Pull the injector wires off one at a time while the truck is running. The noise should lessen when you hit the cyl that is generating the noise. If it does it more than likely is a rod bearing. A rod bearing on this engine is not a real heavy knock as you might think unless severely damaged. I doubt it is piston slap as it should go away as others mentioned when warm. Take a piece of hose or a stethescope and move around the engine and get an accurate idea where the noise is coming from. Listen around the oil pan also. If it is a rattling noise, like a marble rattling a round under the cam cover it could be collapsed lash adjuster. Which could cause driveability issues. Behind the front cover could be a chain tensioner collapsed. Not likely a chain guide though as they tend to wear very little and not much noise would be generated from it. I have heard some guys on this site change the PCV valve for knock concerns and solve the problem. I usually don't have luck like that myself though. Good luck.

 

Faster150, you said could be fuel timing. Are you talking about injector pulse signal from the PCM? Is there a reflash for this problem? For the record, I always run midgrade gas, cleaned the EGR tubes, cleaned the EGR, changed fuel filter; no difference.

 

My 98 4.6 did the same thing. I just put in it what I always put in my deisel, lucas oil treatment. It looks like a bottle of gear lube. I recommend getting it a little warm before putting it in the truck, it is very thick. 50k miles and have not done it since and no noise. I use a heavy oil though. I am a castrol fan. 180k miles on it now.

 

Did that take care of the blue smoke at start up too?

 

Would like to know this as well. Thanks.

 

Well I filled the tank with 92 octane premium and added 12 oz. of marvels mistery oil to the gas. I also added one bottle of stp oil treatment to the valvoline 10-30. After driving about 100 miles the noise is almost gone. I have to put my ear in the wheel well to hear it. I would say it was a 80% reduction in the noise. The only problem is I don't know which thing made the improvement. I think it was the stp. Hopefully it will go away completely.

Budman

 

I hope for your sake it gets better. I will be surprised if it does though. I suspect the heavy STP is just keeping a rod bearing from hammering as much. I could be wrong and hope I am but I believe the noise will just get worse again. If so don't risk throwing a rod through your block. Drop the pan and check the rod bearings. Use some of the ideas I mentioned above for trying to locate the exact cyl/rod that is generating the noise. Good luck.