Ok I recently had MAC mids, a magnaflow universal high flow cat and a slp loudmouth 1 exhaust just put on my 95 z28. I went to go pass emissions and this is what the results are
High Speed Test
Standard Current reading
HC(ppm) 114 147 failed
Co% .63 .34 Passed
CO2 n/a n/a
02% n/a n/a
Nox(ppm) 796 1326 failed
Dilution >6.0 14.74 Passed

Low Speed Test
HC(ppm) 117 185 failed
Co% .65 .41 Passed
CO2 n/a n/a
02% n/a n/a
Nox(ppm) 879 1651 failed
Dilution >6.0 14.71 Passed


Any help on how to fix this would be great.
Wes

 

Failing for both HC and NOx would seem to point to the cat. If it was running rich, HC and CO would be high, and NOx would be low. If it was running lean, NOx would be high, and HC and CO low.

 

he said i may need an injector cleaning and a lower grade gas. Do you think that would help me pass the test? The cat is brand new but it is a high flow cats.

 

I failed HC and NOx on my car pretty bad (2.5 allowed NOX and i had 2,7 and .8 HC allowed and i had 1.5) it turned out to be the intake elbow.... it had a crack and was getting unmetered air into the system and the computer was overcompensating for it by throwing too much fuel creating a rich condition... im being dead serious... an oil change and a new elbow and my numbers dropped from 2.7 and 1.5 to .30 and .13

 

Well I probably need a oil change but I'm sure my intake elbow is in good shape. I guess I'll try getting an il change and a tune and see if that works.

 

Could be as simple as a lazy O2 if they have not been changed out in the last 50k miles with AC Delcos. Get a scan tool and see if the O2s are active at idle. or lazy and slow to change. Also check to see what the BLMs are reading at idle and cruise speed of 25mph where the TX test is done.

 

Ok call me stupid but where do I get it scanned and whats blm?

 

BLMs are your Long Term integrators...have to have a scan tool to understand their usfulness in tuning, but basically, if they are at 128, then the O2s are reporting a perfect air/fuel ratio..anything higher its lean and the computer is adding fuel, anything under and its rich and its cutting fuel. If they are too far off of 128, say more than 10-15, then thats a very good possibility why it failed..the further you get away from the "perfect" afr, the more inaccurrate the O2 reading is and it begins guessing basically how much fuel to add or cut to make it "perfect" again.
A scan tool is invaluable with an EFI car of any kind, can get laptop versions, or standalone hand held units, just search for them and you'll find tons of info.