NCT fail on CO

sirlinux

After failing the NCT on CO output (.8%) when the limit is (.3%) it's a 96 micra, im hoping it's not the cat, anyone have any ideas?

5500

Possibly some damage to the exhaust somewhere,Is the car smelling of rotten eggs or cabbage at all when idle or driving?

lomb

to pass, put on a new air filter, change the oil to fully synth (not sure why this works but it does), change the plugs, now get another appointment and b4 u go in rev the crap out of it while waiting to do the nct, disconnect the cooling fan if you have to, get the engine temperature right up there till its cooking, now reconnect the fuse for the fan and drive in, and while waiting keep the engine running whatever u do. this does 2 things, the cat or whats left of it will be HOT, this will lower the co, also the engine will be HOT, this will lower the co as the fuel will burn cleaner. also hard driving clears the injectors.
twill pass trust me, il put money on it, if it doesnt needs something else doing, ideally b4 u go in u could have the valve clearances adjusted to spec but not everyone can do this:)

Ratchet

lomb wrote:

......now get another appointment and b4 u go in rev the crap out of it while waiting to do the nct, disconnect the cooling fan if you have to, get the engine temperature right up there till its cooking, now reconnect the fuse for the fan and drive in, and while waiting keep the engine running whatever u do. this does 2 things, the cat or whats left of it will be HOT, this will lower the co, also the engine will be HOT, this will lower the co as the

You going to drive the car to NCT center and engine cat will be warm enough so just forget about pulling fan fuses and revving balls out of the car. this is the last thing you want to do 5min before NCT test.

Yeah you can replace air filter , oil , sparks
But mainly I will look at

oxygen sensor

and maybe
ignition timing
MAF sensor (but this will cause engine to run really funny)

You can always pull error codes from the ECU

lomb

Ratchet wrote:

You going to drive the car to NCT center and engine cat will be warm enough so just forget about pulling fan fuses and revving balls out of the car. this is the last thing you want to do 5min before NCT test.

Yeah you can replace air filter , oil , sparks
But mainly I will look at

oxygen sensor

and maybe
ignition timing
MAF sensor (but this will cause engine to run really funny)

You can always pull error codes from the ECU

even faulty o2 sensors start working when they are super hot.
ignition timing is fixed afaik by the cam sensor so cant b adjusted, and the maf as u say usually causes faulty running.

try my suggestion if it doesnt work il consider contributing to ur nct fund:D

JohnCleary

I had a feeling my car would fail the emmissions test for my nct so...

I took the long route to the NCT centre, via a dual carrageway! I tore up the carrage-way in 3rd ... the RPM was high... about 5k ... but it passed no problems!

I have been told by plenty of people that this works.. Not sure exactly why... Something about warming the CAT and blowing any crap out of it!

Victor

How about "go to mechanic"?

Ratchet

lomb wrote:

even faulty o2 sensors start working when they are super hot.

no they don't, they get covered with carbon and temperature doesn't help ,also some of them are are "pre heated" and they don't need much to reach operating temp

lomb wrote:

ignition timing is fixed afaik by the cam sensor so cant be adjusted,

this is done by what's called knock sensor which also goes faulty , hence ignition have to be checked as stated in nissan repair manual.


yep victor is right , just visit any garage equipped with emission testing equipment

sirlinux

cheers for all the help, checked the O2 sensor with a multimeter looks like it's seen better days. Anyway ive no way to check emissions so off to the garage me thinks.

AMurphy

Anyone capable of checking an O2 sensor with a voltmeter is certainly capable of changing same. It's pretty simple.
What mileage on the sensor?. just for reference. typical life is 60K;-30K/+60K

Heated, or not?.

However, another possibility, is your O2 sensor is correct and the problem is with teh Ig, or fuel delivery, so it is not actually stuck.... but your EFI is.

btw, what test did you do to determine the sensor was "dead".

lomb

Ratchet wrote:

no they don't, they get covered with carbon and temperature doesn't help ,also some of them are are "pre heated" and they don't need much to reach operating temp

im sure u are right, but i still maintain he has nothing to lose by gunning it, i have seen cars pass emissions when the cat is red hot.

sirlinux

AMurphy wrote:

Anyone capable of checking an O2 sensor with a voltmeter is certainly capable of changing same. It's pretty simple.
What mileage on the sensor?. just for reference. typical life is 60K;-30K/+60K

Heated, or not?.

However, another possibility, is your O2 sensor is correct and the problem is with teh Ig, or fuel delivery, so it is not actually stuck.... but your EFI is.

btw, what test did you do to determine the sensor was "dead".

It's not quite dead yet, it's taking it's time to switch from low to high and back, and it's peak voltage is quite low (.59) which suggests it's getting on, there is 110KM on the sensor and it looks like it's the original, I think ill drop it in anyway to get done, i cant test emissions, and if it's been like that a while i fear the cat might have taken some damage, though .8 isnt to badly over.

AMurphy

~70Kmls, Yes, could be getting slow to respond at tht age.
OK, just replace it and try again. CAT should be OK.

stevenmu

You could try running some fuel system cleaner through it for a week or so before hand. Also if it's carburetted, not injected, try an intensive treatment of pouring some directly into the carb while it's running (not sure if this can do any damage though so do at own risk, altough it does describe how to do it on the back of some bottles). That got me from 0.52 to 0.26.