NEED EMISSIONS HELP

HI,I OWN A 2 WHEEL DRIVE 95 CHEVY TRUCK WITH A 305 WITH 149,000 MILES ON IT AND I HAVE TRIED TO PASS AN EMISSIONS TEST 3 TIMES NOW AND IT IS STILL FAILING AND I NEED SOME HELP FIGURING OUT WHATS GOING ON.THE TRUCK RUNS
GREAT AT ALL SPEEDS AND DOESNT INDICATE ANY PROBLEM FROM A DRIVABILITY STAND POINT BUT IT BOMBS ON THE HC's AND THE Nox.HERE ARE THE ACTUAL RESULTS FROM MY LAST INSPECTION ATTEMPT.
HIGH SPEED EMISSION RESULTS (25 mph) -------------STANDARD---------------CURRENT READING HC(PPM)--------143-----------------149 FAIL CO(%)----------1.60----------------0.70 PASS CO2(%)---------13.8 O2(%)-----------0.6 Nox(PPM)--------905----------------1572 FAIL DILUTION-------->6.0---------------14.5 PASS
LOW SPEED EMISSIONS RESULTS (15 mph) ------------STANDARD-----------------CURRENT READING HC(PPM)--------147-------------------152 FAIL CO(%)---------1.24------------------0.57 PASS CO2(%)---------14.0 O2(%)-----------0.5 Nox(PPM)--------990-----------------1537 FAIL DILUTION------->6.0-----------------14.57 PASS
ANY HELP WOULD BE GREATLY APPRECIATED,BY THE WAY I HAVE REPLACED THE EGR AND THE O2 SENSOR ALSO THE THROTTLE BODY BASE PLATE GASKET.THANKS
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Hope this helps.... Immediately prior to taking the vehicle in for testing:
Replace PCV valve, change your oil filter and oil, new air filter and it should pass. Also, make sure ypur plugs/ wires are in good shape (good spark=good burn).
One other thing...are you in Ohio?
T.
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THANKS FOR THE HELP TERRY ,IM IN HOUSTON TEXAS.BY THE WAY I HAVE HAD SEVERAL PEOPLE TELL ME ITS THE CAT,COULD THE CAT CAUSE MY PROBLEM?
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Might very well be, I just read thru the report a little more and the high NOx count might indicate a catalytic conver that has lost it 's effectiveness...pricey, but the other things I listed are always a good starting point...
Curious about Ohio as we have only certain counties with e-check and some are a little more tolerant than others.
T
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wrote:

Yes, it could be the cat... but when was the last time you checked your cooling system? I had a 305 that had *strictly* high NOx values, and poor cooling... one rebuilt water pump later, the NOx is nearly zero.
Just my 2 cents.
V Vuarra
Quid quid latine dictum sit altum videtur. (That which is said in Latin sounds profound.)
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THANKS GUYS FOR YOUR INPUT,IM GOING TO START WITH THE CHEAP STUFF FIRST AND GO WITH A NEW CAT AS A LAST RESORT.I REALLY APPRECIATE YOUR HELP,
ROBERT FROM TEXAS
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Just remove air filter and let it breathe a little easier and pump up the tires to 40 lbs and that helps relieve some of the problems right off the start.

IT
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