super chevy

My '93 Silverado failed the Dallas County sniffer test Friday. My NOX levels were too high. Tech said that is usually an indication of too hot of a combustion chamber. Probable EGR failure. Might also be too lean.
I'm going back for a retest on Monday.
I've already pulled the intake off and cleaned EGR ports as well as installed a new EGR valve and EGR solenoid, and new AC spark plugs. Reset timing back to factory spec of TDC.
Anything else I can do?
Was told might be a plugged catalytic converter causing the high chamber temps.
Is my open element air filter pulling in too much air?
Any ideas?
Thanks for the help,
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XxPichulonxX

make sure u check that the TPS isn't outta wack with a voltmeter

super chevy

Will do, Pichulon.

jase

I notice that you are using a 180 stat.Would a 195 stat help you out by getting the engine to it's operating temps and burn alittle better?Just a thought to try and help you out and that might not be the problem.

super chevy

I swapped to a 195 last month when the weather got cooler.
I changed back to the stock PROM today, and taped off 3/4's of the inside of my 14x5 open element filter to reduce the airflow into the tb.
All this in hopes of passing tomorrow.
I'm not throwing any codes, so I guess if it doesn't pass tomorrow, I'll put on a new catalytic converter and try again.
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JPrevost

A functional thermostat and fan that keeps the engine below 210 and above 180 is best for getting through the Nox testing. I passed with the 330hp crate motor which doesn't have EGR. I just had to run the car with a little more fuel to keep the combustion temps down and not as much timing while keeping the car cool. The trade off is higher hydro-carbons but lower Nox. The balance was in tuning the eprom.

Fish89

I bet that you are probably running lean. But it may also be a bad cat. It is a good idea to get the car nice and hot when you take it in. When that cat is nice and hot it burns everything off better.

kevm14

Except that the 180 stat may actually reduce his NOx emissions...if the HC was nowhere near failing level, that might be a good start. Furthermore, if the HC *was* nowhere near failing level, I don't think the cat is the problem, since TBI cars NEED them to pass.

super chevy

Well, I passed yesterday....barely.
My Nox levels dropped from 1600 to 660 on the high and low speed test, while my previously very low HC's jumped to the limit - in fact, the low speed HC max is 147 and I had a reading of ... 147!
That's cutting it close!
The engine was at about 150 degrees temp when tested - helped the Nox reading, but almost got me on the Hc's.
Also, I had reconnected the vacuum line to my vAFPR for this test to get a little more fuel in there.
Thanks for the help guys.
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fast_broker

iTrader: (1)

My bet was that it was the retarding of the timing that helped you.

Make sure you remember what you did for next time...