I failed emissions!!! :(

[DanRC30]

Ok, I just got my car back from the dealer where they did the timing belt job. I was almost home and my check-engine light went on. I parked the car and called the dealer. They said bring it back and we'll take a look. Got back in the car and the light was off! Hhhmmm..... I went up there anyway to see what may have happened. They said it threw a code showing the front O2 sensor. But the light was off so I figured I was alright. I was fine until I went through the inspection station and I failed on emissions. Here are the results:

HC is 739 (supposed to be under 100)
CO% is 3.89 (supposed to be under 0.50)

So here's my question... would the front O2 sensor send these readings this high or could it be something else?

Any thoughts?

Thanks,
---Dan

 

[Daedalus]

It's running rich. Can't confirm if it'll cause those numbers specifically, but if something's wrong with the sensor the car will be in open loop mode and run rich. The car has a hard time figuring out if the O2's working, since it doesn't work when cold. So not having a check engine light on doesn't necessarily mean it's working. The code is stored when the light comes on, and you can always check the code yourself.

 

[DanRC30]

The dealer checked and said that it showed a code for the front O2 sensor. Check engine light is off... should I replace it anyway? Seems kinda odd that it's bad since it only has 52k on it now... but I guess condensation could get in there and rust it out... no?

 

[Daedalus]

What year is the car?

 

[DanRC30]

1991, 52k mi.

 

[OLDMNSX]

Since they just did the timing belt I would check that the front O2 sensor harness is securely attached at the lower/forward edge of the forward bank valve cover. You have to disconnect the harness there to remove the valve cover and it can kind of be a PITA to get reattached. This could throw a code since it isn't connected and that is why it is running SO rich. The two may be together but just not snapped in place. That's where my money is!
Brad

 

[Daedalus]

Wouldn't surprise me. Pin could be bent too. But the heater circuit, at least, is complete. Otherwise the check engine light would have come on from the start and stayed on. Inspect the pins and recconnect properly.

 

[DanRC30]

The car needs to go on the lift for that right?

 

[Daedalus]

Not at all. You only need to get to the harness connector, not the sensor itself. The connector is at the top of the engine. See page 11-32 in the service manual.

 

[DanRC30]

Thanks, I found it, but damn... I can't seem to get it disconnected!

 

[DanRC30]

Ok, I got it disconnected. No bent pins and I checked resistance between the two lower pins C and D and it reads 13.2ohms. I went to the next step and checked all pins to see if any were grounded, and nothing showed. I'm onto the next step but it seems to get a bit hairy here...

Ok, so I turned the power on and measured the volts across C and D, and it read 14v. Next it says to disconnect the A connector from the ECU. That's where I stop because I don't know what that is... lol!

 

[goldNSX]

I may be a little bit 'fast' with my conclusions but TB + failed emissions right afterwards could be a TB a tooth OFF. Not to throw an arrow in the wrong direction but I know of other cars where it happened. Of course, it can be anything else as we don't have more info than 'TB-job' without the particular steps done.

Better get your car back to the dealer as they're responsible for their work.

 

[Daedalus]

My apologies for not being clear. I mentioned 11-32 for the pictures showing where the connectors are. The procedures on that page are to test the heater, which wouldn't cause the emissions failure, and which wouldn't cause the check engine light behavior you're seeing. Sometimes just wiggling a harness connector will fix a bad connection.

GoldNSX is right; having such a major service done prior to the light is quite a coincidence. If indeed the timing belt is off a tooth it will show up in a vacuum test, which is fairly easy to do.

 

[DanRC30]

My apologies for not being clear. I mentioned 11-32 for the pictures showing where the connectors are. The procedures on that page are to test the heater, which wouldn't cause the emissions failure, and which wouldn't cause the check engine light behavior you're seeing. Sometimes just wiggling a harness connector will fix a bad connection.

GoldNSX is right; having such a major service done prior to the light is quite a coincidence. If indeed the timing belt is off a tooth it will show up in a vacuum test, which is fairly easy to do.

The only other info I can give is it had a good inspection sticker on it from 2 years ago, and it had no more than 10k miles on it since then.

How do I do this vacuum test?

 

[Daedalus]

Let's back up a little before we get too spun up.

1) Originally I just wanted you to make sure the connector was on good and then drive the car to see if that made a difference.

2) It's possible the check engine light was a quirk. Clear the code and do the test on 11-30 to see if the light comes back on.

3) When you did the emissions test are you certain the engine was fully warmed up? O2 sensors and cats only work when hot.

4) Do you have any reason to believe the belt is off a tooth? Does the car feel any different now than it did before the replacement? If you want to do a vacuum test you'll need to buy or borrow a vacuum gauge.

5) The simple answer--the sensor is just bad--is always possible.

 

[DanRC30]

Let's back up a little before we get too spun up.

1) Originally I just wanted you to make sure the connector was on good and then drive the car to see if that made a difference.

2) It's possible the check engine light was a quirk. Clear the code and do the test on 11-30 to see if the light comes back on.

3) When you did the emissions test are you certain the engine was fully warmed up? O2 sensors and cats only work when hot.

4) Do you have any reason to believe the belt is off a tooth? Does the car feel any different now than it did before the replacement? If you want to do a vacuum test you'll need to buy or borrow a vacuum gauge.

5) The simple answer--the sensor is just bad--is always possible.

The light went off after re-starting the car. But that was the only time I ever saw the light go on, and that was after the TB was done. It was fully warm as I drove it for about 45 min after taking it home from the dealer. I brought it back to them and that's when they told me it threw that front O2 sensor code. I assume they cleared it for me, but who knows...

Unfortunately, I can't notice much of a difference since I just bought it about 2 weeks ago and didn't drive it because I was waiting to get the TB job done to be safe. Looking back however, I think the car did feel a little more ballsy before the TB was done, but it's really hard to say for sure.

I am dropping it back off at the dealership tomorrow and they are going to look at it next week for me. The high emissions levels are hard to explain away other than the timing being off as far as I can see.... I mean, the levels are over 7x what they should be.

Just to be sure, I'll ask them to check the sensor to see if it's good... if they have a way of doing that.

 

[DanRC30]

Well, I dropped the car back off at the dealer on Saturday. I called today for status and they said they'd check the timing in the next day or so and that's all they can do. They think it's right and they tried to say that the car "runs rough". (That's a nice thing to hear from your dealer right?) Especially when it actually has sound because of the aftermarket headers, intake and exhaust on it. Then he said the exhaust mods could affect the emissions. Problem is the mods were done YEARS ago! Fact is, the car did not run rough. It passed inspection every year without issue and only has 52k on it now. Could the O2 sensor have gone bad? It's possible, but I did check it out on the ohm meter and it read 13.2 which is correct according to the book (unless I'm reading something wrong).

I'm pretty miffed about this whole thing... even if the O2 sensor was bad, I find it very hard to believe that the emissions would be THAT high. It's almost 8 times the max legal number. The timing simply has to be off. Anyone agree/disagree? I'd like to hear some comments on this if you all don't mind...

 

[Daedalus]

he said the exhaust mods could affect the emissions.

Not unless the catalytic converters were changed or have been damaged/degraded. The O2 sensor is still in place and the exhaust past the cat has nothing to do with emissions.

Could the O2 sensor have gone bad? It's possible, but I did check it out on the ohm meter and it read 13.2 which is correct according to the book (unless I'm reading something wrong).

Yes, sensor could be bad. Read the manual again. The test you did was for the heater, not the actual sensor. There are 2 circuits in the part. One that gives O2 readings, and one for the heater. The heater is only there to help get the O2 sensor working faster from a cold start; once the sensor is hot enough, the heater is not needed. If the heater were completely dead, it would just take longer for the sensor to give O2 readings, but there would be no effect on emissions as long as the sensor was hot and working. It's difficult to test the actual sensor is working on OBDI cars.

even if the O2 sensor was bad, I find it very hard to believe that the emissions would be THAT high. It's almost 8 times the max legal number. The timing simply has to be off. Anyone agree/disagree? I'd like to hear some comments on this if you all don't mind...

Not sure what to say. I honestly don't know how much of an effect a bad O2 sensor or a mis-timed belt would have. This kind of info isn't easy to come by.

 

[Daedalus]

What exhaust mods do you have? If you have a header, and if there's an extension wire on the O2 sensor, it's possible they may have mixed up the connections on the 2 sensors. It has happened before with header extensions. They would have had to disconnect both to do the timing belt.

 

[DanRC30]

Point taken Daedalus. But here's my thing... I've had O2 sensors go bad on other cars, and the emissions isn't even nearly as high as what this thing is. On my nissan the emissions were like .5 higher across the board... not almost 8 times! Sigh... I have a feeling this isn't going to turn out good...

 

[DanRC30]

What exhaust mods do you have? If you have a header, and if there's an extension wire on the O2 sensor, it's possible they may have mixed up the connections on the 2 sensors. It has happened before with header extensions. They would have had to disconnect both to do the timing belt.

Comptech intake
Comptech headers
HKS Exhaust

 

[MikeW]

...If you have a header, and if there's an extension wire on the O2 sensor, it's possible they may have mixed up the connections on the 2 sensors...

+1

You should follow the cables to verify that the O2 sensors are really connected to the right cylinder row.
The fuel control of each cylinder row is looped independently with an own O2 sensor.
If you mix them up = no correct fuel control = bad emissions.

If your engine is running on all cylinders, there is fuel, compression and spark...
So I would not be concerned too much about expensive parts and repairs. :smile:

 

[DanRC30]

Thanks Mike. I told the people at the dealer this and they're going to have their NSX guy look at it tomorrow.

I did some digging through the paperwork that came with the car and I found emission results from 01. It passed emissions every year as per the original owner, but this was the only record he saved. Here's what it said:

That's a far cry from what I got this time around which was:

______ Standard __________ Reading
HC: ____ 100 _______________ 739
CO: ____ .50 _______________ 3.89

 

[DanRC30]

Here's the latest:
The dealer said the timing is right on the car. They said they checked it out and it was done correctly. They suggest I replace the O2 sensor as a start. Well, I plan on changing the plugs and the O2 sensor and see what happens. I also plan on doing that vacuum test to make sure the timing is right. Larry went over how to do that briefly on the phone, but I'd appreciate it if someone could put it in writing so I can test it properly, I'd appreciate it.

In case this doesn't do it, can anyone think of anything else that would cause this uber-high emissions problem?

 

[PATCHEZ]

This may sound wrong and it is very rare and yes I have seen it. If the 02 is reading a neg signal cracked or grounded in some way it will read super lean and it looks like ur running really rich. So the O2 is reading lean and the computer keeps adding more fuel.Try scoping the 02 and see what type of signal its giving off.