Anyone ever resolve this issue, Im having the same issue. New coils, new mag wires, new champion plugs, new block, new 02 sensors and still Im getting P0306, P0300, P0301, P0306, P1300. Im about fed up at this point.

 

You've contributed on my threads lately so you know I've had issues with a stuck injector and a bent valve. The latter caused by me.

I'd check the compression on that cylinder and a known good one. If it is low, then it has to be the valve or the Rings. If not, then smell the oil. If the oil smells like gas, I'd consider a new or remanufactured injector.

Doesn't sound like a head gasket but you know that's right next to the water passage.

 

Today I did a little more work on it, pulled the spark plugs at number 8, it's reading rich based on the plug color. The question is whether it is the chicken or the egg, is it rich causing the misfire or is it because of the misfire. I tend to believe the former.

I swapped the plug wires on the coil from cylinder 5 to cylinder 8 and confirmed that it is definitely a cylinder 8 issue only. Also put yet another plug wire on cylinder 8 to make sure it is not a wire issue.

Next up is a compression check on that cylinder, however I don't believe that would result in it running rich at idle, the only thing I can think of that would do that would be some sort of misfire in the injector pulse coming from the ECU. Will probably swap ECM with my other 03 tomorrow.

Observing that it is rich I believe rules out a vacuum leak only on that particular cylinder. I suppose my reading of a Dark Spark Plug could be a mistake and be oil fouled instead but I don't believe so. It is still not drinking any coolant so I am mostly ruling out a leak to the adjacent coolant Passage.

 

That is very strange. In my little decision tree the only things that unify all evidence is that the plenum gasket isn't sealed as to that cylinder only, and that's basically impossible, or a valve/ring/compression issue, which you can start to confirm or deny with a compression test. I'm sure your spark plug is gapped correctly.

Or you have a bolt in your cylinder. Haha that's a joke.

 

I did some thinking about this during my miserable day swapping heads.
If your compression on 8 is good and in light of all you have done and your observations stated in this thread, it has to be a problem with the 8 injector, either not spraying gas because it is partially clogged or the o ring(s) have disintegrated. Does the top of the engine smell like gas at all? If so, probably an o ring. If not, probably an injector that doesn't spray good.

I'd check the compression. If it is good, then pull the upper intake and fuel rail then swap injectors or put a new one on number 8. But you'd need a full set of o rings if the o rings are any concern because removing the fuel rail will disturb all of them and move your woe to another cylinder. I've re used plenum gaskets with copper coat on them, but I'd also want to have a new plenum gasket in hand.

 

Well, found the problem. Low compression on #8. 130 dry, 150 wet - 170-180 on the others. I find it unusual that only one cylinder would have a piston ring wear problem, but maybe someone drove it with a badly blown head gasket too long and wore the rings out? Truck drives ok on the highway, not really any worse than my other two.

Oh well, I am out of time fooling with this truck - accepted a job in Lynchburg VA and won't have time to fool with this during the relocation - look for the truck sale post in the classifieds section.

 

I'm sorry to hear that.

It could be the valves or the rings. Such easy parts to replace off the truck and so difficult on the truck.

Sad news.

Just throwing a little pitch... You can get those heads off on a Saturday and have all new rings on a Sunday. If the heads hold water they'll probably hold compression...

 

Probably rings, compression does not usually improve wet (oil squirted in the cylinder) if the problem is a valve issue.

I definitely think it is probably worth fixing, and you are right it really isn't that big a job in the truck. I can have heads and pan off in 4 hours, about the same going back. Rings relatively easily replaced in the truck also. One of the things I like about these trucks is they are relatively simple and easy to work on, but I am just out of time on this one so in will have to be on someone else's to do list.

The rest of the truck is really in condition that begs for a full 4.6 rebuild, as you just don't seem many that look and drive this good inside and out.

I may yet wind up rebuilding/replacing the engine, but first I will see if someone else would prefer to have it