I'd suggest trying some standard copper NGK plugs to see if your issue goes away completely.

 

There are two coil packs, with 5 separate coils. Each coil will fire two cylinders, one on the power stroke, the other on exhaust. Electricity follows the path of least resistance, thus the plugs what have the easiest ground path, will get the lions share of the energy. That WILL cause problems..... Either change the rest of the plugs, or put 'em all back to copper. having a mixture is going to make troubleshooting even MORE complicated.

 

I would put the old plugs back in just to verify it is a plug or related issue. They were known for breaking rocker bolts and it does make a decent amount of noise and runs rough, not pleasant when you are an hour from home.

 

One of the original plugs broke when being removed so I can't go completely back. I bought some OEM style copper plugs and returned the NGK's. Gap set to .045 and still too much predet. gapped to .060 like the originals and still have a little predet but only under high throttle for about 500 rpm at around 2500rpm. I read the 5 coil/2 per plug thing above and am thinking I will get the gap all the same and see how it goes. I haven't pulled my travel trailer in the last 12 months and am a little worried since I was going to pull it next month so I need to sort this out. Also wondering if my cats are a little plugged up, just doesn't feel like enough power. It's got 70k miles so it sits a lot. Anyway just keeping the journey I'm on documented in case I learn something (like the coil thing, didn't know that).

 

Changed all the plugs and wires, all gapped to .060, runs almost with no pre-detonation. Measuring the Motorola all copper plugs resistance versus the champions I took out they are about 2k ohms difference so another fun fact, use the same plugs throughout. I'm going to check fuel pressure but am sure that's not an issue. The cats or a cat used to make a rattle sound occasionally and I'm thinking those are gone. Watched the O2 sensors on my reader today during a short drive (they were replaced about 10k miles ago or less) and readings look ok along with %. Since the cats are more or less welded in and I'm in Cali, I'm going to replace those next and update this forum after that. A neighbor chatted me up about a cat cleaning liquid he runs in his SUV periodically that is supposed to clean out the cats. Anyone used such a thing. Like Cataclean or Liquid Moly brand? I'm guessing mine are to late and may be the result of leaking injectors etc.

 

I would do a backpressure test before just replacing the cats out of hand.

 

Also, before replacing the cats, I would be tempted to run some Seafoam or water through the throttle body to help de-carbonize the engine, since carbon deposits from lots of short trips can cause pre-ignition. Listed below is one example and there are several other videos out there discussing the process..

 

I am going to get the back pressure checked to see if the cats are plugged. I have done everything else including checking fuel pressure etc. Tried running all the random chemicals through it everyone reco's but nothing helped. After running it for 30 minutes or longer the exhaust starts cracking (sounds) and the engine runs worse and worse. The cats or the pipe leading to the cats at least on the passenger sid make a ton of nose. I'm thinking I may cut out the exhaust after the cat and prove the issue.

 

Have you tried running it with the front 02's out?

 

Final update on this, I'm in California, the worst state to have this issue but I found a muffler shop that would listen to me and dropped it off. They checked the O2's and other things and called me. When I dropped it off I told them, no fuel pump issues, new plugs and wires, O2's changed 2 years ago, blah blah I want you to check the cats or back pressure, they checked O2's etc. (I already checked both the voltage and the OBD1 from the O2's) and told them nothing wrong with the O2's, so I drove over and met with the guy running the show, he said we checked it and couldn't find anything wrong, I said cut off the cats and check them out, it's OK with me. He calls after the new year and says they are blocked and that was the problem. He sticks in a straight pipe for both cats and yeah it runs perfect now. I am now calling the Ref's in Cali to get their reco on a "approved replacement". He couldn't ID a Cali approved replacement. Reminder I have a 2001 2500 4x4 EPA V-10 heavy duty, not the Cal version. I'm hoping when I call the Ref's they will say, oh yeah buy these cats, if not I have to reinstall these useless cats (which the muffler shop will gladly do for 350) and go get it tested every two years and then have them removed until the next test so I can drive the truck. California is in fact the worst place to try and keep a truck on the road. I'd happily install any cat (there are 2) to remove emissions and keep the earth going but no, they want to approve the cat first if that's even possible. So FYI, I have cats that will pass emissions, I'll get them added back for 2 days every 2 years so I can tow my trailer in California,,,,, unless the ref says, no worries, buy this,, and you'll be OK....... This truck has 70k on it, it's a 2001, I use it to tow a tow hauler every 2-3 months. C'mon man....