Can't pass CO-emissions!

[mlatten]

This is on my friend's 95 atx, w/ 120,000 miles. He bought it two years ago, and is yet to pass his emissions (he's been getting it passed by a friend who manipulates where the exhaust probe and vacuum go.)

His CO is way up, but his HC and NOx are well under the legal limits. This is different than all of the episodes i've read about, in which high CO is always accompanied by elevated HC or NOx. The tech suggested that spiking CO is due to high engine temperatures. So here's a list of things we've replaced on the car, all within the last 10,000 miles:

-o2's
-CPS
-CID
-Water pump
-ECT
-DPFE
-plugs & wires
-EGR valve
-fuel filter
-fuel rail o rings
-thermostat
-radiator
-timing belt
-New radiator fluid yesterday, with system purged
-rad cap
-probably more that I'm not thinking of right now

No vaccuum leaks found. Help.

Thanks in advance,
Matt

 

[doclees]

I have read that pulling the SPOUT plug retards the timing 10 degrees and allows it to pass. Then just put it back on for your power to return. Do a search.

 

[jedhead]

Pulling the spout will help you pass if your NOX is too high. On my SHO, my HC and CO was well below specs but my NOX was too high. I removed the spout and retested. My NOX dropped, but my HC jumped but not enough to fail. I got my Stage 1 cammed and header equipped SHO to pass CA smog with the spout pulled.

Bob

 

[mlatten]

Believe it or not, with the help of a lot of research, I was able to get my parts car to pass by pulling the SPOUT connector. The guy that inspected it couldn't believe it!

But on my friend's atx, the CO is off the charts, while the HC and NOx are way low! Could this just be a serious build up of carbon in the exhaust and heads?

Thanks,
Matt

 

[SonicRiot]

High CO is a result of incomplete burn. If it's accompanied by LOW NOx and HC's, it's a good indicator of a rich condition.

What's the fuel pressure? High fuel pressure or leaking injectors are a possibility. Run a FPR test.

How about the MAF sensor? Have you run tests on it with a multimeter? Swap it out with a known good one and see what happens.

You've ruled out ECT, but what T-Stat did you install?

You've replaced the O2s, but is the heated circuit working?

What about the spark plugs? Correct gap, probe depth into chamber, and heat range? (Are the correct plugs installed and not some hamstermarket plug?)

What are the vehicle's sensors actually reading? This info will tell you where to start. I think carbon build up may be in the wrong direction, simply because heavy carbon is often accompanied by high NOx production. Same with high temps. Often COLD combustion temps will yield high CO due to incomplete burn, but usually slightly higher HCs are seen with such a case.

Shot in the dark? MAF sensor.

 

[mlatten]

SonicRiot, thank you VERY much for the response, and everyone for that matter! I've printed out your repsonse and given it to my friend, Jim, and after work tomorrow we're getting started.

Once again, thank you.

Matt

 

[SonicRiot]

I'm curious to see how it turns out. Keep me posted.