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Misfire Frustration

3K views 11 replies 4 participants last post by  AUTOSPARK 
#1 ·
First a disclaimer... I'm OK around cars but not a mechanic by a long shot...

I have a 2002 Hyundai Elantra and initially had a check engine light come on and when I had it scanned it showed a P0303 misfire code, but the car still ran really well.

I checked the odometer and it just hit 106,000 and I realized it's been a while since I've had the plugs and wires replaced so I started with that hoping that would solve the problem but it didn't.

A friend suggested that I replace the coil pack, so I replaced it but that didn't fix it.

A relative checked and found that I had a bad air intake gasket and he said that could cause the problem too, so we replaced it and while we were at it also replaced the valve cover gasket and exhaust manifold gasket just to get those out of the way.

I continued driving the car and it progressively has gotten worse, and started throwing a P0302 code and a P0300 code.

I read online about the o2 sensors, so I decided to replace both the upstream and downstream sensors... still have the misfire.

Continuing to troubleshoot the issue I decided to replace the camshaft and crankshaft position sensors. Still a problem.

I replaced the MAP sensor, still a problem.

While looking at the scan tool I noticed my throttle was moving even though I wasn't moving it, so I replaced my throttle position sensor... scanned good, but still didn't fix my misfire issue.

Normally I would have taken the car in but I figured for the cost of labor I could have new parts... but I figured I would have solved the problem by now. Any help or suggestions is appreciated!
 
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#2 ·
You need to stop "hanging parts"... sound like you just compounding problem as you go.. half of your claimed parts replace will do nothing for selected cylinder misfire..
 
#5 ·
Has this thing been overheated ?? Radiator hoses at back of head all crusty with stains/cheeze on short 90* elbow hose.. low coolant or crack at front of upper radiator tank opposite of the upper radiator hose joint ?

Heat a 2.0L Elantra engine enough, it''ll twist the cylinder head,, remove radiator cap and start engine,, make sure it don't bubble or blow out coolant
 
#6 ·
Thank you for the advice/suggestions...

I Did a compression test on each cylinder and got 180, 180, 185, 180... I'm not sure if cylinder 3 coming up as 185 is an indicator of something or not but the little pamphlet that came with the test book said as long as none of them were off by more than 20%?

I'm not sure how to do the injector balance test? I have access to a fuel pressure tester but lost the (schrader ?) valve adapter, so I'm kind of stuck on doing this test at the moment.
 
#7 ·
Thank you for the advice/suggestions...

No overheating issues, but I did notice that the temp gauge inside the car wasn't working. But when I checked the coolant it was full.

Pretty much the car has run great up to this point, it does get a lot of short mileage driving though... usually about 10 miles or less each time it's out so I've tried to keep up with oil changes etc.
 
#8 ·
Update:

A mechanic friend came over and took at my car, we had initially planned to check the injectors as suggested here but before doing so he decided to just start from scratch start troubleshooting from the top.

He pulled the plug wire from the #3 cylinder and it didn't have any spark at all... he put a multi-meter on the lead and it showed juice although we're not sure how much it should register but either way we're pretty sure we have a bad coil pack.

When I initially changed out the coil pack I checked for spark and it was good, but the car very quickly threw the misfire code again, this time #2 & #3 which are together on the coil pack.

"sbr711" said I need to quit hanging parts (good answer lol) which is making me wonder, is this a common problem with parts? I mean what are the odds that a brand new coil pack would have the same problem or worse than my original part? Also is there something else up the line that might be causing it to go bad that I should take a look at? Thanks for your input!
 
#12 ·
I mean what are the odds that a brand new coil pack would have the same problem or worse than my original part?
The odds are pretty slim but it's not totally unheard off.

ds_meyer said:
Also is there something else up the line that might be causing it to go bad
Maybe the coil isn't bad. Perhaps it's the coil driver inside the PCM that's bad. I've come across that problem a few times on Hyundai. Or maybe it isn't an ignition misfire at all.

If you don't have the proper tools to do an injector balance test, it might be a good idea to try swapping the two outside fuel injectors with the two inner ones to see if the misfires follow the injectors to cylinder 1 & 4.
 
#9 ·
"which is making me wonder, is this a common problem with parts? "


Yes. I had a Chrysler 4cyl that would just go nuts when over 4K rpm. Code kept coming up with a bad cam sensor, which made sense. So I replace it with a top tier aftermarket sensor and it got even worse. Buddy that had spent a lot more time around Mopar than me said that was one sensor you had to stick with the OEM on. Changed to a Mopar sensor and bingo, no more problem.
 
#11 ·
OEM parts not come in a Hyundai-Kia box at the corner parts store...
 
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