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I have a 93 civic coupe with a d16z6 and I can't pass emissions. I just bought the car for 300 from a friend and the only thing that was wrong with it tps and I replaced that. It ran hc .72 out of 1.00 the NOX ran 1.20 out of 2.50 and my CO ran 12.12 out of 12.00. I'm lost on what could be causing this.. The motor has been rebuilt about 50 thousand miles ago and I have all the receipts for the rebuild. I've put new cap, rotor, dizzy, wires, plugs, and the cat was replaced about 8 months ago. I was told that running denatured alcohol would make the car run cleaner and i have used it in my 73 dart and it does help but on this car it made it worse. It brought my HG to .92, CO raised to 12.90 and nox went to 1.32.... I'm new to the honda game and would appreciate any help! If you need any more info please ask.
 

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I did both times. I went to the emissions testing about 25 minutes from me. I sprayed carb cleaner everywhere and the idle didn't spike. But when I put it in park after driving it for a bit the idle jumps around for a few seconds then files normally. Also while I had the hood popped I noticed it sounded like the motor was sucking a lot of air almost a whistle of sorts.
 

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Okay so you are failing on CO, high CO emissions is from incomplete combustion.

Check air filter (replace if dirty)
Check the PCV system (replace the PCV, its cheap so why not?)
Check the EVAP system (canister is probably full of fuel from over filling the tank, obviously replace or delete if so)
Check the o2 (during normal operation an oxygen sensors voltage should be switching between 0.1 to 1.0 volt at a rate of approximately 50 cycles per minute)

Uncommon
Check TPS voltage (.4-.5v closed to 5ish v open)
Defective MAP and/or ECT
 

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Check all grounds.

Verify O2 sensor is less than 5 years old or so. If it was in there before engine build, take it out and clean it with mineral spirits and a toothbrush. Bits of metal from the rebuild could have blocked part of the sensor.

Buy a cheap set of injectors, then send all 8 to Injector Clinic to get cleaned and matched.

Make sure fuel pressure regulator is in good condition.

Or just skip all this, buy an adjustable fuel pressure regulator, and turn the pressure down SLIGHTLY
 

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Discussion Starter #7
How do I check if the fiel pressure regulator is in good condition or not? And the o2 sensor is a New boshe I put on when my friend owned the car. Air filter is new as well just some cheap spectre air filter. I'll have to check the charcoal canister. Could the timing be an issue in this as well? I can't set the timing on it right because someone took the lower timing belt cover off and lost it.
 
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