cshadows74

First time my truck has acted up since I got it and it gave me a doozy of a code to work with. Lol. My 2011 silverado 5.3 gave this code a couple days ago. I was driving at about 35 mph and something just like "snapped" and it turned off the stabilitrak and TC and check engine was on solid. (when I say snapped I mean it was instantly. I didn't hear anything actually break, but it was just like flipping a switch.) Got it home, changed #7 plug and coil pack. Old plug was definitely past due to be changed. Started it, it ran "better" but still gave code in very little time. Got another coil pack and plug. Started again, "better" than last time, and took twice as long to turn the other stuff off and give the code again. Tried yet another coil pack and it run almost normal for a couple minutes, then started getting worse, then turned off the traction control and stayed that way for a few minutes before it turned off the stabilitrak (that may be backwards, not sure which one turned off first) and the check engine light started flashing (not solid this time). Checked the code and much to my surprise (or sorrow) it's P0307. I've wiggled and checked all the hoses and wires I see. No clue when the plugs and wires and coils have ever been changed and I'm sure it's time, but I'm trying to figure out what direction I should go from here to start chasing this problem down now. I have read the random posts and watched the random videos about this code and what it potentially could be, and if like to try this the best way I can and not just jump in and start taking it apart and not have a direction to go with it. Any help with what the best route to take on diagnosing this problem will be GREATLY appreciated.

Gumby22

If you’re still needing an answer….

Remove the fuel rail, clean it, and be prepared to replace the #7 injector.

The fuel rail sits at a slight angle with the lower end at the rear of the engine. Over time, debris and/or water from bad fuel accumulates in the end of the rail until it eventually reaches the #7 injector, causing misfires.

At best, you’ll just have to clean the rail and injectors. At worst, you’ll have to replace the #7 injector. Make sure to replace the o-rings and clean the ports in the intake manifold also. Grease or Vaseline will make reassembly easy.

There are no inline fuel filters on these trucks (at least not from the factory), so I’d recommend directing the fuel line into a bucket and running the pump for a few seconds to flush the line between the tank and rail.

oilcanhenry

Gumby22: although I tend to agree with you, this man might have an injector that's partially plugged. A good injector cleaner might help out if he's been using cheap fuel. Chevron Techron or Lucas fuel injector cleaner would be best. I am not a fan of Seafoam as it doesn't seem to work near as well. As to Vaseline or chassis grease, I'd never use either one on an engine. Dialectical grease would work, but I would not use it on an intake manifold gasket. Those are my opinions only, so please take no offense, as I have seen you give out great advice to many people posting here.

Gumby22

I hope your opinion was worth it, for now you have incited my wrath….

No offense taken at all - the whole point of forums like this is to provide community input. I just do the best I can to provide factual information and guidance when I can because one of the reasons I got into this field is to help people that need it; plus, it helps me learn and improve my skill set and knowledge base.

The other side of the coin is that I don’t always have time to get as detailed as I’d like to, as my free time lately seems to only be available in 5-10 minute increments.

The reason I suggested rail removal instead of just a cleaner is because a cleaner might be enough to restore injector operation temporarily, but it wouldn’t be a permanent fix because it wouldn’t clean everything out of the end of the rail and the misfire would likely return in a short time. Removing and cleaning the rail is a solution that would ensure the contamination is removed.

As for brands or types of cleaners, they all have advantages and disadvantages. Any of them work well for preventative maintenance. I’ve tried several off-the-shelf fuel system products and I’ve learned that the ones that seem to work best are the ones you can smell when the engine is running, meaning there’s a noticeable odor after it’s been added that only lasts as long as the concentration is strong enough to produce it.

I’ve never experienced negative effects from different lubricants for FI o-ring installation. I use whatever is available when I need it, but I’ll try to pay attention in the future and see if issues start happening.

cshadows74

Ok, here's the update. Replaced all injectors, plugs, plug wires, and coil packs. Ran normal for a couple minutes then started missing. Got 2 of the off brand plug in afm deleters. Yes, I know these are hit and miss if they even work, but I got these for free and thought it was worth a shot. First one made no difference. Plugged in the second one and it ran normal for a couple minutes and then started miss fire in 7 again. Compression test on 7 was 145 psi on the third stroke it hit, and went to 150 on the next time it turned over. We removed both valve covers and everything is moving like they are supposed to. I'm running out of options to check here. Injector 7 was horrible with build up and that plug was covered in build up. All other old injectors and plugs looked normal. It seems like the misfire gets worse as it warms up. Scared to let it run for too long though cause Idk what else could get damaged. Has a little smoke coming out the exhaust that I didn't have before, and it doesn't have a specific smell, just like exhaust. Really don't want to have to take this somewhere to find the issue, cause I know they'll go straight after the afm, but I'm still not convinced that's it because it never goes in limp mode, but I'm running out of ideas.

davidjohn

Most engines have a 4, 6, or 8-cylinder engine, where more cylinders typically mean more power. Power is generated by pistons that move up and down while fuel is ignited at very specific times. A misfire typically occurs when the timing of this ignition is off. P0307 indicates that cylinder #7 is experiencing misfires

Gumby22

Since replacing the injectors and plugs, have you gotten any codes except for P0307?

Did you check compression on any other cylinders? 150 isn’t necessarily bad, but if other cylinders are pushing 165 or more, then compression on #7 is low relative to the other cylinders and a mechanical problem should be pursued. You should at least check 5, 6, and 8 as a reference. Check #7 again at the same time - compression testing needs to be done when all the cylinders are at the same temp.

Are you certain the rocker arms are moving through a complete stroke? The cam lobe(s) can be partially rounded off and still be opening and closing the valves, but not enough to provide adequate air flow for proper combustion. Use a dial indicator to verify the #7 rockers move as far as another cylinder that isn’t misfiring.

Nobody is questioning that this is a misfire - we’re trying to help the OP narrow down the cause.

There are multiple causes of misfires ranging from electronic to mechanical - ignition timing can be dead on but if there’s a reason the cylinder can’t seal properly, or if a fuel injector is stuck open, a misfire is still going to occur.

zigblazer

Did you ever find the cause? I'm having the same problem with p0307 and a consistent misfire. Replaced injectors, swapped most other parts, checked rocker movement while running. No problem found.

cshadows74

Yes. It was one of the push rods on a lifter over 7.it moved until it got warm. That is why I didn't see it to begin with, I only turned it over to make sure everything moved. I didn't start it. Will, long story short after we found that, the way it was in there, it messed up something on the cam and here I sit now with a new Jaspers without the AFM. It's been a big cost, but the rest of the truck is in great condition and I have no reason now to want to look for anything newer for awhile.

Steve s

I had random and cylinder 7 misfire codes due to the Vapor Canister Purge Valve Solenoid stuck open.
Take a look.