Jkborow

Ronjenx I see you posted this check list many times on this site. Do you have insight into this problem. I'm tr ing to avoid tare down of my engine for a stumble at idle with a ce light. I could see the test procedure would prove vital for a random missfire.

But mine is isolated to #2 with all basic parameters in spec. This is a out of the ordinary issue. And that's why I'm asking for help. Trying to avoid hours of diagnosis.

ronjenx

The list I posted appears in each of the individual cylinder misfire charts, as well as the chart for multiple cylinder misfire. Misfire is not necessarily a misfire. It's anything that causes the crankshaft to momentarily slow down. That's why the list is so long.

All I can say is, grind your way through the list, starting with the easy stuff. You've done some of it already.

07 Rescue Green

I'm having the same issue but with Cyl #1. My guy is certain it's the injector so Monday it's getting one. When you pull the plug, it's fouled. If you clean it up and put it back in the Check eng. light goes out but comes back within a few days. Hopefully this'll fix it.

Spytec128

I currently have a misfire on #2 and it is my intake gasket leaking antifreeze into that cylinder. The coolant crossover channel runs right next to the #2 cylinder. Mine will misfire until it cleans up the cylinder and then runs fine. Usually takes about 20-30 seconds.

ronjenx

Did a cylinder leakage test reveal that? If not, how did you come to that conclusion?

SP3CTRE

Did you ever resolve this issue, and what did it finally end up being?

Winyah

It would be nice to group the list of potential causes by items that cause multiple codes and the ones that would only cause 1 cylinder code. I have P0306 only- it's intermittent, happens when engine is under high load (like climbing a hill), Im am getting back fires. So which ones should I rule out immediately?

TheTerminator

I'm sure you can google for these things. It's common for most gas engines.

It's impossible to tell over the internet what is the cause of your misfires without diagnosing the problem. In order to diagnose the problem you first of all need a good understanding of how combustion happens in a gasoline engine. Any time the combustion is off, you are going to get a misfire. From there you gotta look at every single component/system that affects the combustion. To look at it you need a scan tool, which can be bought for $100 or less. You really want one that can graph PID's, but being able to see PID's like short/long fuel trims in real time is very helpful too. A scan tool will not show you everything, so for other things you need an oscilloscope, which is basically a "scan" tool for electrical signal, allowing you to look into any wire and see what is happening over time (on a graph).

Or you can simply do it the dumb way and start replacing every single component until you hit the problem. But the list can be very long, as even alternator and battery can cause misfires at times. And if it's a wiring problem, you will replace everything and still be at square 1. So that's not the recommended way of tackling misfires.

Just from your description of the misfire, I would start looking at fuel delivery and ignition as they seem to be struggling under load. So look at fuel pressure and injectors (specifically injector #6) under load. Look at your ignition coil, wires, and plugs. Look at your crank/cam shaft sensors.

ronjenx

Let's all remember that a misfire code doesn't necessarily mean an actual misfire has occurred.
This is made clear by all the people who have replaced ignition and injection parts only to have the "misfire" persist.

Anything that causes the crankshaft to slow when the computer expects to see it maintain or gain speed will throw a misfire code.
Also, if the computer throws a code for a particular cylinder, it will eventually shut down injection for that cylinder.

jtphoto JK

Misfire under load is usually a Bad sparkplug or plug wire. I suggest changing all the spark plugs and don't try and go fancy. The 3.8 likes the factory Champion platinum plugs. Anything else will likely cause you more grief... If factor original plug wires are still on there, change them as well.