Stewart Rife

So I just did my head Gasket in my 02 GT 2V but afterwards it ran great no hesitation in driving idles great. But I'm getting a code for p0306 and another code p0316 (misfire found within first 1000 rotations) the car itself doesn't have any skips or chugs when idling or whilst driving.

Here's the other thing the code only comes up when the motor is hot, if it turn it off and restart it when it's up to operating temperature it sets the code. When it's cold there's no code. I've driven from cold start to all the way warm 30+ min no code.. As soon as I turn it off and restart solid code. Another odd thing is it's not flashing like I've seen misfires do as well it stays solid on the dash. Now​ I do know the exhaust had quite a bit of water from a blown head gasket could that cause a catalytic converter to go out?

I've read that sometimes this is an issue.and before we ask "have you checked for spark, fuel, compression?" Yes all three check out just fine. They are operating normally. In fact I checked all cylinders for all three.

Camster

I'm certainly no expert,hopefully one will come along shortly,but when I hear about a lot of antifreeze going down the exhaust,I'm thinking that an O2 sensor might have been damaged.

Stewart Rife

Yes that could be an issue didn't really think about it. I have a second X pipe on my other GT just haven't had the time to swap it out. My thoughts exactly though. I feel like it ruined the Cats because of the antifreeze.

Thanks man

WJL

FWIW, anti freeze down the pipe will not or shouldn't throw a specific cylinder code p0306, indicating a miss in cylinder #6

the o2 sensor has no way to detect which cylinder is missing, it really only control fuel mixture.

Being you just put it back together:

Check all the spark pug wells for antifreeze, blow them out with compressed air if possible

Make sure fuel injector and COP connectors are on tight

Worst case pull plug #6 and take a look at it, some times it will show something (burning anti-freeze/oil)

Good luck

Stewart Rife

I have blown out the cylinders with air they are all dry and free of debris. I'll double check the injectors when I'm home, I was going to use a tester and make sure I'm still getting power to them. I've read before that when a cat goes out it will rarely but sometimes mimic a misfire. I will know for sure soon I'll be swapping out the mid pipe as well as the EGR valve. The EGR might be stuck open. What's the COP connector​? Is that the ignition coils?

WJL

In my experience if the catalytic converter melts down that's exactly what it does melts down. a clogged converter can turn Cherry RED hot

The up stream or down stream o2 sensor has no ability to detect a miss fire and if your not getting any o2 codes, more than likely that's not the problem.

Replacement of good oxygen sensors is one of the most common mistakes that both seasoned auto repair mechanics and do it yourself driveway mechanics will make when tackling o2 diagnostic codes.

Yes COP Coil on plug, again pull the spark plug and see what it looks like. If the EGR is stuck open although it can cause a miss you will have idle issues as well and i would expect it to throw an EGR code.

Keep looking if you didn't have this problem before replacing the head gasket, it got to be something that was worked on or moved, which side did you replace the head gasket on, did you remove the cam sensor, some time a malfunctioning cam sensor will do some weird stuff, with that being said don't run out and buy a cam sensor they can be checked.

Good luck

Derf00

Try swapping the #6 plug and COP with one from another cylinder, if the misfire follows the plug/COP, then one or both are the problem. Blinking CEL is usually a severe misfire. You may just be getting an occasional voltage leak so it just spits the code out but doesn't blink.

Might also want to check out the injector.

The other thing (and you're not going to like this one), is the valves aren't seating properly in the #6 cylinder. Did you inspect the head or have the heads cleaned up at all before reinstalling them?

Anecdotal experience here. 07 Chevy Cobalt with 2.2L Ecotec motor. Ecotecs from 06-09 are notorious for getting misfire codes due to improper valve seating. It's because the aluminum head is made using a lost-foam cast aluminum method. If you look at the heads you'll note in some areas they literally look like metal versions of Styrofoam. They have a tendancy to either warp or collect carbon around the valves in such a way that it eventually causes the valve to have problems sealing all the way. What you end up with is a misfire code(s) like the ones you are talking about. It also won't give much in the way of driveability problems either.

A compression test will come out Ok in most cases but a Leak-down should identify it.

WJL

Swapping the coil and plug is the best idea I've read in this post, if the code follows the COP then there you go.

if not could be a leaking head gasket, that leaks after it warms up check the exhaust upon start up see if its blowing white smoke. A leak down is also a good idea but it wont tell you if its a head gasket, valve or rings.

Again did you have this problem before replacing the gasket?

Z28KLR

I would also check down the list of possible causes for your P0316 code, which is often a faulty crankshaft position sensor signal. Here's some more info....

https://www.obd-codes.com/p0316

And as stated above, definitely swap out the coil from #6, reset the CEL and next time it pops up see if the dtc followed the coil or stayed at #6.

dawson1112

Or the misfire with in the first 1000 miles could very well just be because you just did the head gaskets and it was missing a little till it buned the gunk out of the cylinders from having it tore down. Clear the codes,,, if its running good and not flashing drive it.