Leaning this direction. Have to go pick up the yappers from tennis camp tomorrow, then Saturday drop in the O2 sensors and ground check. And deliver a 12-pack

 

Sounds a lot like the symptoms my former F150 had after the CAT hit something off-roading. A piece of the honeycombs broke off and would randomly turn/move in the in the outlet of the CAT so it was restricting exhaust flow, otherwise it ran perfectly.

If that isn't the problem I agree with everything suggested above, good advice.

 

I'm leaning towards catalytic converter(s).
I had a similar story, albeit without the intermittent aspect.

I am the 2nd/3rd person to suggest this to you. Have you checked them? On my van I was able to get a very decent visual down into the pipes.

If you hit the(cold) cats with your hand, can you hear any rattling?

Chasing grounds and O2 sensors and data logging strikes me as far less likely than bad cats.

 

Not able to do anything with it this W/E, a failed hot water heater derailed my plans.

I'll check the cat this evening. I too have suspicions it may be the cause.

 

zapola6, twigsv10, and im50fast (btw I'm 50 fast too). You guys win!
Took it to the muffler shop to do a flow test....plugged cat. WOOT! That's the good news, besides a $550 replacement cat. The bad? news is he said there was a real strong raw fuel odor in the exhaust and that I should get that fixed or we'll be replacing it again. That's news to me because MPG's have not changed, other than towing, and you cannot smell it out the pipe.
I have a friend with a wide band o2 sensor that I an thinking about installing to verify.
Anyone have thoughts about this new revelation?

If I get past this and this thing wakes up, I'm going to wear my credit card and the UPS guy out on upgrades.

 

You can have an idle misfire and not notice it much, and while running off-idle, it's not even there so MPG doesn't suffer.

When was the last time you checked the plugs?

 

Man, I REALLY hope this turns out to be your problem and the fuel thing is just a fluke!
Looking forward to hearing some reports after a few miles.

 

Trust me brother, I hope this is it!
Plugs replaced about 3 years ago, but not many miles ago, on the long side maybe 50K. And the scanner does not pick up any misfires. BUT, if this is fixed, the TLC we're going to dole out will be amazing.

Just got off the phone with my mechanic and he was not surprised with the raw fuel smell.

Cat is ordered, will be here Tuesday. Thinking I will will put Motorcraft O2 sensors in at the same time and reset the 'puter to let them learn to love each other.

Then...oh boy, then...

 

You found that fast! Hope it treats you well after it's fixed.

The 2V V10 in my experience without the CAT has a fuel rich smell but worth checking out to avoid further expenses. Fuel pressure regulator, MAF sensor, O2 Sensors and misfires (The computer won't necessarily see them) are all things I would check.

Then again like I said before it could have just broken a chunk of the honeycombs, you won't know that until it's removed.

 

Good news PROSTOCK.
Get pics.

Also I did cat-delete and don't regret it, except for the foul-smelling tailpipe and slightly increased cabin noise.

 

How do you get around the CEL without a cat? Or do you?

BTW, I'm not claiming any victory yet, but I did finally find something wrong.

 

If it's been 50k you might consider changing them or at least checking the torque.

There is an exhaust back pressure tester available on ebay for $24 that looks interesting.
It plugs into an O2 port and measures the exhaust pressure.

If you're feeling an occasional misfire at idle the computer will not set a code until it detects many misfires.

 

Sweet.... Found the big issue.... Fuel problem may even clear up now that the V10 can breath... Or the fuel problem caused this problem.... Now I'm just making it worse....

It's all down hill for the credit card from here....

 

Our 2003 5.4l Exped had misfires that were not setting codes.
I took too long to figure out what was wrong and the cats clogged.
So, yes, misfiring plugs can take out the cats.

 

So there doesn't appear to be a cat after O2 sensor. How do I manage to..ahem... loose the cat? Cuz that's where I'm heading. With an Areotubine muffler.