2000 5.4 with 165,000 miles.
Fairly new COP's.

Started to run rough so I punched it for a while.

Pulled over and it smelled like sulfur.
No codes so I thought it might be the cats. ran it a number of times in the barn and it acted like the cops were wet, although there was no sign of water on the engine or under the hood when the issue first started.

Finally got the SES light to come on and it showed three codes = P0303, p0305 and p0306 which were mis fires for the 3,5,and 6 cylinder. Cleared the codes and drove a bit aggressive down the dirt roads to pull some more codes. SES light again flashed and codes p0300 and P0306 came up. The 300 code is multiple mis fires.
I then jumped out and slid under the truck, i could feel the heat from the cats thinking it was excessive. Then I could hear them cracking like crazy.

Finally my question: Could it be the cats or could the smell come from misfires???
Any help would be greatly appreciated. i am thinking of cutting all the cats off. I was going to pull the pipes off but the bolts look like they have grown a lot of fur over the years.

I am not sure if the cats are clogged up that it would cause mis fire codes either.

 

Cats are burning up because your soaking them with raw fuel. Truck may be Limp mode. - Hard to say. Not enough info. To many variables.

Start with the new fuel filter and run fuel system diagnostics.

 

Thanks jbrew. Anything I need to know about the fuel filter replacement or is it as simple as a couple of wrenches?

 

check the coils for bad con. or check the plug boots sometimes those things hold moisture like crazy! if that dont help it very well could be bad cats there is a way to test with a pyrometer. i would check the coils with a oym meter first though.

 

I thought it would be a good idea to powerwash the engine last year and had a major misfire issue so I replaced all the COP's and have had no issues regardless of weather. Chances are the coils and boots would be good but I guess I could pull them off just to make sure. Thanks for the tip.

 

He has newer coils and a MULTI METER tests resistance ONLY. That won't reveal a bad coil in most cases, you would have to have Primary failure and that hardly ever happens. Coils are tested by monitoring cylinder history and/or bench tested w/the Rotunda kit (1-800-rotunda).
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z67 - always rule out fuel issues first. It easy, not expensive and you don't have to rip the top of your motor off to do it.

BTW - You need to get a Haynes or Chiltons Manual for that model - it's a must.

 

I have to trust you jbrew. You have been correct every time I have posted an issue. My major problem is getting my son to the motocross track race this sunday and I am running out of time. This is the only way I can get him and the bike there unless a have a friend drive us out there. I will try the filter tomorrow and see what happens. If not I might try to cut in front of the cats on both sides and see if it runs better. If not I can have them welded back on but I am in a hurry to get this thing on the road. The race this weekend is about 50 miles each way so I want to make sure it will make it.

 

Mann, Idunno lol. Try the fuel filter. I don't have to much faith that is the problem, it could be. I think there's more going on here. Your NOT missing @ #1 cylinder. A bad filter usually pics on #1 first , being the furthest away from the pump.

Personally I wouldn't drive, start or attempt anything with the engines current condition. You could very well cause more damage doing so and it may even leave you stranded in the process. I would have to go thru it with those problems. Something unordinary is going on given the DTC's posted.

Yea, it could be the coils or maybe the wrong the plugs ? Not sure, I didn't install and I don't know what lead up to these problems. - (Sounds like someone washed the motor?) (But I'm sure you would have mentioned it IF.)

Having three misfiring bad enough for the PCM to catch is a pretty serious problem. You could be Limp Mode -But why? Was she getting hot? Any other DTC's recorded in the past? Well,- Limp mode shuts down injectors and/or limits fuel delivery. Your DTC's coincide with this.

It could be the Fuel Pump as well. You need to definitely rule out the fuel supply and regulation first.

I would explore other options for the race this weekend - The trucks sick right now, might take some time/work/and cash to heal.

Good Luck

BTW- No need to drill those cats IMO. If by chance you are with out a doubt , positive they are sealed - Remove and replace or just install a piece of pipe in their place. - For now anyway, then take care of correctly at a more convenient time.

Cats seal when they heat up. Raw fuel soaks them/ they ignite and melt the brick thru-ways/cones together.

 

They might be clogged but only because you truck runs like crap. Clogged cats are a big symtom of other issues they arent causing the missfires and all. Cats last along time on well maintained engines..

 

Well this time I can say I did not wash the engine. I did learn not to do that after the last time. I replaced the plugs with OEM but purchased the cops through ebay, it was suggested on this site to order them that way and I did not have any issues until now. It was running fine on my way over to a friends, about 8 miles away, then when I left his place it started to run rough. I did not use the dielectric grease and maybe that could be part of the issue????? I saved the original cops so I could exchange if there were any issues but with the codes I got on three I am thinking it is something else.

 

So you never had any over heating going on? WTF, this is a strange one lol.

Well, take a a look at your DPFE lines, look for burn thru or heat deformities.

Plugged cats will heat the hell out of the EGR pipe. In-turn - melts anything other than metal that may be around it.. If your cats are truly in that bad of shape, you may have melted or damaged a section if wire harness.

I've seen that happen before, but it was an explorer - 4.0 I think.
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Maybe the EGR valve is stuck open..? You should have poppet valve failure DTC's tho, otherwise I would have mention that before. Yea, - you can suck test that to verify that it's operational.

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It's running rough @ idle right? - While she's running rough, grab the harness over by the AC accumulator. Move the harness further away and listen for any defection in idle - Does idle smooth out some?

The Magnetic field can create havoc on the ignition system. Especially if the harness has dropped/sagged a little more for some reason.

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That's about all I can think of that might cause 3 cylinders to go buggy at the same time.

I hope someone didn't thro some goodies in the tank while you weren't around lol - Make sure there isn't a Potato shoved up your tail pipe. I know, that's a stretch, but you never know lol.

Don't forget about the fuel system check as well.

 

Cutting your CAT's off is not going to solve your misfire problem. It just leaves the door open for you to keep dumping excessive fuel into the engine.
Jumping on the pedal like you did only made the situation worse by dumping the extra fuel into the system and the end result is burning up the CAT's (possibly !!).
The #3 cylinder misfire can be caused by various problems. Excessive oil dripping down in the chamber from adding oil and a little spillage when filling.
I just went through a problem with a heater hose leak but that effected my #4 cylinder but I could see it causing a problem on #3 depending where the leak is in the hose. (just something to check for)
The baffling part about this is you have misfires on #5 & #6.
Your heading in the right direction by pulling the the effected COP's and placing the old ones in place just to make sure. I had to do that on my #3 cylinder once, but for different reasons. I think that after going through the hassle of pulling the COP's, while your in there, pull the plugs and take a look at them.
I just went through this same situation on my Mom's Jeep Cherokee 2 months ago.
Check the primary resistance on the 3 injector's that are having a misfire problem. You should get between 13.5 - 19 ohms (per my haynes manual)
(She was getting a much different reading than the other 5 cylinders. I changed out the #1 injector on the Jeep and it has been running perfect ever since.)
Fuel filter should be changed as normal maitenance anyways but I don't think that is your problem.
I am leaning towards you possibly having some moisture down in the chambers. Just a little bit will sit down there and cause the Spring Connector inside the Coil boot to cause massive misfire problems. I am going on experience here with the little bit of coolant that was dripping in my #4 cylinder.
Lastly, if you can get a friend to take you and your son to the race track, I would opt for that. If you don't clear this issue up you may not have a truck to take him racing this season. That is, if you insist on driving it by just removing the CAT's.

Good Luck with the repair & good luck to your son at the race.

 

Thanks man. I just don't understand why this started to happen all at once. Last time my engine ran rough was because of my own doing but this time it was like someone clicked a switch. One thing I may not have brought up is when I first walk in the barn and fire it up it runs nice and smooth. Once the idle comes down a bit, it will run smooth at about 6000 rpm no problem. As soon as it starts to warm up, 5 minutes or so, then it will start to miss. I thought that may be another indication that the cats were plugged but I am lost. Regardless, I will not drive it until this is figured out.

 

I have opened cats removed the core and welded it back together during diagnostic process, I don't recommened driving it that way though, for one, the o2 sensor behind the cat will send the engine signals to lean out mixture which can lead to even more damage

 

Excellent point !!!!