High NO only at 15mph

[Cabriolet]

so my friend's car didnt pass smog the first round. so she had me change out the broken intake stuff. i put on: a new icv hose, new spark plugs, cleaned the icv, new intake boot, new valve cover breather hose and fpr to intake hose. and she just barely pass the 15mph.

any ideas on why only at the 15mph the NO is so high? but it's perfect at 25mph?

also the rest of her numbers are just fine, which makes me think it isnt the cat at all.

sorry the car is a 1991 325ic real mtech automatic

[Cabriolet]

Jim?

[jlevie]

HC and NOX are both high at 15mph and more normal at 25mph. Which makes me first think of intake leaks that are causing a lean condition and partial misfires. A smoke test is the only way to tell if there are leaks.

[Cabriolet]

ya that's what i thought. i didnt check the intake mainfold gaskets or the break booster.

also, would a dying AFM cause similar issues?

[bastianshaw]

exhaust leaks pre cat wil cause lean

[bastianshaw]

maybe dying fuel pump or clogged filter or injectors

[bastianshaw]

also why do u care if it passed?

[Cabriolet]

because i work on her car for her and want to make sure it's running perfectly. i may try to buy it from her in a few years. it a red mtech2