92 350 Borderline Emissions

I just had my 92 C1500 (reg cab, step side, 350 V-8 w/ 700R4) inspected and it passed but she came real close on the NOx readings. At high idle, about 2000 RPM, she is way below standards (about half of the low idle reading) but at low Idle she is reading 981 and the limit is 990. The inspector person said that it is probably the Cat going bad and that next year it may be a problem. She's got 220,000 miles with original engine and tranny and runs great for her age.

Any opinions/ideas/suggestions/comments on what could be the culprit?

I just had my 92 C1500 (reg cab, step side, 350 V-8 w/ 700R4) inspected and it passed but she came real close on the NOx readings. At high idle, about 2000 RPM, she is way below standards (about half of the low idle reading) but at low Idle she is reading 981 and the limit is 990. The inspector person said that it is probably the Cat going bad and that next year it may be a problem. She's got 220,000 miles with original engine and tranny and runs great for her age.

Any opinions/ideas/suggestions/comments on what could be the culprit?


The blame everything on the cat.:grinyes:

Start with a good old fashion full tune up.
MT

Could also need a tune-up or the O2 sensors are going bad. It is about time for O2 sensors anyway. Have them tested.

She is in need of a tune-up at this time. How do I get the O2 sensors checked? Is this something an auto parts store can do? They are a little pricey so I don't want to change them if they don't need to be.

Get the tune up first. Then have it put on a scan tool and check the O2 sensors.

She is in need of a tune-up at this time. How do I get the O2 sensors checked? Is this something an auto parts store can do? They are a little pricey so I don't want to change them if they don't need to be.

The only thing a parts place can do is check for codes.
But remember a code does not say replace it it says check it out.
As tailight said a good scanner can read out the 02 sensors.
And for a real nittity gritty test out.
A dual or 4 channel lab scope is used.
http://www.troublecodes.net/articles/catfailure/
MT

Could be a number of things. A tune up will help a lot. With that many miles having some wear on the motor a little blow by could be another problem. Short of re-ringing the motor there is not much you can do about blow by. The tune up will probably keep you in good shape for next year. Maintenence is the best way to help out this problem.

She does have a little blow-by, it is only noticeable when I'm towing. I'm usually the one towing the Boy Scout trailer when we go camping and I've noticed that when traveling for more than 1 to 2 hours on the highway I'll get the black "soot" on the bumper (I've got a dual exhaust straight out the back). It just wipes off and is oily so I know that when the engine is under a heavy load it lets some oil get through. Daily driving there is no noticeable blow-by. I'll give her a tune-up and have the O2 sensors checked.