Direction of catalytic converter on 95-97 Tacoma 4WD?

If anyone owns a 1995-1997 Tacoma 4WD 2.7L regular cab with the original Toyota catalytic converter, please keep reading. This may apply to later years also. These are the short 4WD trucks with a single cat vs. Xtra cabs which apparently have two.

Look underneath the truck where the cat is installed above the cross-member on the passenger side. There are rows of ventilation holes on the bottom of the cat. At one end, there should be a single ventilation hole in the center in its own final row. I'm trying to find out whether that hole is on the muffler (outlet) side or engine (intake) side of the cat, as properly installed. I'm not sure if they all have that feature but it makes a quick reference.

These cats are also asymmetrical in that one end has a longer expanse of "unbent" sheet metal with longer stiffener ribs. The gaskets at each end are the same, which is confusing if you have no reference to the old one (long story).

The factory manual has a weak diagram, with reference to a "delta mark" at the intake end; absent on the factory replacement. It seems many of these factory cats are poorly marked for directionality. The cat needs to be installed in the right direction because two chemical reactions augment each other. It affects emissions but is negligible to flow.

Thanks for any help, especially if you can post a photo somewhere.

Vic

Reply to
Vic
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I'm confused.

One, I was not aware that a CAT was directional, I thought it worked the same no matter which end the exhaust gasses entered through.

Two, the drain holes go on the bottom.

Three, you said it was asymetrical, this means to me that it only fits one way because if you put it in backwards, the asymetrical-quality of the device would cause it to strike stuff.

Four, if it really cared what direction the gas was going, it would have an arrow stamped on it to indicate what it wants to see in terms of airflow.

Reply to
Jeff Strickland

"Jeff Strickland" wrote in news:MOKsi.27$vK2.13@trnddc03:

See:

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A TWC (most common type) is definitely directional. You have to read the details of the reaction sequence. I have a feeling many cats are installed backwards by people who didn't bother.

Some people still think they are a conspiracy to rob power (clean air is optional?) But they have become much more free-flowing than the early models. Old timers' tales die slowly.

Yes, that went without saying!

The shape is mildly asymmetrical only at the ends before the flanges. Not enough to hit anything. The original was already replaced with a cheap (burnt out) model so there's no reference. Looking covertly underneath two similar Tacomas, it looks like the end with the longer unshielded stretch of metal faces the muffler, assuming those are factory originals not installed backwards. The only mark on my new one is green and blue paint on the long end; could be a number of things, like a QC mark.

I tried to state why that wasn't obvious. A local service dept. also gave conflicting advice. Does anyone have the same truck who can take a look or a photo? Thanks.

Vic

Reply to
Vic

I found this on eBay, I hope it helps ...

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It shows that the O2 Sensor hole goes on the outlet end of the CAT.

That's a huge "DUH!" We shoulda known that ...

Reply to
Jeff Strickland

"Jeff Strickland" wrote in news:AG2ti.237$MT3.10@trnddc05:

Good catch, but that eBay unit isn't an original Toyota cat. It has no protrusion like that, but there is a punch-out circle hidden inside beneath the outer shield. You'd have to drill another hole to make it useful. I ended up installing it in that same direction based on visuals from other trucks. Why they can't put a simple arrow on it is beyond me.

Vic

Reply to
Vic

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