In between rain showers I put my OBD II reader on and found no codes and no pending, this after we had run the van for approximately 1/2 hour. Then pulled the individual spark plug wires from the coil packs one at a time and started the engine for each. There was no change in the knock so I'm pretty sure between that and the Lucas motor honey not making a difference that it rules out a rod bearing. The oil pressure gauge remains about 1/2 way up the gauge after the engine is warm so I believe that rules out a main bearing too. Next we are going to try and locate the VCT solenoids so we can disconnect them to see if the VCT has any impact on the noise. They aren't as readily visible as what I find on the internet for cars and trucks, I'm thinking they may be hidden behind the coil pack mounts on this van. Still need to check the crankshaft thrust tolerance and the harmonic balancer but will wait until the driveway is dry.

 

I believe you don't have any VVT system on your year vehicle..
If it is a rod bearing ,they don't give any codes for that although the knock sensor could retard timing and produce a low power complaint.
The best way to verify a rod bearing is to take the load off it by grounding the spark to the cyl in question..
A maim bearing produces produces a heavy rumble nothing like a rod knock.
Sometimes a piston slap can produce a noise that some confuse with a rod knock. You can diminish a rod knock , but not a piston slap.

 

Hanky, I can't say for sure that it has VVT/VCT but according to the VIN it's a 4.6l made in Romeo, Michigan, and what I find on the internet is they were used in Ford vans from 1997 -2003. I'm not a Ford guy so I'm feeling my way along as we go. I'll know more once it stops raining and we can get back to work on it. We are going to have to pull the coil pack mounts off to see the front of the valve covers where the solenoids are located.
Wouldn't what I did by disconnecting the spark plug wire from the coil accomplish the same thing as grounding the spark to the head? No spark to the cylinder so no combustion.
I never considered a bad knock sensor but will add it to the list to check. I'm perplexed as to why it was parked in the driveway running fine one night, and the next morning the knock starts immediately upon start up. Thanks

 

You brought up a good question and I hope this answer will help you.
The reason we don't just pull off a plug wire to isolate a cylinder is ,when you remove a path for the current to get to ground it will find another way and in the process it will destroy the ignition module.
Hope this will help prevent additional problems for you.


One thing that might cause a knock on start up is if the oil pressure regulating valve becomes stuck momentarily , it can cause an oil starvation condition that would not immediately be shown by the oil pressure light.

 

Thank you for the explanation and I understand the ramifications of doing it the way I did, however for the purpose of "deadening" each cylinder for a mere few seconds to see if the knock went away, knowing that I could damage the coil pack was worth the risk. Some of the plug wires are a bear to get to, and off and on, even though we have put dielectric grease inside the boots. In hindsight I should've taken an old plug wire and used it to ground each terminal individually as I tested each cylinder.
The prediction is for the rain to stop tomorrow morning so we can get back to troubleshooting by the afternoon. Fortunately both the van owner and I are retired so there isn't a time crunch.

 

Just a reminder, a few seconds to electronic parts (IGNITION MODULE) can be a lifetime, never worth the risk , no shortcuts !!!

 

Hanky you were correct, this 4.6l doesn't have VCT even though I found several sites on the interweb that said it did. I also made a jumper wire so I could individually ground plug wires but still didn't quiet or change the loudness of the knock after doing all 8 cylinders individually. I inspected the crankshaft harmonic balancer and the rubber looked intact, and observed it while the engine was running and there wasn't any wobble. Forgot to check the thrust clearance on the crank so will have to do that.
Pondering the possibility of piston slap; shouldn't the knock noise decrease when I removed the spark since there isn't any combustion going on? Again, this knock started immediately upon start up, not like it started as a tick and got louder. Any thought on how to determine if it is piston slap? I had a Ford mechanic tell me to spray oil down the throttle body, just not sure how to do that unless I use something like WD-40.
I've thought about the old trick of draining out a couple of quarts of oil and replacing it with transmission fluid to see if we might clean out something that has gotten plugged. At this point I'm grasping at straws and resolving ourselves to looking for another truck. Thanks

 

I have more than once added some ATF to the engine oil to get rid of a stuck lifter and it worked.
I don't know of any special test other than sound for a piston slap.
No disabling spark to a cyl will affect a stuck rapping lifter. The knock is just double the frequency of cyl firing.

 

Hanky, saw online where a loose spark plug could cause a piston slap knock so today we went back and torqued all 8 plugs to 20ft/lbs. None of the plugs seemed loose and it didn't solve the unknown knock issue. Surprisingly the spark plug boot on #8 was damp with water residue on it. No idea where the moisture came from. We haven't experienced water loss that we can detect, We haven't had rain for 3 days nor has the van been driven. For water to get down into spark plug well is worrisome. Any idea where it might be coming from? Not sure how the water routes through the engine.
Going to try the automatic transmission trick tomorrow and drive it locally to see if it helps. Thanks