EMISSIONS. PLEASE HELP!

[dp94]

I'll make it short and sweet, I know everyone's tired of hearing about emissions failures.

- poured a bottle of guaranteed to pass in (followed instructions)
- took it for a spirited drive (to warm up the cats, and O2 sesnors), oil change. Plugs are new. Air filter is new. Fuel filter is new.
- Passed each portion of the test except for my HC at idle (<1250 RPM). The limit is 200HC, I was at an outstanding 1165HC.

- I ran the ECU for codes. I have the green light, CODE 55. next, I ran an O2 sensor diagnostic on it. My drivers side O2 sensor is slow (it does not blink rapidly, switching rich to lean).

Can anyone shed light?

[DCaff300ZX]

It's the O2 sensor, I had the same issue for with my NA and replacing them both (do both while in there) made for passing with flying colors. I had the exact same fail area BTW.

[dp94]

Thank you. I'm ordering my O2's now!

Also, out of curiosity, would a vacuum leak cause a lean or rich condition? I've been reading some inconsistent things.

I think it would cause it to be more lean but I could be wrong.

[NolimitZ32]

A vacuum leak would cause a rich condition if all your sensors are operating properly.

[dp94]

So then how is the emission test trick proposed to work?

[NolimitZ32]

What trick is that? Do you mean removing the vacuum from the fuel regulator?

[hannman]

I disagree with NoLimitZ32.

Under BOOST a vacuum leak would cause your car to run rich. If the manifold is under negative pressure, which it would be for an idle and 2,500 rpm test, that would make your car run LEAN, as the vacuum leak will suck in unmetered air.

Now if the vacuum leak is between the compressor and the air filter, this will cause a lean condition at all times, as the car will be sucking in unmetered air 100% of the time. Prior to the compressor is always under negative pressure.


As for your failing grade on the E-Test, I find it odd that you pass on CO and fail miserably with HC. High Hydrocarbon numbers are associated with poor / incomplete combustion. This often goes hand in hand with high CO which leaves me scratching my head. My first guess was plugs, but you have that covered. The O2's are likely the culprit. If that doesn't work I'd be looking at your coil pack connections to see if you have a poor electrical connection that might not be working well under a no-load situation.


ALL that aside … if you want to pass without going through the list of repairs, try an 80/20 mix of pump gas and methanol. I just ran this and went from failing on idle to barely getting over the level of detection on the analyzers. Grab a jug of Methyl Hydrate (methanol) from the paint section of your local hardware store. Put it in a gerry can and add 15 litres of low octane fuel. Mix well and then add to your near empty gas tank before heading to the test facility. Fill up with a no ethanol fuel (SHELL 91 if you're in Canada) AFTER you pass the test and worry about the laundry list of repairs for a weekend when you have spare time.

I'm a combustion specialist with the Ministry of the Environment - Not the office that manages the Drive Clean Program

[DCaff300ZX]

Interesting fuel concoction there hannman, I'll have to note that for future reference...thanks

[NolimitZ32]

I should have made a caveat in my post, yes 100% under boost a vacuum leak will cause a lean condition. I was assuming conditions under which the tests are performed.

[dp94]

Thanks for the insight hannman. How bad is this mixture for my car? I've placed an order for new O2's. They'll arrive next week Wednesday. Do you think I should install O2's plus fuel mixture and test? Or install O2's and test? Or fuel mixture and test?

Thanks again!

I disagree with NoLimitZ32.

Under BOOST a vacuum leak would cause your car to run rich. If the manifold is under negative pressure, which it would be for an idle and 2,500 rpm test, that would make your car run LEAN, as the vacuum leak will suck in unmetered air.

Now if the vacuum leak is between the compressor and the air filter, this will cause a lean condition at all times, as the car will be sucking in unmetered air 100% of the time. Prior to the compressor is always under negative pressure.


As for your failing grade on the E-Test, I find it odd that you pass on CO and fail miserably with HC. High Hydrocarbon numbers are associated with poor / incomplete combustion. This often goes hand in hand with high CO which leaves me scratching my head. My first guess was plugs, but you have that covered. The O2's are likely the culprit. If that doesn't work I'd be looking at your coil pack connections to see if you have a poor electrical connection that might not be working well under a no-load situation.


ALL that aside … if you want to pass without going through the list of repairs, try an 80/20 mix of pump gas and methanol. I just ran this and went from failing on idle to barely getting over the level of detection on the analyzers. Grab a jug of Methyl Hydrate (methanol) from the paint section of your local hardware store. Put it in a gerry can and add 15 litres of low octane fuel. Mix well and then add to your near empty gas tank before heading to the test facility. Fill up with a no ethanol fuel (SHELL 91 if you're in Canada) AFTER you pass the test and worry about the laundry list of repairs for a weekend when you have spare time.

I'm a combustion specialist with the Ministry of the Environment - Not the office that manages the Drive Clean Program

[hannman]

Obviously it's best if we all have our cars running as clean as possible. If your O2's are shot and dumping fuel as a result of a lazy signal, the best case scenario for you is to fix the problem, get your car running tip-top and move on.

If it were my car I would suggest swapping the O2 and testing to see where I land. I have no idea where you live, what the cost is for a re-test or even what Mod's you have on your car. If you have a boat load of other mod's (EGR delete, BIG Cam, Big injectors, stand alone with custom tune etc) you're probably gonna have a hard time passing the proper way. If you're close to stock, with an exhaust, an intake, nismo injectors, 2860 or 2871 turbos and an off the shelf tune from JWT, ASH or Z1, you should be able to pass a smog test without too much hassle.

If you test after replacing your O2's and pass, you have piece of mind that all is well and you don't have to worry for the next round.

If this car is your DD and your registration is expired and you NEED to get this done, I'd say throw everything but the kitchen sink a this thing and get it over with.

All alcohol based fuels are corrosive. They absorb water quickly and will eat away at rubber seals. An 80/20 mix of methanol or ethanol isn't going to kill your car though. In Ontario I think the gas stations have up to 15% ethanol in the fuel that comes out of the pump. Methyl Hydrate or methanol is used as a fuel stabilizer. It's used in various mixtures in race cars, drag cars, dirt bikes, airplanes… It's been used for decades. Do some research.

It WILL help you pass your SMOG test but you SHOULD NOT allow your Z to sit for any extended period of time with a high concentration of methanol in the tank.

Report back so we know how things went.