changing misfires

HawkMTP · July 14, 2018

Hey guys I have a 2014 Silverado 5.3L. After a recent service at the dealer here in Hawaii my CEL came on. I took it back in it was a cylinder 7 misfire. The dealer replaced the wiring harness and the #7 coil pack. Brought the truck back home light came on again. Used a friends code reader and had a cylinder 5 misfire. last night replaced all the plugs and noticed the #5 wire came right off the plug when I removed the coil pack. Today truck is running rough and now I have another intermittent CEL between solid and flashing for a cylinder 4 misfire. Plugs looked fine but replaced them anyways. Anybody have any idea what is going on. This truck on has 65,000 miles on it and has never had any problems until after the service.

Supreme Pizza · July 15, 2018

That's a tough one. Hard to pinpoint it based on those symptoms. What services did they perform at the dealer, prior to this problem?

If I had those issues, I would start with plugs, wires, a bottle fuel injector cleaner, unplug the battery for 30 minutes, check the air filter, and maybe look around for vacuum leaks and disconnected hoses.

What island are you on? Oahu?

silveradosid · July 15, 2018

to get that many miss fire codes all of a sudden i would be checking the gas sound like you got a bad tank

Supreme Pizza · July 15, 2018

45 minutes ago, silveradosid said:

to get that many miss fire codes all of a sudden i would be checking the gas sound like you got a bad tank

Ya, I was thinking that too, but he was saying it started right after the dealer serviced it. Maybe got gas right after leaving the dealer? I guess you could throw some Heet in the tank to see if it helps. Sometimes gas stations add water to their fuel to increase the profit margin. This stuff would help:

Edited July 15, 2018 by starman8tdc

HawkMTP · July 17, 2018

So ended up changing the #4 coil pack and now I only get a misfire on #4 when starting clear the code and it goes away and truck runs fine. Could it be air? Maybe a PCM issue im at a loss.

Supreme Pizza · July 17, 2018

16 minutes ago, HawkMTP said:

So ended up changing the #4 coil pack and now I only get a misfire on #4 when starting clear the code and it goes away and truck runs fine. Could it be air? Maybe a PCM issue im at a loss.

Could you describe this more clearly? You clear the code while its running?

Edited July 17, 2018 by starman8tdc

TJay74 · July 17, 2018

The trucks have had some issues with bad injectors that cause issues at start up. What code are you getting?

HawkMTP · July 17, 2018

Still getting the P0304 code however went out this morning and started it to go to work. No code but still running a little rough at idle. Yes i cleared the code with the truck running

Crstfr · July 17, 2018

MAF dirty?

HawkMTP · July 20, 2018

MAF looks fine. People keep saying its dirty fuel or possibly an injector but i dont think an injector would manifest after two other cylinders misfired.