2010 Tahoe P0304 misfire

[Glenn Thigpen]

Hi to all: I am a new member of the TahoeYukon forum and need some help.
One of my grandson's has a 2010 Tahoe 5.3 flex fuel with AFM. This past week the vehicle started running rough, the check engine light started flashing, and it popped a P0304 code.

First thing we did was to swap coil pack and spark plug wires between #2 and #4 cylinders and install a new spark plug in the #4 cylinder. The misfire remained and stayed on #4 cylinder.

We checked compression on #2, #4, and #6 cylinders. The compression on all three was within five pounds of each other. I am not sure how accurate my pressure gauge is because the sight glass is cracked, but the compression on #4 is pretty much the same as the good cylinders on either side.

We hooked a firing indicator between #4 spark plug wire and #4 plug. When starting the vehicle, the light will flash for a few seconds, maybe two or three, then go completely dead. We checked #2 cylinder and the indicator fired properly on that cylinder so it is pretty safe to assume that the tool is working properly.

With all that being said, it seems to me that the problem is either an intermittent wiring connection between the coil pack and the ECM or the ECM itself. The transistor that provides the switching ground in the ECM could be faulty and shutting down after it fires a few times. But I do not know. I have never seen a problem with the ECM causing a misfire on one cylinder before.

Are there any electrical gurus here who can give me a few pointers? I do not want to send my grandson on an expensive wild goose chase, i.e. replace and reprogram the ECM without some more definitive testing, but I do not know how to test the ECM for that type of problem. Any help would be greatly appreciated.

Glenn

 

[Kraig]

Do the same spark test you did in cylinders 2 and 4 on 6. 4 and 6 are AFM cylinders, #2 is not.

 

[Glenn Thigpen]

Do the same spark test you did in cylinders 2 and 4 on 6. 4 and 6 are AFM cylinders, #2 is not.

Just checked. #6 6=is firing properly also. Also diagnostic software does not report misfires on any other cylinders. Thanks.

Glenn

 

[Kraig]

Do a visual on the wiring to #4 coil and the coil pack connectors on the valve cover

 

[Glenn Thigpen]

Do a visual on the wiring to #4 coil and the coil pack connectors on the valve cover

I did the visual and saw no problems. Plugged it back in and the darn thing started firing. Evidently a bad/oxidized connection. But am still getting the misfire. Now I don't know what else to look for.

 

[Kraig]

When you say it started to fire, but still has the misfire, do you mean it still has the code, or it’s still running rough? How did the plug look when you changed it?

 

[Glenn Thigpen]

When you say it started to fire, but still has the misfire, do you mean it still has the code, or it’s still running rough? How did the plug look when you changed it?

It still has the code and is still running rough. I am pretty sick today and probably will not be able to do any more checks until tomorrow. The plug I replaced was not fouled but had some type of deposit on the electrode insulator. I could flake it off with my fingernail. It also looked "moist" as in probably raw gas. The plug from the number two cylinder had no such deposits and was dry.

 

[Kraig]

Alright I hope you feel better, but this probably won’t help: there’s a distinct possibility you’re looking at AFM lifter/bucket failure.

 

[Glenn Thigpen]

Alright I hope you feel better, but this probably won’t help: there’s a distinct possibility you’re looking at AFM lifter/bucket failure.

That is a possibility that has occurred to me after doing a bit of internet research. Thanks for your help.