I took a trip through the mountains over the past weekend and the Tour was REALLY down on power. Not only that, I've noticed that it's been quite a dog this summer, but I just thought it was because of the A/C being on constantly. Anyway, it's an MTX, and usually it has no problem keeping up with or passing other vehicles, even in the uphill passing lanes, but this time she was so weak that even in third gear with it floored it would not gain speed, in fact it would even start to slow down! I could also hear the engine ping sometimes around 4,000 RPM, but I was able to turn off the A/C or back off the gas a little bit and get it to stop.

Well, we got it home ok, and haven't driven it since the trip, but today I figured I should probably test it out and see how it's doing. It started up normally, idled normally, but when I tried to rev the engine it would hardly wind up at all. Took it around the block and I could floor it in first and NOT REDLINE!! It simply would not wind up that high.

I took it back home, parked it in my driveway, took it out of gear, floored it, and it would really slowly rev up to about 4500 -5000 RPM, but it would not rev higher! It's weird because it otherwise feels pretty normal except it just won't rev up, it has no upper end!

A little background is the car has 146,000 miles on it and has had a CEL for a while now, maybe a few months now, P0420 "Catalyst below efficiency threshold". Spark plugs, fuel filter, and air filter were all changed recently, and the MAF sensor was cleaned just a week ago.

I'm wondering if the cat has plugged up and isn't allowing the engine to breathe? It kind of feels like it could be an exhaust restriction. Like I said, it otherwise feels pretty normal until you try to rev it up, then it feels as if the crankshaft were trying to spin up if it were submerged in molasses or something.

I'm going to have a mechanic look at it on Friday because I do not have time for this right now, but I thought if you guys had any ideas that maybe I could zero in on the problem before I hand it over.

If it ends up being the cat, can I just gut it and use an MIL eliminator? Is gutting the Zetec cat hard to do? I noticed that the cat is built into the exhaust manifold.... that looks crazy expensive if I have to replace it!

Thanks for any advice

"I'm wondering if the cat has plugged up and isn't allowing the engine to breathe? "

Try the el cheapo plugged exhaust test.

Unplug the upper O2 sensor (to give allow the exhaust to escape). If it performs better, then you know you have a plugged catalytic converter.

mine did that for a while, the eliminator was easy to make... i had some guy gut the cat for me though... he said he just took it off and just kinda knocked apart the stuff on the inside (looks like honey comb) and banged it out... after he threw it away someone told me that some people will pay you for the old catalyst stuff.

Tony, you're the best! I've even seen you post that tip before but I forgot about it when I needed it. Thanks for the reminder! I'll go out and try to do this right now.

If it ends up being a plugged cat, do I have many options here? I noticed these aren't listed on the Team Ford site. I haven't seen many details in searches about zetec'rs gutting their cats.

Thanks again!!

One other thing could be a bad O2 sensor. Since you are removing it, you might as well test it.
Autozone for O2 sensor test

As for the other options, other than replacing, gutting a plugged cat is the only way to go.

UPDATE: OK, we're making progress guys! I pulled the 02 sensor, took it out and ran it hard through the gears.... it actually would redline now if I allowed it to!!!! It had WAYYYYYY more power than before, so I guess either my cat is clogged or the 02 is faulty? now where's my voltmeter

Another update:

For anyone reading this, especially those doing searches later on, don't be a dumbass like me and just disconnect O2 sensor and go around the block. I should have known better... the hot exhaust started trying to melt nearby fan wiring, etc. Lucky for me it didn't burn through anything, but it tried.

I would do the test in your driveway and only VERY briefly, or find some way to heat shield your underhood area in front of the open exhaust hole, then go for a drive.

Tony, it would be great if you could add this warning to your cat test for Zetec owners, just so they learn from my mistake. The upper O2 sensor hole points directly at some wire harnesses.

And for another update, I think I'm going to bite the bullet and buy a new cat for $261 from discountconverter.com so I don't have a huge possibly power robbing void in my exhaust system. Mostly I just don't want the engine to get buzzier than it already is!

Thanks again!!!

Originally posted by sk8token:

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... I should have known better... the hot exhaust started trying to melt nearby fan wiring, etc. ....I would do the test in your driveway and only VERY briefly, or find some way to heat shield your underhood area in front of the open exhaust hole, then go for a drive.

Tony, it would be great if you could add this warning to your cat test for Zetec owners, just so they learn from my mistake. The upper O2 sensor hole points directly at some wire harnesses.
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I learn something new everyday.