# P0303



## Robby (Mar 1, 2013)

vigil14 said:


> So I've been having misfire problems since it got really cold here. I always let my car warm up before I drive it and I keep up on all my maintenance. I have brand new spark plugs in my car, and I just replaced the ignition coil yesterday because the old one was corroded.
> 
> I thought it was misfiring because the coil was really corroded, but when I replaced it, it still happened. Its better then it was, but it still misfires at idle and just a little when I drive it.
> 
> Me and my friend think it might be something with the valve train, so I put some seafoam in the gas in case some carbon built up. Any opinions or experiences are greatly appreciated.


Few minor details needed......model year of car......I'll assume it is a Cruze.
What engine and how many miles are on it?

Currently we don't know if you are servicing a car or a lawn mower, heh heh.

Rob


----------



## vigil14 (Feb 24, 2013)

2012 Cruze Lt and it's not to far from a lawn mower


----------



## Robby (Mar 1, 2013)

vigil14 said:


> 2012 Cruze Lt and it's not to far from a lawn mower


I ask the miles to help me determine if there will be a powertrain coverage available to you.
Although this code can be a result of a coil problem as you found, the misfire code can be set by anything electrical or mechanical.....for example, a localized vacuum leak can set a misfire code.

For starters, a compression test is the first step.....you need to verify the engine is sound mechanically before looking at a potental ignition problem.
If one cylinder is lower than the rest by about 20% or more, a cylinder leakage test is called for.....this to determine if there is a sealing problem caused by rings or one or more valves not sealing.

Once you have determined the engine is mechanically sound, thats when you begin, first by inspection, then by test to see if it is a ignition problem.

These steps are the normal diagnostic process a mechanic follows to avoid wasting time and needless part replacement expense.

If your vehicle has less than 100k miles and, since it is a 12, we can assume it is less than five years old, and you are at all uncomfortable with the mechanical tests I mentioned, then let a dealer chase the problem.

The car is not known for any signifacant mechanical concerns and there are some very high mileage posters on the forum.

Rob


----------



## vigil14 (Feb 24, 2013)

All that's noted thanks for the reply. The reason why I'm posting about this is to see if any one has had the same problem.


----------



## BowtieGuy (Jan 4, 2013)

- How many miles do you have?
- What kind of spark plugs did you just put in (Stock, brand/model?)
- What are your plug gaps at currently?
- Do you have any rips in your spark plug boots or crack in the plastic on the coil? Either will give you a misfire.
- Have you checked the springs inside the boots to make sure they are not stuck up inside the boots or caught on the sides of the boot instead of contacting the spark plug? This is a common problem with the springs inside the boots.

That's about all I can think of at the moment.


----------



## vigil14 (Feb 24, 2013)

I checked everything. I pulled all the springs out and put a little di electric grease so they won't corode.


----------



## vigil14 (Feb 24, 2013)

My gaps are at .028 and I'm using the stock ngks also, and I have 70,000 miles


----------



## jstahliv (Apr 13, 2016)

So after fixing the negative battery cable ( previous one was loose) the car was fine for a few days. Yesterday when I started going (very cold), i got P015b (o2 sensor delayed response-lean to rich) and p0302 (cylinder 2 misfire detected). Is my O2 sensor going out and should be replaced?


----------



## jstahliv (Apr 13, 2016)

I had this problem. Here it turned out to be missing check valve on intake manifold (145 if you CALL carid.com to order) and PCV diaphragm in valve cover (70 bucks) replacing pcv hose just in case (40 bucks amazon) Refer to http://www.cruzetalk.com/forum/34-g...4-pcv-valve-cover-intake-manifold-issues.html for more info. *this is all after i did negetive battery cable, spark plugs gapped at .28 (irridium autolite xps) and ignition coil. Will update if i remember in the future.


----------

