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Discussion Starter #1
Hi everybody,
Ok so in order to get new insurance and plates here in Ontario, I need to have the car safetied and tested for emissions. So it passed the safety, but not the emissions. the three ares it failed in are called HC ppm, CO % and NO ppm. The results were HC ppm 247(limit is 75), CO % 1.58(limit is .42) and NO ppm 2503(limit is 0864). I was floored when I got the results! Has anyone have this happen to them?¿
 

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Do you have the numbers for O2 and CO2?

Generally, high HC can mean either rich or lean, high COs indicate a rich condition, and high NOx indicate a lean condition. Comparing these against the O2 and CO2 readings may make it easier to diagnose. Do you know what RPM range the engine was at when you failed?

I would start with the simple checks: O2 sensor, EGR valve, fuel pressure, etc.
 

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Discussion Starter #3
it says it was tested at 40km/h and said rpm was 1962 the result on that says valid. I have a repair manual it tells you how to check the o2 sensor, I did pick up a new o2 sensor, but I guess I'll check the current one before I go about replacing it.
 

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We just started emissions diagnosis in school, so maybe one of the charts from my book will help lead you in the right direction:

Causes for excessive HCs and COs:

Plugged PCV valve or hose
Fuel in the oil
EVAP canister is saturated
EVAP purge valve stuck open
Defective TPS

Excessive NOx:

Vacuum leaks
Head gasket failure
Carbon on the pistons
EGR stuck closed
Stuck fuel injectors
Low fuel pressure
Overheating
O2 Sensor failure


My other book said pretty much the same thing, except for under HC, CO, and NOx as separate symptoms, it pointed to the catalytic converter, which makes sense, since NOx and CO/HC levels are on opposite sides of the rich/lean emissions diagnosis charts, and the cat is supposed to take care of all three.
 

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Discussion Starter #5
What I just noticed, sorry I didn't notice it earlier. They tested it running at 40km/h failed the three things I mentioned, but they also tested it as "curb idle" and everything says pass or valid.
 

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If you passed at idle, but not at a cruise, I'd suspect the PCV sysem and EGR valve. Make sure to check the hose on the PCV valve. Mine was packed full of carbon when I bought my car.

Is your car OBD1 or OBD2?
 

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Discussion Starter #7
Sorry I don't know what you mean by OBD1 and OBD2. So if it passes one part but not the other, it's probably not the cat converter?
 

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OBD 2 started in 95 cali and 96 federal Sentras. I'm asking because this is a general GA16DE forum which covers 91-99. If its OBD 2 you can have a parts store or garage run an emissions readiness scan that can tell you the condition of the EGR, O2s, EVAP, and other emissions systems. Is its OBD1, you're on your own.

If it passed at idle, but not at 40 km/h, I'd rule out the cat, since it should be equally effective at any speed (provided the engine it warmed up). The piston engine is very inefficient at idle (which is why most hybrids shut the engine down at idle). The systems that come into effect at a cruise are the EGR and EVAP. From what I've read since my last post, I'm leaning toward a lean condition, which could be a number of things. I'll try to remember to ask my teacher about your problem on Monday and see if he has any input. As I've said before, the O2 and CO2 readings will be very helpful in determining your problem, since they act as indicators of the real problem. There is a chart in one of my books that shows the relationship between the 5 gasses and the AFR.

If you have OBD2, see if you can get a free emissions readiness scan. If you have OBD1, check the EGR system and the O2 sensor first. Do you have a multimeter? Since my '93 Sentra has a one wire O2 sensor, I'm assuming its a zerconia (voltage generating) type (if I'm wrong, someone please correct me), which sends a variable voltage to the ECM. This voltage ranges from 0V to 100mV DC. Back probe the connector closest to the O2 (stick a sewing needle into the back of the connector alongside the spade contact so you can get readings while to ECM does. Take the positive reading from here and run the negative lead to the negative terminal of the battery). Look at the voltages and make sure it doesn't go out of the specified ranges. Then set the meter to hertz and look for 2-5 Hz (again, please correct me if I'm wrong, I'll look in my books and confirm the range on Monday). If your O2 fails either test, it needs changed.

There are several things to check on the EGR valve. The easiest is to let the engine idle and to manually pull up on the diaphragm and see if the engine sputters or stalls. If nothing happens, the passages are clogged, if the valve doesn't move under hand pressure, its stuck.

Try these things and let me know what you get. I'm a tad drunk, so I may have left something out. Feel free to ask questions.
 

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Discussion Starter #9 (Edited)
Thank you very must for those tips! Yeah I read up in my repair manual about the EGR, that is definitely a good place to check. One of my bosses is very good with cars. He gets OLD trucks, gets them running and puts them to work like a 56 International trucks he's got. He's also got a 1925 half ton he fix up for the hell of it but anyway yes you are correct about the O2 sensor it is a single wire. I imagine my 91 sentra is pretty much the same car as your 93.
 

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Discussion Starter #10
Well yesterday I changed out the O2 sensor, but the a lot of times when I stop for a light or stop sign the engine sputters slightly, I don't know what that's about, but I think tomorrow I'm gonna check the EGR valve. I need to get this figured out.
 

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Discussion Starter #11
Well, Went to take it my car in for a retest at a different place this time and guess what, they said they couldn't test it, im like what? They said the cat converter is missing, yes missing. I was in shock. Some idiot put two resonators where the converter is supposed to be, just my luck. They directed me down the road to a local brake and muffler place. The guy took a look under the car and was like wow. He told me what they coulld do it cut the resonator out and place a cat converter in and it would be $200. Oh I was so happy I could hugged him. So now I am finally retesting the car tomorrow and hopefully that was the problem ha ha.
 

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Let me know if that was the fix. Like I said, I'm in school for this stuff. Any information will make me a better tech in the end.

My Cavalier had a straight pipe when I bought it, but I live in an e-check free county.
 

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Discussion Starter #13 (Edited)
Yeah it passed with flying colours!! I am wondering something, I noticed in the repair manual says to disconnect the negative battery terminal when changing the o2 sensor , which I didn't do. Ever since I switched out the the o2 sensor it has a big of a rough idle when in drive. Should I try disconnecting the battery and reconnecting it to reset the computer? Or should I just leave it? Cause I am getting better gas milage cause according to the liters of gas I've used I've got 380 km out of slightly less than half a tank with combined city and highway driving!
 

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They tell you to unhook the battery for almost anything underhood. Its just a precaution in case you break a wire or drop a wrench in the wrong place.
 

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Well yesterday I changed out the O2 sensor, but the a lot of times when I stop for a light or stop sign the engine sputters slightly, I don't know what that's about, but I think tomorrow I'm gonna check the EGR valve. I need to get this figured out.
My car sputters a little too when i come to a stop. My brother's honda accord does too. My '97 sentra gets 50 mpg on the interstate and about 42 around town, and no error codes, so i'm pretty sure it's not a problem. I've had it for a year and it's always done it.

it's likely the added load applied to the engine through the alternator because of power breaking. it does the same thing when you idle and turn your headlights on--just not to the same extent.
 

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Discussion Starter #16
I don't notice it happening anymore. My car has never experienced an Ontario winter so I hope rust the salt doesn't eat it alive cause it's in great shape.
 
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