P0303

Dadillac · Sep 19, 2020

My son has a 2012 Hyundai Veloster that has the NA 1.6 engine. Running bad and has a cylinder 3 misfire. Change the plugs no change. Checked for spark and it has spark. So That lead me to believe that it is not getting fuel in cylinder 3. So I changed the injector and still no change. I changed the injector harness and again no change. So now I think that the ECM may be bad. Before I go down that road does anyone have any other ideas. Thanks

Don

FordMan59 · Sep 19, 2020

Just because it has spark it may be weak and maybe a bad coil. I'm not familiar with this model but, if it has individual coils for each cylinder like most later models I'd move that coil to another plug, clear the codes and see if the misfire follows that coil.

fd1430 · Sep 19, 2020

Dadillac said:
My son has a 2012 Hyundai Veloster that has the NA 1.6 engine. Running bad and has a cylinder 3 misfire. Change the plugs no change. Checked for spark and it has spark. So That lead me to believe that it is not getting fuel in cylinder 3. So I changed the injector and still no change. I changed the injector harness and again no change. So now I think that the ECM may be bad. Before I go down that road does anyone have any other ideas. Thanks

Don

Did you check compression on that cylinder?

mattd · Sep 19, 2020

Swap coils to adjacent cylinder and see if misfire follows. If it doesn’t I would check compression.

Rand · Sep 19, 2020

maybe valves really bad gdi deposits?

need more testing.. should be able to diagnose without more parts.. might need a tool or 2.

slacktide_bitog · Sep 19, 2020

mattd said:
Swap coils to adjacent cylinder and see if misfire follows. If it doesn’t I would check compression.

This.

It's by far the easiest thing to do on a coil-on-plug car to diagnose a misfire. The first thing I'd do

wpod · Sep 19, 2020

Before changing parts diagnose the problem.

Trav · Sep 20, 2020

Dadillac said:
My son has a 2012 Hyundai Veloster that has the NA 1.6 engine. Running bad and has a cylinder 3 misfire. Change the plugs no change. Checked for spark and it has spark. So That lead me to believe that it is not getting fuel in cylinder 3. So I changed the injector and still no change. I changed the injector harness and again no change. So now I think that the ECM may be bad. Before I go down that road does anyone have any other ideas. Thanks

Don

Everything has pretty much been covered but if moving the coil doesnt identify the culprit I would get a Noid light to make sure you have impulses from the injector driver circuit of the ECM.
Swapping the coils and using the Noid light is the easiest thing to do before digging deeper, eg compression, leak down, deposits, etc.

This is a set, they are sold individually everywhere.

Amazon.com: OTC (3054E) Noid Lite/IAC Test Kit : Automotive

Buy OTC (3054E) Noid Lite/IAC Test Kit: Electrical System Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Dadillac · Sep 20, 2020

So let me add to my initial post. Coils were swapped without the misfire following the coil. Compression test was done by pulling plugs and testing without a gauge. Even partial compression would have the cylinder firing somewhat. With the engine running when I pull the coil plug for cylinder three there is zero change in how the engine runs. So I am 100% dead on three. I bought the replacement computer and will hope it works out. Either way this car is moving on by next weekend. Son is buying a new car and we just want it running so it can be traded in. If the new computer doesn't fix it he will sell it as mechanics special for whatever he can get for it

Don

terry274 · Sep 20, 2020

Dadillac said:
Compression test was done by pulling plugs and testing without a gauge.
Don

What does this mean?

mk378 · Sep 20, 2020

Cylinder drop test, has nothing to do with compression.

Nukeman7 · Sep 20, 2020

Trav said:
Everything has pretty much been covered but if moving the coil doesnt identify the culprit I would get a Noid light to make sure you have impulses from the injector driver circuit of the ECM.
Swapping the coils and using the Noid light is the easiest thing to do before digging deeper, eg compression, leak down, deposits, etc.

This is a set, they are sold individually everywhere.

Amazon.com: OTC (3054E) Noid Lite/IAC Test Kit : Automotive

Buy OTC (3054E) Noid Lite/IAC Test Kit: Electrical System Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Trav is 100% on target here. Given the conditions listed and inconclusive test results, I would suspect that you have a broken wire/connector in the harness feeding the cylinder #3 coil. That happened to me on a '03 Odyssey van during a 600 mile road trip in 2018. You can even get a loaner set of Noid lights free from Autozone with a refundable deposit.

P0303

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