carbon monoxide goes up and down drasticly! help!

[nastynissan]

my 1990 240sx wont pass smog due to carbon monoxide going from 0% up to as high as 7.5% UNDER A LOAD ONLY, at idle it is fine, i got a new cat, o2 sensor, i have tried a lot of differant combinations to figure it out, but i cant! everything else is fine... the car doesnt change in rpm, or sound differant, it just shows up on the dino..... i dont get the best gas milage either!

[180fan]

so when was the last time you had given your car a tune up?

[nastynissan]

ive done everything but the oil change, but im doin it tomarro. but i dont think that would matter too much in this situation. the car runs excelant. its just the unsteady co levels... please help with any information i can use though..

[DevilMB3017]

Stuck EGR vavle? Try cleaning it out.

Edit: There has been a thread around here about how to do, but I can't find it atm...

[nastynissan]

tried and checked, any other posibilities? im stumped! even my nissan crew cant figure it out.

[nastynissan]

my ka24e wont pass emissions due to carbon monoxide going up really high, and then down to 0. had a tune up, and only 97k on motor. bought a new cat, and o2 sensor.. please help. i cant afford to drive my 8mpg truck everywhere.. thanks

[180fan]

High CO = too much fuel. Your other numbers should reflect this as well (well not NOx, or not really).

[nastynissan]

yes, true. all i need to figure out is what controls the air to fuel ratio, because i think its kind of actin like it is slow at resonding to the sensors or somthing. the co idles at 0%, but you put in 1st and you have the problem showing on the dino. like this. .> 0%,,2.4%,,7.5%,, then down again,2.?,,1.?,,then 0%.. then it continues the pattern..... help... i need it..

[rogoman]

Test the temperature sensor that's used for the ECU; if it's bad, the ECU will provide a much richer mixture.

[nastynissan]

will it go rich to lean? we hooked up a scanner a while back and it said the temp sensor was bad, but i replaced it, off a spare engine.. could it be giving a weak signal?

[180fan]

that little harness that connects to it could also be corroded at the plugs as well. You may want to spritz some electronics cleaner and tighten down those female plugs.