Last camping trip of the season for us this weekend, Knobels Grove for halloween. 09 Chevy Suburban with 5.3l. Pulled a hard 3 mile long hill it works the truck good but doesn't usually have a problem . I melted the spark plug on cylinder 4 tonight. P300 and 304 codes. Replaced plug, cleared the codes, left the trailer and returned home. 304 is an injector issue code. If the injector quit would the plug end up like this? Or if the injector was feeding half the fuel? I filled up with e85 tonight, I wonder if that caused this.

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Was this #4 plug threaded in tight when you went to unscrew it?

 

Yes, the plug was tight

 

Here are a few thoughts I have come up with on this. If they don't make sense, maybe they'll at least provide a thought process to the actual solution.

* The #4 injector may not be atomizing like it should, providing reduced fuel delivery (like you stated) -- certainly reduced efficiency, if this is the case.

* The #4 hole is a deactivation cylinder. Perhaps the injector is caked up with something, unable to close all the way. When the cylinder goes into deactivation, the dribbling fuel accumulates, then when #4 is turned on, the combustion is not taking place due to flooding or if it is taking place, it's not at all efficient. However, you stated you were giving it a good work out, and that means that deactivation wouldn't have taken place at all.

* Check compression of #4 hole. At idle, anything under 90 psi is inefficient. In fact, at idle, with less than 90 psi, you'll probably notice a miss with engine bounce. Either of the lifters may intermittently not be allowing a valve to close or open all the way, providing poor combustion.

* The #4 spark plug may have been defective, which can certainly happen on rare occasions.

* Something entered into #4 cylinder and has attached itself to the combustion chamber, a valve, or the top of the piston, providing a hot spot and causing detonation.

* Pour quality spark delivered from coil, due to a weak coil or a failing plug wire.

* The #4 plug was loose in the head (but you said it was tight).

Maybe this will help some.

Kevin

 

If the plug was loose does that not allow the plug to transmit heat to the head properly, like a valve stuck open?
I did a compression test and warm it made about 30psi. Could the afm not allow the valves to close all the way? A friend ran some plugs out to me and I replaced the bad one, cleared the codes and I turned around and pulled the camper about 7 miles to his house. The truck ran smoothly and did not throw a code until I was at his driveway. I dropped the trailer and drove 45 min home, with a miss.

 

In the past I did have issues with the plugs coming loose, I check them periodically because of this. I guess the best way to see whats up is to pull the head.

 

Coincidently, may have two issues going on here: a loose plug and low oil pressure.

The 30 psi may have more to do with the intake valve not opening far enough during the intake stroke rather than a valve stuck open during the compression stroke. Here's what can happen.

The o-ring on the pick up tube going into the oil pump splits or breaks. This causes low oil pressure to the entire system -- to all lifters, including the AFM lifters. Even though all 8 AFM lifters are the same, one of them can act up first before the others due to variances during manufacturing. It seems that an AFM lifter exposed to low oil pressure can actually become shorter than a lifter operating at normal height -- most likely due to galling. The lifter, now collapsed, cannot open the intake valve all the way to provide the adequate volume of air needed for proper combustion.

As you mentioned, a loose spark plug cannot transfer heat sufficiently to the head and can then become overheated.

If what I have described has happened to your engine, I would replace just the one bad AFM lifter and the o-ring on the pick up tube.

Chances are your cam lobe is okay, but having a lifter roller bounce up and down on it will eventually gall it. This could have easily happened to any of the AFM cylinders: 1,7, 4, or 6. It just so happened to fall upon #4.

I hope this helps. I've been through this.

Kevin

 

. . . an additional thought.

Pull the passenger side valve cover. If you have a loose rocker arm on #4, you have a collapsed lifter.

Kevin

 

Wouldn't it be a good idea to eliminate the afm completely if I have to open it up?

 

You could eliminate the AFM system, that's up to you. If you're going to keep it long term, then spending the extra on the delete kit might be your way to go. If you plan on sending it down the road in the next year or two, maybe spend the $600 or so and fix it with the AFM in place.

If you do eliminate the AFM and diving that deep into it, I wouldn't hesitate to put in new pistons as well. The reason I say this, these engines are known for developing piston slap. GM has bulletins on the matter saying that it's nothing to worry about. They're right, but it doesn't change the fact that when your engine develops the sound, it sucks. The reason these engines often do end up with piston slap is because when GM made the pistons shorter in height, to reduce weight, they needed to move the connecting rod wrist pin closer to the center of the piston. The slightest amount of wear from the skirts brings the noise. Years ago a greater offset provided better control of the piston during its vertical movement.

If you fix it with the AFM in place, you could start at 8:00 a.m. and have it done by 3:00 p.m. with the engine staying in place. If you go deep, you'll be looking at many more hours and a couple of thousand dollars with a bit of custom tuning.

Kevin

 

Thanks for the advice Kevin. I pulled the valve cover tonight and didn't see anything unusual. Pulled the intake as well and hopefully tomorrow Ill get the head off.

 

Pulled the head. Didn't find anything unusual. Unless the exhaust valve is not sealing properly i don't know why the compression was low. If the lifters were not providing full lift is there a way to tell if they are bad?

 

The valley cover bolts were loose, most of them not even finger tight. Would that allow oil pressure to bleed past the gasket and cause the lifters to not work properly?

 

I'm not being a wise guy, but I have to ask. Are you looking at the right hole? The driver's side, starting at the front of the vehicle, is 1, 3, 5, and 7. The passenger side, from the front, is 2, 4, 6, and 8.

Typically, when a lifter collapses, you end up with a loose rocker arm. You mentioned that this was good. You can pull the two lifters from the #6 hole and compare them in length.

The bolts being loose on the valve lifter oil manifold (VLOM) could cause low oil pressure so that the deactivation of the cylinders won't take place properly. Although, without oil pressure to the lifters, the engine stays in V8 mode. With any significant loss of oil pressure you would notice it on the gauge and the message center will display a message stating so, telling you to shut off the engine. Do you recall what your oil pressure gauge read? If the gauge didn't register anything, the o-ring may have split at the pump and needs to be replaced.

With the head lying on your bench, face the valve buttoms toward you. One at a time, shine a pen light from the back side into the intake and exhaust port runners. Insert the light as far as you can go. Look for a sliver of light around the valve seats. A sliver of light can explain a loss of a good 50 psi.

Also, examine your valve springs. A broken spring can keep a valve from closing tightly, allowing a significant drop in compression.

As long as you have the VLOM off, replace the small cylindrical oil filter in the port below the oil pressure sending unit. A 5/16" x 3" bolt inserted carefully into the hole can be used to retrieve the old filter. You can buy a new one at a dealer or a parts store.

Inspect the piston top for a hole, crack, or other damage toward its edge. This will reduce compression as well.

With #4 lifters removed from the engine, inspect their rollers for damage. Also, inspect the corresponding cam lobes, mainly to see it they're still intact and don't appear galled.

Note: You'll need new head bolts when the time comes to reassemble. They can only be used once.

If nothing jumps out at you as to what is going on, maybe check two more things for sure. Try your compression gauge on another cylinder to make sure it's working properly. Also have the head checked out at a machine shop.

How did the head gasket look? They usually don't go bad on these engines. It's actually quite rare if they do.

Kevin

 

Lol, no offense taken. This is the first ls engine I have been into and I confirmed the cylinder orientation before I replaced the injector. The top of piston looks good, I see no holes or cracks. Could the rings be broken? There was a small glob of something glued to the piston top, may have been the ceramic insulator from the plug. There is a fine scratch on the cylinder wall but I don't think it is significantly affecting compression. I replaced the oil pressure sender and filter less than a year ago and it is still clean. This morning I put the head in my work truck in hopes of having someone look at it today. Looking across the tops of the valve springs the #4 intake is sitting higher than the rest. And when I compress the spring by hand(as much as I can) it feels crunchy. Maybe the valve seat is bad.

 

I did look at the cam as best I could. I looks more worn than I thought it would for a roller. It does have 130k on it but its not galled or pitted