Kia misfire


my friend has a 06 kia Rio with a 1.6L with 66k on it, it got a misfire on cyl 3 so we replaced the plugs, still missed but not as bad and the light only came on between 20mph and 50mph, but still missed the entire time, i thought maybe a bad coil so i swapped them around to see if wed get a miss in a diff cyl, no luck sill a miss on cyl 3, so coil is good, plugs are good. so im left to think the injector could be bad, but they were replaced by kia 2 months ago. any help is appreciated thanks

I’m not real familiar with the Kias but most vehicles like this use mechanical valve lifters. This means that valve lash should be inspected and adjusted regularly.
If not, it’s possible for a valve, or valves, to tighten up and prevent their closing. This in turn will burn the valve face and valve seat. This is most common with the exhaust valves.

Look in the owners manual, under the hood, or on the upper radiator support for the specifications sticker and see if there is a reference to valve lash. If there is, run a compression test. If cylinder 3 is down start expecting the worst; as in time for a complete valve job.

Didn’t Kia already have a 10 year/100,000 mile Powertrain Warranty by 2006? Or did that coverage begin in 2007?

If the car’s Powertrain Warranty is still in effect, I suggest that you allow a Kia dealership to do the diagnosis and necessary repairs, gratis.

I’m Not A Pro Mechanic, So Take This Advice Accordingly. I Believe This Kia Has CVVT (Constant Variable Valve Timing).

Are you getting a fault code for a misfire on cylinder #3 and is that the only code(s) you have retrieved ?

Since switching coils around didn’t help, maybe the problem is with the valve timing system, even the OCV (Oil Control Valve) component.

Perhaps the reason the new plugs helped a little is because the mis-fire fouled a plug or plugs a little.

A Kia TSB (Technical Service Bulletin) written for Kia technicians says that even using an aftermarket oil filter can affect oil flow rates and they say to make sure the filter is OE not aftermarket. The flow rate may affect the OCV and therefore the CVVT.

The bulletin goes into a lot of detail on how to test an OCV before finding it faulty and a candidate for replacement. I would not assume this part is bad on this particular Kia. More diagnosis is needed first. Throwing parts at it is not a good plan.

You say the “light came on” , but do you know if any diagnostic codes were set that could help ? I’d have somebody retrieve any codes and write them down exactly as indicated. Some auto parts (chain stores) will do this for free in their parking lot.

Related Diagnostic Trouble Codes:
Codes P0011, P0012, P0014, P0015, P0021 and P0022 relate to camshaft position and timing.
Codes P0016, and P0018 relate to crankshaft position correlation.
Code P0300 relates to Random / Multiple Cylinder Misfire Detected.

Maybe this would help narrow the problem down a bit. You are concentrating on the igniton part of a misfire.

Get any code(s) and post them here.

I’m beyond my level of expertise here, so maybe a pro will weigh in and bail me out.