cold start misfire

Good morning.

Carbon is the biggest issue. there gets to be a build up on the face of the intake valves. When carbon is cold, it will absorb the fuel mixture to the carbon. when it gets hot, the fuel flow will not be absorbed and the misfire will go away.

Toyota had this issue for years for the same issue.

Have you tried top engine cleaner on the intake system?

Roy

yes I did bg, and crc is it possible that the temperature sensor is giving a false signal to the computer or perhaps there is an update on the computer?

No, it is not a software issue.
if the temperature sensor was bad it would code.

GM top engine cleaner is the only one we use. it works the best.

Roy

Roy, Thank you so much. I will hunt it down and give it a try, Charlie

You are welcome, keep us updated.

Roy

Roy, brought it into the shop 5mm. of carbon, they told me to bring it to Hyundai there ts an update 12-fl-007 which must be performed before repair. They told me the update may fix the issue if not, valves need to be cleaned removing the intake soaking the valves in solution. Does that sound correct, they also told me regular induction will only remove 1/2 to 1 mm of carbon. Thank you so much, Charlie PS: if I continue to use tier one gas, more frequent oil changes, and induction cleaning would that remedy the situation.

Yes, it sounds correct.

you can try better fuel and oil changes but it will take a long time to get any results.

I would have the top engine cleaning gone several times to see if that will do it before considering removing the cylinder head.

Roy

I originally meant removing the intake manifold not the heads to soak the valves in solution. Well, I went to Hyundai today they said there was no update on the computer but I had them do that GDI service which was expensive comparing it to me doing it myself through the throttle body. They went through the fuel rail, and they were quite thorough. They suggested as you said more frequent cleaning, I can do that myself was just wondering how often can I do that going through the throttle body. Did not want to cause harm doing it to frequent. Thanks again, Charlie

I would do it every couple of months.

I shall. Thanks again.

You are very welcome.

Roy

Still trying to figure out the problem, had it walnut blasted for carbon no change. It has something to do with operating temperature with the ECM. I know the coolant sensor has multiple purpose, if that is the problem I will be kicking myself after spending $2,000.00 on it so far. A few other posts had the same problem and the remedy was the coolant sensor not setting off a code, really strange.

The coolant sensor controls fuel mapping according to engine temperature. If it was running rich or lean from he sensor, it would set off a O2 sensor code.

I also controls the temperature gauge on the dash.

Roy

Roy, An update on the Genesis, the shop that did the walnut blasting said the good news is no carbon. The bad news the carbon did damage to number six valve seats recommend valve job $2,300.00. If that is the problem for what I paid for diagnostics, valve cleaning, walnut blasting I could have paid for a valve job. Roy, after all of this expense the car runs exactly the same. Aside from torching the car, what do you suggest? I have driven the car in this same condition for about a year no change at all.

Did he do a compression test in number six cylinder?

Roy

They said compression was fine, something about leak down and recommended a valve job.

If there was damage to the valve seat, the first thing that would be affected is the compression.

You have been driving it all this time and you can continue to drive but at some point, it will have to be addressed.

Roy

Interesting, it needs a valve job yet the compression is good in cylinder number six? They told me when the car warmed up because of the carbon build up the valve seated and ran smoother. Now with all the carbon gone if it does exactly the same thing they are not being truthful. They did a manual cleaning with chemicals taking off the intake, then when it ran the same they did it over again with a walnut blaster that they said they ordered in. I told them cannot afford a valve job, they said we will put it together and you can pick it up on Monday. I am curious to see what they are going to attempt to charge with the walnut blasting. I wish I can just find and honest repair shop. Thanks Roy, God bless you.

I understand. Let me know what they say.


Roy

Will do, thanks.

You are welcome, glad to help.

Hello Roy. They showed me pictures all the carbon is gone except on the bottom of number six valve compression is fine. They said there were chunks of carbon on the bottom of the valve which is not accessible through cleaning unless the head is removed. It runs much better especially after it reaches operating temperature. It is still rough until it warms up about ten minutes. I noticed it is getting a lot better gas mileage. Now they mentioned possible valve guide or just a chunk of carbon being the culprit. I am thinking for right now to watch it closely change oil regularly, tier one gas. If you were in the proximity I would just give it to you to fix. Have a blessed day, Charlie

I agree, I would drive it and see if it improves. Use premium fuel in it to increase heat to help get rid of the carbon.

Roy

Hello Roy. Well I have been driving it and the engine light came on P0420, it is the left bank quite sure it is the catalytic converter. There is also a strong carbon smell inside the vehicle. Mechanic told me to put a gallon of solvent in the gas tank to clear it up a little reluctant to do so. Anyway, I work at Toyota and one of the mechanics is going to remove the heads and install when machine work is done. A friend of mine owns a machine shop told him about number six valve seat said they will go through it thoroughly. Then through rockauto.com they have a company that reproduces the converter at a fraction of the cost you just send them the old converter. I have not started the process yet does it sound like the only solution. Thanks again, Charlie

Hello there. Yes it is the catalytic converter. There is nothing that will clean it out. The precious metals are worn out and need to be replaced.

Roy