Emissions Trouble

The cats need to be on and working to pass, that is your main problem. I have a 93 5.0, 70mm and 30# and 8# blower and just passed with super clean emmissions. Your timing is OK, stock is 10. After fixing the cats, check/fix all vaccume leaks, check at the charcoal canaster on passengersid enginebay way up front on the frame, there is a rubber elbow that loosens up and comes off. after fixing that stuff, and still dont pass you can go get it tuned, by a tuner.

" off-road H-pipe, " Well duhhh....

No, that's the funny thing - there's a separate checkbox for catalytic converters, and THAT passed. The test that failed was the sniffer test. Would no cats definitely cause that? When I heard the HC and CO tests failed, my immediate thought was that it's running rich, but I'm thinking maybe those @#%$@ cats actually do something... Also, am I right that the air tube is part of the EGR system? Next, like Chumley suggested, I'll need to get the whole car vacuum system checked. Every Fox - body I've worked with had vacuum troubles, and that's a job I'd rather pay a pro to do. Those hoses seem to get brittle and crack...

ya, they burn off the bad gasses, they are at about 500 degrees and need extra O2 from the air pump to do it. there was a recall on the cats for 89 (?) and before a while back the matrix inside could loosen and get sideways rattle etc.

yes, supplies more O2 to burn........

there is some guy selling kits of silicon vacuumed hoses for older mustangs on Ebay.

Do the cats actually do stuff? Now, that's an odd question.... Of course they do stuff and that is why they were installed.... Read this

If the car has a vacuum leak, this can upset the mixture control at idle (providing the car is going in to closed loop)... moreso on a car with a MAF.

The air tube as part of the EGR? If we are talking about the air tube to the cats, this tube supplies air to the cats in order to light them off.... Once things are up to temp, this air is usually diverted to the exhaust manifolds to help reduce HC and CO...

Since it sounds like the car is without cats, it is surprising that it would pass the visual....

No Cats will not cause you to fail your sniff test. I have a 460 with hollow cat, passes with flying colors every year.

OK, is this a troll??? The check box is probably the visual inspection that they are there, and they probably didn't look. Of course the cats DO something or they wouldn't be required.

Thank you to everyone who pitched in their .02. I took the car to a local speed shop. (I don't want to spam the group, but they are in southeastern PA, they do good work, and they seem to specialize in Mustangs. Let me know if you want more info. If they do good work, I'm happy to refer people.)

Anyway, they (custom) cut in Magnaflow hi-flow cats, installed headers (an added bonus - not required), and they re-connected the air tube. It was a little expensive, but I passed the sniffer with flying colors

- like new-car clean!!!!

For what it's worth, before this round of work, the exhaust was stock headers, off-road H-pipe, and single chamber Flowmasters, with all piping after the headers 2 1/2". After, it's BBK shorty unequal headers, hi-flow Magnaflow cats and the same single chamber Flowmasters, all still in 2 1/2" piping. The results, besides a legal emissions test? The car got much quieter - it was loud to the point of rudeness before, with more of a controlled, almost tuned exhaust note; the power band seems to have shifted upward by 500 - 1000 rpm, and the performance is mildly noticeably increased.

Thanks again for all your input, I wanted to post the end of the story since so many people chipped in.