Trying to Pass DEQ! 85' 720 CO levels too high

[djmikemouse]

I'll start off by saying I've got an '85 Nissan w/ king cab and long bed. Runs on gas and we just passed 200,000 miles about 100 ago. I went to DEQ twice today. The first time my CO levels were 1.1942 and 1.3625, passing is 1. After the fail I came home, and replaced the air filter and went back. On the 2nd test my CO levels were 1.0663 and 1.6172. I do not have a tachometer so I belive that I got the rpms too high before the 2nd idle on my 2nd trip to DEQ. I read on another post that messing with the idle and fuel mixture settings but I am not sure how to do this or what I'm actually trying to achieve to know that I'm heading in the right direction. Good thing I procrastinated and have 1 day left before my tags expire. Any help would be much apreciated!

[djmikemouse]

One thing I forgot to mention is that once I let off the gas pedal the truck still accelerates for about 2 seconds before rpms start to drop. Even in idle I can tap the gas real quick and the rpms will continue to rise after I depress the pedal. This is probably part of my problem but I have passed DEQ with this issue before.

[datsunaholic]

'85 won't have an adjustable idle mix if the carb is original, as it's a feedback carb that uses an O2 sensor.  If all other emissions levels are normal, it may just be time for a new catalytic converter.  My '81 510 failed with almost double the CO readings and a new cat alone dropped it to half the allowable.  The old cat was entirely collapsed inside on mine, though.  While your numbers seem "close" to passing, they're actually quite high as that engine should be well under 1%.  Factory manual says 0.3%.  The other part that lowers the CO levels is the Air Induction System.  If the AIS valve is stuck, it can cause high CO numbers.

 

The idle delay could be sticky linkage- try operating the throttle by hand and see if the delay happens when you force the lever back to idle.  Normally though the DEQ station won't pass you if the idle is too high anyway.

[djmikemouse]

Would adjusting the throttle or the idle screws do anything? As much as I would love to replace the cat I need to do something right now to pass DEQ and I unfortunately do not have the time to replace the cat. I appreciate the reply man!

[datzenmike]

Do you have one or two wing nuts holding the air filter on?

 

Two is throttle body EFI after April '85

One is a carb

 

All California carbs are electronic feedback with O₂ sensor and a solenoid primary jet. There are 6 wires to the carb harness.

Federal (non California) carbs only have two wires and the idle mixture screw is set and sealed (non adjustable) from the factory.

 

Before the test make sure the engine is hot. A stuck thermostat and a cool running engine will have higher HO levels.

 

Is your choke fully open? The choke is a mechanical device to make the mixture richer

 

Are your plugs clean and are both sides (intake and exhaust) firing?

 

The front of the carb has a small round glass window. Is the fuel level... level with the DOT on the glass? Too high and the carb may be flooding and raising the CO levels.

[Draker]

High CO can be caused by an exhaust restriction as well.

[djmikemouse]

There is one random wing nut on the air filter, I don't belive it is stock. I will be able to check everything else tomorrow. Thank you!

[datzenmike]

One wing nut in the center?

 

Carb then.

 

Do you have an oxygen sensor in the exhaust manifold. Green wire to it?

[djmikemouse]

I was able to pass deq! But I'm not sure where the exhaust manifold would be

[datzenmike]

Well if you passed it doesn't matter where the exhaust manifold is.

 

 

What did you do to get it to pass????