P0302 - Misfire Cylinder 2: need help troubleshooting

[DesertRat]

07 Tahoe w/ 5.3 purchased used a few months ago. CEL comes on when idling for roughly 5 mins or so. I've checked the code and every time it's P0302. After purchasing the vehicle I changed plugs and wires, and changed oil. After CEL came on I verified wire and plug were installed correctly on cylinder 2. This weekend I checked voltage to the coil, but didn't have an HEI spark tester so I swapped #2 coil with #4 coil to see if the problem followed the coil. Yesterday I intentionally let truck idle to trigger the CEL, which it did come on. I checked the code, still P0302.

CEL came on before spark plug change as well. Gas is routinely 91.

At this point I'm ready to take it to dealership or qualified mechanic to diagnose since I'm not sure what else to do. What else can I check before going that route?

I want to run fuel system cleaner through it just to see what happens.

 

[Rocket Man]

Do you have DOD/AFM ?

 

[Doubeleive]

maybe a bad injector, maybe it has a intake leak?, I would test for a intake leak and maybe swap injectors

 

[Phantom911]

Hi, I had the same issue on my 2007 Yukon with 137K mixed miles atI changed the plug and coil indicated by the code and it continued to happen. I took it to the dealer and they said that it was related to DOD. They could fix it for $3500. I didn't do it and it's been about a year or so since the diagnosis. It doesn't idle smoothly but there are no problems at speed. The dealer did say to change oil more frequently to keep it from getting worse, something about the oil passages used in the DOD/Cylinder deactivation. I'll probably put in some kind of oil treatment on the next change. Good luck.


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[sumo]

You already swapped plugs and coil and it remains. Next I’d swap injectors to see if it follows. But the best thing would be to do a compression test.

 

[DesertRat]

Do you have DOD/AFM ?

Yes.

maybe a bad injector, maybe it has a intake leak?, I would test for a intake leak and maybe swap injectors

You already swapped plugs and coil and it remains. Next I’d swap injectors to see if it follows. But the best thing would be to do a compression test.

I'm going to swap the injector to see if changes anything. Over the weekend I pulled the connector and the change was minimal at idle. Thanks for the input, I'll check compression and for leaks in a couple weeks. Given the history of the vehicle those would be good to do anyway.

 

[swathdiver]

Who do you know with a Tech2 Monte?

 

[DesertRat]

Who do you know with a Tech2 Monte?

No one that I'm aware, but I'll ask around. Is there something specific a tech2 would do for me in this situation? I'm a newb when it comes to GM vehicles, this is the first I've owned. I plan to keep it for a while so I may just need to pick one up.

 

[swathdiver]

No one that I'm aware, but I'll ask around. Is there something specific a tech2 would do for me in this situation? I'm a newb when it comes to GM vehicles, this is the first I've owned. I plan to keep it for a while so I may just need to pick one up.

There's lots it can in this situation. First of all, it can run a test on your AFM system. It can see when and how you're misfiring. It can turn the injectors on and off also for testing. It is absolutely essential to have one to successfully work on these trucks without throwing parts at them.

 

[DesertRat]

There's lots it can in this situation. First of all, it can run a test on your AFM system. It can see when and how you're misfiring. It can turn the injectors on and off also for testing. It is absolutely essential to have one to successfully work on these trucks without throwing parts at them.

Any suggestions on where to pick one up from? I've seen them on ebay and obd2eshop.com but am still trying to figure out if there are differences. More to the point, I found one on obd2eshop.com for $240 (SP23-1) which ends up being $300 with shipping. It doesn't come with a hard case and it's hard to tell how it compares because the language attempting to clarify difference between items on the website is vague at best. Differences cited on the website are carton box vs hard case or the same but cheaper (lol).

EDIT: additional info added.

 

[ecordell]

Try your O2 sensor underneath the passenger seat.

 

[07 black beauty]

Do or have a compression check done on cylinders. With a 5.3 that has AFM\DOD, most likely it will be a lifter issue.
and if it is related to AFM and you have it repaired, please get the AFM crap deleted or at least disabled.

 

[DesertRat]

Do or have a compression check done on cylinders. With a 5.3 that has AFM\DOD, most likely it will be a lifter issue.
and if it is related to AFM and you have it repaired, please get the AFM crap deleted or at least disabled.

checked compression on the front four cylinders, all were around 170/180. I'm going to check wires next. I disconnected the #2 injector wire and no noticeable change. Just have to take the time to chase the wires and check continuity

 

[DesertRat]

maybe a bad injector, maybe it has a intake leak?, I would test for a intake leak and maybe swap injectors

This looks like it might be the winning answer. Last weekend I replaced the intake and valve cover gaskets, and I noticed an immediate difference at idle and overall performance. Gasket at cylinder #2 was noticeably not sealed correctly. Even after idling for prolonged periods of time this week, the CEL did not come back on. It's only been a week though, so it's not been thoroughly tested.

After rereading my first post, I should clarify that in most instances the CEL came on after idling for several minutes.