Smog check help needed

Kejtar · Jan 19, 2006

NO (ppm) 713 @ 15mph failed
NO (ppm) 684 @ 25 mph (barely passed)

Everything else passed. I have found refernces to bad cat and needing to run fuel injector cleaner.

Info on the vehicle: 94 4.0 HO at about 190K miles, got it in Nov, been sitting probably at least since August.

5-90 · Jan 19, 2006

Clean the fuel system, and it might not hurt to spray a light water fog down the airtube on a high idle (Dx the cat if/when you do.)

Not only does fuel turn to varnish when it sits for a while, but you might have some carbon that's gotten a good hold in your chambers. Since you don't mention any other failures, the high NOx is going to be largely due to elevated combustion temperatures - and they're probably not getting corrected by the cat. If you do the "water trick," (I've posted instructions before, and I can PM you them if you don't find them anywhere,) do it BEFORE you change your cat, because the carbon that's likely to be loosened up will find its way down the exhaust pipe, and end up coating the converter matrix.

5-90

Kejtar · Jan 19, 2006

5-90 said:
Clean the fuel system, and it might not hurt to spray a light water fog down the airtube on a high idle (Dx the cat if/when you do.)

Not only does fuel turn to varnish when it sits for a while, but you might have some carbon that's gotten a good hold in your chambers. Since you don't mention any other failures, the high NOx is going to be largely due to elevated combustion temperatures - and they're probably not getting corrected by the cat. If you do the "water trick," (I've posted instructions before, and I can PM you them if you don't find them anywhere,) do it BEFORE you change your cat, because the carbon that's likely to be loosened up will find its way down the exhaust pipe, and end up coating the converter matrix.

5-90

I remember reading about the water trick but but I couldnt' find it now (I searched for quite a while and came up with some interesting results

)
Anyways I'd appreicate the info on the water trick.

5-90 · Jan 19, 2006

I'll be running around to-day, and I've got a couple stereos to install. Please, PM me a reminder, and I'll get it to you withing 24-36 hours.

5-90

casm · Jan 19, 2006

Yep, high NOx is usually caused by cat failure - every vehicle I've had that failed with high NOx was exactly that. I'm willing to bet that if you replace it with a generic you'll pass.

5-90's suggestion of cleaning the intake is a good one, though, and I'd also recommend hitting the fuel system while you're at it. Just be sure to NOT go back for the re-test with any additives in your fuel; they can cause a failure depending on what's been added and what it's cleaning out.

What I usually do before smog is clean out the fuel system and intake, then let a half-tank of 'pure' gas wash through before taking the test (or retest as the case may be). At least this way I can eliminate bad or tainted fuel as being part of the problem.

Smog check help needed

Kejtar

PostMaster General

5-90

NAXJA Forum User

Kejtar

PostMaster General

5-90

NAXJA Forum User

casm

NAXJA Forum User

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