imp

'94 GT 5.0L HO 5-speed, 164k, most everything original still there, all operable. Very poor fuel economy, stinks like hell at idle, O2 sensors have a light black soot appearance. Before anything else: I have a brand new identical engine bought from Ford when they were discontinued, around '95-'96; Ford sold the inventory for several years. From that new one, I took:
injectors, throttle body, distributor with new TFI, wires, plugs.
Replaced PCM with a rebuild. Set at 10 degrees BTDC with jumper removed. Timing light shows good advance upon throttle-up. Installed adjustable fuel pressure regulator, set at 35-40 psi. O2 sensors are new.

Decided it was the cats, possibly restricting flow. Yanked down the H-Pipe, inside looks black rather than tan/brown at inlet. Today, I cut out one cat, to have a look-see inside. Here's what I found:

The cat removed:



The cat standing upright:



View through the cat with no illumination:



View through the cat with a flashlight sitting at the other end:



Long ago, I cut open a cat, off my Fiesta. It had a square-tubed structure running clear through it, the squares about the size of window-screen openings. You could barely see a bright light shone through them. Has internal catalyst placement changed, situated along the inside walls only? There is a narrowed down passage, but wide open, halfway through, cross-section big as a playing card. Edge of that opening is visible above, inside.

What in the hell do I have here? Fake cats? Is there such a thing? The big rear mufflers are still marked Ford with part numbers. Obviously, what I have AIN'T restricting flow........

Anyone knowledgeable about cats, help will be appreciated! Thanks! imp

EDIT: Should have mentioned, engine runs just fine, idle quality amazing for the miles, plenty of power, very smooth tip-in and tip-out, can say nothing bad about how it runs.

08'MustangDude

Who ever had it before you gut the cats, or jammed a straight pipe through them. Old trick, and
in certain counties in PA, you can still get away with it, since those certain counties do not have
emissions testing. However, they are supposed to do a visual, and make sure the cats are there.
They can't take them off and look, so, people gut them.

The stink at idle, good old fuel, like the days before CATs were used...

Black is simple carbon build up, and without the cats, it doesn't get hot enough to burn a lot of
it out.

ZEN357

If the smell really isn't that bad and you don't have emission testing, I'd put them back on and run it that way or put a straight pipe through them and then put them back on. I always hated the catalytic converters. I once had a 1987 Fiero GT with a V-6 and a 5-Speed, I put a Hypertech 160 thermo and stage 2 chips in it with an MSD box on it, that alone made a great difference, but when I replaced the cat with a gutted one, I ended up getting and I am not joking between 28 and 30 mph if I stayed off the gas pedal.

imp

I thank you for this. The inside looks made that way, the as-fabricated wall of the outer wrap still has tool-roll marks from forming, no through-pipe, it is virtually wide-open.

So, still no idea on fuel consumption, really. imp

imp

As I mentioned elsewhere, my two pet projects, '70 Bronco w/5.0 HO and T-5 never did less than 20- mpg with 3.50 gears. '79 Ranchero same except AOD, got 25 on highway, unbelievable for the big boat, had 3.10 gears. Neither had cats, both used early '90s EEC-IV with 2 O2 sensors. imp

08'MustangDude

Yep, you can buy them:

imp

You're very knowledgeable. You may know this already, but if not, Ford Mustang Shop Manual calls the smaller front cats "Conventional Oxidation Catalysts" (COC) explaining that they only affect HC and CO emissions, and are sometimes called "Two Way Cats". The larger rear cats are known as "Three-Way Catalysts" (TWC), since they affect HC, CO, and NOx emissions. So, if Emissions Test measures only HC and CO, as early on they did for me, in Phoenix, NOx was no worry. Then came the dynamometer testing, which was called something like "240 something or other", because it ran up the engine under dynamic loading, maybe for 240 seconds, or some such nonsense.

My present location, Mohave County (AZ) has no emissions facility at all. I face no test, regardless of vehicle. I AM interested in the environment, however, am glad I don't fight California's smog (or anyplace else's), but would at the same time like to secure the kind of performance I got from the conversions I did, and the previous 3 Fox Mustangs we drove, '89, '90, and '93 Cobra, all 5,0s. imp

imp

FWIW, today I welded the one cat back into the H-pipe which I had removed to inspect inside. Long while since I MIG-welded, but acceptable, by my standards.

08'MustangDude

In some cases, having those pass-through cats, will hurt performance, there is no
back pressure for low end torque. You should at least have the three-way.

The front two-way, a minimum exhaust temperature of about 200°C is necessary for the
catalysts to “light-off”; 426 °C to efficiently convert harmful exhaust gases into inert gases,

A 2-way (or "oxidation", sometimes called an "oxi-cat") catalytic converter has two simultaneous tasks:
Oxidation of carbon monoxide to carbon dioxide: 2 CO + O2 → 2 CO2
Oxidation of hydrocarbons (unburnt and partially burned fuel) to carbon dioxide and water:
CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O (a combustion reaction)

Three-way catalytic converters (TWC) have the additional advantage of controlling the emission of
nitric oxide (NO) and nitrogen dioxide (NO2) (both together abbreviated with NOx), not to be confused
with nitrous oxide (N2O).

imp

Very worthwhile info!

"nitrous oxide (N2O)." Ha, Ha!!

imp