$20 on a used cat in Sweden???? Send all you can to me. Our scrap yards pay lots more......

Amen Brother!
Around here, guys & gals go out to their cars/trucks in the morning to find that some low-life CUT THE CAT OUT AND SOLD IT to crooked scrap dealers. <img src="/forums/images/graemlins/ignore.gif" alt="" />

If you can find a stock one that is still good, pick it up for the $20, chances are by the next test the new one wont be working as well.

I put a hi-flow magnaflow on my truck in '04 after I rebuilt the top end. It past in '05, but the HC's & CO were much higher than any test in the past. In '07 it failed the first attempt for idle, everything else was fine, adjusted the idle and it barely passed. This month it failed again, not the HC's but the CO was .05 too high. I put the old oem cat back that had been sitting outside exposed to the elements four 4yrs on and retested it, and it passed w/o issue. The CO was 70% less, and the HC's were 45% less.

I'm hoping for a life time of atleast a couple of years on this cheap one. The OEM probably cost 10 times as much, ofcourse they hold 10 times longer but it feels expensive to put out that much money at once. Probably better in the long run...but I'm a cheap bastard!

Still got the old one? Did it run OK before you swapped it out? If so, you could put the old one back in, then just put in the new one to get you thru emissions next time. Not that I would do it, but just a thought.

Now that the test is done and passed, a state EPA ramp checker would have a coronary right on the spot if he/she would look under the hood and chassis of this truck I know.
Headers, no smog pump, a bored-out cat. Wonder what mpg he gets? I'll ask him in a few months.

I meant picking up a used oem one from a yard.

I did a little comparison between the oem one I have and the Magnaflow one. The catalyzing chamber of the oem one is 3.75 times larger(245 cubic inches to 65.625 cubic inches) than that of the Magnaflow, even though the oem one only looks like it is twice the size(it is twice the weight.

Here is a pic, the "X" is the size of the catalyzing chamber from screen to screen.


I think the hi-flow cats operate at the edge of efficiency in favor of performance.

I haven't measured the size of the catalyzing chamber on a standard after market replacement yet, but I know they are a lot lighter, and is why they don't last as long.

By law in the US, OEM smog parts carry a very long warranty (75K miles sticks in my mind, but not sure), so they over-engineer them to last even longer than needed.

Better for the car company to charge the buyer a lot for a better cat than it is to have to replace a bunch for free.

Dave

Well the problems continues...
the emissions test I took last weekend wasn't official and I went for the real one today and flunked again!!!
HC around 400-500, the others were good.
So I'm back were I started except I know it's not the cat that's the problem, except maybe it burns out really quickly because of the unburned fuel passing.

So what can cause unburnt fuel passing through to the exhaust?

If I read correctly you have done:
Tune-up and valve adjustment
Checked for vacuum leaks
fairly new O2 sensor
new cat.

The only other things could be timing, leaking injectors, leaking cold start injector, it could be the cam but I am not sure.

When you tightened up the exhaust manifold and down pipe connection, did you replace the gasket, or just tighten it up? You could still have a small exhaust leak that is allowing fresh air to be drawn into the exhaust and causing the O2 read lean and the ecu is richening the mixture.

Is it failing at both stages of the test, idle and highway rpm's?