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Discussion Starter #1 (Edited)
Any Kia techs?

My son bought a nice little 2007 Kia Rio a couple weeks ago. It has a misfire problem that we are having trouble diagnosing the cause. Random misfire code and cyl 3 misfire code. The misfiring happens at lower rpms but runs smooth at lower rpms at times. Runs great above 1500. Seems to be a little worse when engine is cold. This is a 1.6 engine iirc.

When he bought it, it had 3 coils that weren't originally for this car. Replaced all four coils and have replaced injector on number 3 cyl. We've moved plugs and coils around and number 3 is still dead at times.

Any ideas? Possible faulty crank or cam position sensor? I've googled it a good bit but haven't really come up with anything.
 

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have you done a compression test? could also be wiring to the coil but unlikely if it runs good at higher rpm. How did the plugs look, did you just move them around or replace them? Any corrosion or carbon tracking on the porcelain
 

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Discussion Starter #3
have you done a compression test? could also be wiring to the coil but unlikely if it runs good at higher rpm. How did the plugs look, did you just move them around or replace them? Any corrosion or carbon tracking on the porcelain
Haven't had time to check compression yet but was gonna check that next chance I had. Don't think he's changed the plugs out yet, think he just moved them when he pulled them out to look at them. Will replace plugs when we do the compression test.
 

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tight valve lash, chunk of carbon on the valve, small piece of exhaust valve chipped of......compression and leak down test is needed.

Now THIS will cause more than a slight misfire.....

 

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Discussion Starter #5 (Edited)
tight valve lash, chunk of carbon on the valve, small piece of exhaust valve chipped of......compression and leak down test is needed.
Makes sense with the number 3 cylinder being dead mostly. Would this make it throw the random misfire code also?
 

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Makes sense with the number 3 cylinder being dead mostly. Would this make it throw the random misfire code also?
P0300 and P303 or any missfire codes will often set as a pair, part of the obd2 implementation specifications.

I would pump the motor with a good compression gauge, I have seen a few of those engines eat headgaskets.
 

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Discussion Starter #7
Ok thanks for the info guys. Will do the compression test and see what we come up with.
 

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Discussion Starter #9
Does the misfire go away with RPM ( driving it ) ?
Check the intake gasket and inj. for vacuum leak .
Yes. Runs great above around 1500 rpms. Out on the highway you wouldn't know it had problem.
 

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Discussion Starter #12
I did spray and check for leaks a little but didn't have a lot of time that afternoon. Idle air valve didn't have a gasket and was leaking pretty bad. Thought that would have probably fixed it but it didn't. I'll do more checking for vacuum leaks.
 

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If this is a hyundia motor which is likely is the shared mitsubishi hyundai chrysler engine, more then likely it may have rotted injector orings at the manifold, but first, do a compression test.
 

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Discussion Starter #14
If this is a hyundia motor which is likely is the shared mitsubishi hyundai chrysler engine, more then likely it may have rotted injector orings at the manifold, but first, do a compression test.
Possibly. In some of my google searches I was coming up with hits on Hyundai and I was thinking Mazda but may have been Mitsubishi. I just know it's a 1.6.
 

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Discussion Starter #17 (Edited)
Just wanted to give a update for the guys that replied with help in this thread. Those of you that mentioned the compression check were right on the money. Number three cylinder didn't have any compression to speak of. Son pulled the head and it looked like a ground electrode had broken off of a spark plug. Piston had some minor spots but cylinder wall was not hurt. He took head to shop and it needed both intake valves. Waiting on head now.

Sorry about being so late replying with what he found, I had forgotten about this thread. I got sick with the sinus crud that had been going around here and right after I got over that I took a tumble from about 10 foot up a ladder and broke my wrist in multiple places. Had surgery to repair that this past Tuesday.
 

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I have lost 5 weeks of working since mid December due to sinus crud.

Hyundai/Kia filled the spot when Honda decided to be like Buick and leave the small car market behind.
 

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This sounded a lot like a VVT-related issue that we just went through on a Mazda 2.3, and is almost a universal issue with higher-mileage Ford 3-valve V8's, but apparently not. Glad you and your son found the problem.

2 weeks into the sinus crud. 5 weeks? Lovely. :(
 

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This sounded a lot like a VVT-related issue that we just went through on a Mazda 2.3, and is almost a universal issue with higher-mileage Ford 3-valve V8's, but apparently not. Glad you and your son found the problem.

2 weeks into the sinus crud. 5 weeks? Lovely. :(
Three weeks the first time, wasn't so busy. The two weeks of crud in middle of Feb. really put me behind. No time to work on my own junk...
 
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