluid, not gas, before installing them.
thanks man i ll see what i can do and keep you posted
Στις Σάβ, 5 Δεκ 2020 στις 8:58 π.μ., ο/η Mustangman via Car Talk Community <cartalk@discoursemail.com> έγραψε:
Hey.i tried the trick Wich you put one end of a long screwdriver at the injector and the other end to your ear to hear if it’s firing consistently.They all 4 sounded good.Now if I just swap the cable plugs from the injectors e.g 4th with 3rd would it be enough to show me p0303 instead of p0304 if it is a clogged or bad one ?or I have to swap the actual injector too?
The injectors open sequentially to match that cylinder’s motion so No, you can’t just swap connections, you have to physically swap the injectors. You are hearing the pintle in the injector move when hit with voltage, that’s good, but it doesn’t tell you that the proper amount of fuel is flowing.
Thanks man good stuff.But like you mentioned before I ll better have spare o-rings to replace them because once I ll start pop them out the o-rings are going bad right?
Yup… the old rings will likely stick quite a bit and can tear upon removal… or they will so flat-spotted from being in the engine for so long, they won’t seal.
I ll do an oil change and vvt sensor replacement along next week.Weird thing that the check engine light turned off yesterday by itself and came back on today.Is that telling you anything? Like it’s a minor issue or a sensor? If it is a clogged injector can it missife periodically?
Yes, indeed it can.