94 q45 wont pass emissions

[tporter]

i have a 94 q45 that will not pass inspection the hydrocarbons (HC) readings are 1.6683 gpm the readings needed to pass are 0.9000 gpm carbon monoxide (CO) readings are 30.3616 gpm and 20.0000 gpm to passthe only thing that passed was oxides of nitrogen which was 1.0758 gpm and 2.100 gpm to pass what could cause these readings to be off. thanks in advance TP

[maxnix]

Could you please state your maintenance history?

Have you ohm tested your knock sensors?

When were O2 sensors last replaced and what was the brand if not Nissan or NTK?

You might want to search on similar threads in Infiniti Online Mechanic.
Modified by maxnix at 5:53 PM 3/4/2009

[Infinitiguy19]

I am not 100% on my answer but are the Cats OEM?

Is the check engine light on?

Any maintenance on the EGR valve?

Are you running rich (Black some from the tail pipe sometimes)?

Welcome to NICO.

[Q45tech]

I would read MAF voltage at idle and cruise to make sure it conforms, same with injector open times vs rpm and load, then test cat temperatures [IR gun] or drop exhaust and physically examine them.

94 cats are less robust than 90-93 cats due to differences in metals plated on comb to decrease emissions [94 more stringent than 90-93]

[tporter]

yes it does black smoke sometimes if i hit the gas pedal real hard as if its blowing it out then it doesnt do it anymore

[maxnix]

yes it does black smoke sometimes if i hit the gas pedal real hard as if its blowing it out then it doesnt do it anymore

Like right after it upshifts and you release the accelerator pedal somewhat?

So tell us about OCI, oil brand and filter. And any other maintenance as asked before, please.

[goody90q45]

When were O2 sensors last replaced and what was the brand if not Nissan or NTK?

To the OP- What's your mileage? Have the O2 sensors ever been replaced? It's probably time.