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All guesses welcome, plugged cats

2008 Ford Expedition 5.4l 3valve

Bought used 10/10/2009 with 39894 miles.

- at 44776 miles left side cat converter plugging up, cel light on, ordered parts under warranty kept driving truck waiting for parts.

- 2 days later cel light back on, bucking and missing, parked truck till parts came in ( ordered both sides to be sure ).

- after cats installed asked Ford techs what may have caused it, they performed an injector flow test to see if running too much raw fuel…passed test.

- no new theories only guesses ; bad fuel supply ( I get gas at the same Conoco station each time ), heavy acceleration ?



- guesses anyone ?

Why do cats plug up on a truck with only 44k and no previous symptoms ?

What do I do to prevent this in the future ?

I’ve got two guesses:

  1. bad luck - ? Sometimes parts aren’t up to snuff, make it through quality control and you’re lucky enough to end up with the results of someone else’s hangover or whatever.

  2. unfortunately you apparently have almost 40K miles unaccounted for. Maybe the prior owner had a rich running condition and ignored it. OR - maybe the previous owner was a fuel additive junkie. I have no authoritative info about this, but have seen the claim that too much of certain kinds of fuel additives can wreck a cat.

Buying used may be the key. someone slammed 40k on this truck in 19 months in the Phoenix area.
There are cautions against using fuel addditives containing metalic compounds like manganese so one would really have to read labels if using such. Oh, and you’d also have to read the owner’s manual to see this caution…did they ?

And so remains the unanswered, or is it un-answerable questions.
What caused it and is that a preventable situation ?

Operating temp or time ? ( one mile to work for me, INCLUDING the detour to get the kids to school. )

I suspect the problem was caused by what the former owner put in the gas tank. Maybe someone told him he could use 50% fry oil…We see some pretty strange posts on this board about fuel and people trying to “save money”…

In your case I would change the four oxygen sensors too, as these parts are what controls the fuel mixture and protect the converters…

You know this vehicle was probably a repo or abandoned lease…

When my cat got plugged I’d put mineral oil on her tummy fur to lick off.
(Sorry, couldn’t resist.)

Are you sure the cats were plugged up or were they replaced due to converter codes?
Cats usually clog up (IF this is the case) due to excessive rich running or oil consumption over an extended period of time)
It’s possible that if clogging existed it could be caused by something added to the gasoline. (say regular doses of unneeded, certain types of additives)

They did warranty this didn’t they? Cats are covered under the 8 years/80k miles Federal emissions warranty.

Yes , warranty.
Left side visually restricted and threw the first code. Then broke apart internally and parked the truck.
Right side has a few clogs.

An engine misfire, if ignored, will overheat the cats and cause them to fuse/melt and destroy themselves…At highway speeds, this process can take place in 15 minutes or less…Since you bought this vehicle used, you don’t know its history…All you can do is replace them and hope for the best…

Did you use up a supply of older oil with a high level of ZDDP in it? This additive contains phosphorous (known as converter poison)? Or did you use a high phosphoros additive?

I am reading some tech material that implies converters have gone to a 10year 100K OEM warranty, anyone heard anything?

Don’t know that kind of history on this truck.
When it came to our dealer we prepped it with our Motorcraft 5w20 synth blend, and after the converter replacement we changed the oil again with Motorcraft 5w20 blend.

I’d have to think the converter problem was caused by something in the past related to a severe engine ignition miss that was left unattended for a while or an excess of fuel being dumped into the engine. (leaking fuel pressure regulator, injectors losing grounds, even intermittently, and remaining open (very rich running), chronic use of an oddball additive, or possible someone in the past overfilling the oil by quite a bit. The latter could force oil into the combustion chambers and it doesn’t take much of this to cake up a converter.

Just theories anyway. There’s no way of being definitive at this point but I believe it was more of an owner error than a manufacturing fault.