Failed CA smog test (Help)
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From: usa
Failed CA smog test (Help)
Okay, i have a 94 civic CX, took it to smog yesterday and it failed....All stock...no check lights....smog guy says that it's probally running too lean.... can a all stock civic be running lean??? please help!!!
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From: Locash
Re: Failed CA smog test (b20vtech)
Of course it can run lean. The engine is full of maintenance parts. Assuming the motor is good, just catch up to the maintenance schedule (basically do a comprehensive tune up) and you should be fine.
Many people take the approach of just diagnosing the offending part/sensor, which is fine. But I look at smog checks as a way to force people to keep up with the regular maintenance. So I will R&R all the regular maintenance parts when the time comes.
That doesn't necessary mean replacing everything. Some things like plug wires just need to be looked over. But oil, plugs, rotor should definately be replaced. Cap should be checked out and brushed clean if it's good or just replace it. Check how long it's been since the fuel filter has been replaced. I always remove the throttle body and clean it out along with the IACV. I like to pull the IM and clean it out every couple years. Seafoam the motor. Check/adjust ignition timing. Make sure the car idles at spec RPM. Test O2 sensor for laziness using a voltmeter. Check for CELs. Check the fuel pressure. I send out the injectors to RC for cleaning at least once for every motor. Pull out the IAT and wipe it off. Pull out the coolant sensors and brush them off whenever you get around to changing the coolant. Also make sure the engine isn't running too hot/cold. The thermostat and radiator cap are easy to replace if they're the culprit. If the engien is operating out of operating temperature range then it most definately will affect the AFR.
Many people take the approach of just diagnosing the offending part/sensor, which is fine. But I look at smog checks as a way to force people to keep up with the regular maintenance. So I will R&R all the regular maintenance parts when the time comes.
That doesn't necessary mean replacing everything. Some things like plug wires just need to be looked over. But oil, plugs, rotor should definately be replaced. Cap should be checked out and brushed clean if it's good or just replace it. Check how long it's been since the fuel filter has been replaced. I always remove the throttle body and clean it out along with the IACV. I like to pull the IM and clean it out every couple years. Seafoam the motor. Check/adjust ignition timing. Make sure the car idles at spec RPM. Test O2 sensor for laziness using a voltmeter. Check for CELs. Check the fuel pressure. I send out the injectors to RC for cleaning at least once for every motor. Pull out the IAT and wipe it off. Pull out the coolant sensors and brush them off whenever you get around to changing the coolant. Also make sure the engine isn't running too hot/cold. The thermostat and radiator cap are easy to replace if they're the culprit. If the engien is operating out of operating temperature range then it most definately will affect the AFR.
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From: San Ramon/Pleasanton, CA, USA
Re: Failed CA smog test (b20vtech)
Lean is easy. vacuum leak, blocked injector, etc...
However if you haven't messed with anything and the car seems to be running good, then usually the O2 sensor.
Now you say if it was bad wouldn't the CEL come on. In some cases yes and in some no. My O2 sensor got stuck at .5 volts and no CEL.
Replaced it and I'm back to passing.
However if you haven't messed with anything and the car seems to be running good, then usually the O2 sensor.
Now you say if it was bad wouldn't the CEL come on. In some cases yes and in some no. My O2 sensor got stuck at .5 volts and no CEL.
Replaced it and I'm back to passing.
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Joined: Oct 2001
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From: SoCali, CA, USA
agree
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thesmogman »</TD></TR><TR><TD CLASS="quote">Now you say if it was bad wouldn't the CEL come on. In some cases yes and in some no. My O2 sensor got stuck at .5 volts and no CEL.
Replaced it and I'm back to passing.</TD></TR></TABLE>
I spent many hours trying to troubleshoot my z6 failing smog. My o2 sensor never swung back and forth. I tried swapping out every EFI component -- no change. 2 new o2 sensors. Didn't matter.
Turns out my modified engine harness was slightly incorrect. I replaced it with a virgin harness -- o2 sensor started working properly.
Check the o2 voltage .. and report back.
Replaced it and I'm back to passing.</TD></TR></TABLE>
I spent many hours trying to troubleshoot my z6 failing smog. My o2 sensor never swung back and forth. I tried swapping out every EFI component -- no change. 2 new o2 sensors. Didn't matter.
Turns out my modified engine harness was slightly incorrect. I replaced it with a virgin harness -- o2 sensor started working properly.
Check the o2 voltage .. and report back.
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Joined: Jul 2006
Posts: 2,817
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From: Kansas
Re: Failed CA smog test (thesmogman)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thesmogman »</TD></TR><TR><TD CLASS="quote">Lean is easy. vacuum leak, blocked injector, etc...
However if you haven't messed with anything and the car seems to be running good, then usually the O2 sensor.
Now you say if it was bad wouldn't the CEL come on. In some cases yes and in some no. My O2 sensor got stuck at .5 volts and no CEL.
Replaced it and I'm back to passing.</TD></TR></TABLE>
Lean is not always easy... crack in exhaust manifold prior to O2 sensor....
If you fail NOX you are running lean in some way, the only time that NOX forms is with high exhaust/chamber temps (1200-1600degrees) If your EGR is inoperative (eventually they clog with carbon) this will make you fail, EGR is there to reduce NOX by cooling exhaust in the intake and thus reducing combustion temps by way if introducing an inert gas.
A typical reading goes something like this:
HC 10-25ppm (ideally 0)
NOX 350ppm or less
O2 0.5% or less
CO2 12-20% ideal
CO 0.5% or less
HC indicates unburned fuel, as im sure you all know.
NOX indicates high combustion temperatures, which is combated with EGR
O2 is your lean indicator, if your NOX is high, odds are O2 will be above normal, making a lean condition the cause of high NOX.
CO2 is your combustion efficiency, when there is enough oxygen present for combustion, it forms the more stable CO2, indicating enough Oxygen available to combust the HC available.
CO is the rich indicator. If this is high, odds are HC is as well, because there is not enough O2 present to form CO2, so it forms CO instead.
Bring your test results in and ill be able to help pinpoint your problem. These people should be giving you a smog sheet, don't take it to a place that doesn't
If its a driveability issue it wouldn't come on, say the EGR passages clogged, but the pintle in the EGR valve still operates, no gas is flowing (or not enough) but the PCM doesn't have a sensor to ensure it gets in the manifold or not.
Is that the VTEC-E motor? The D15Z1 is a lean burn design, and by normal operation it runs lean, and has a huge EGR to stop all the NOX it makes....
However if you haven't messed with anything and the car seems to be running good, then usually the O2 sensor.
Now you say if it was bad wouldn't the CEL come on. In some cases yes and in some no. My O2 sensor got stuck at .5 volts and no CEL.
Replaced it and I'm back to passing.</TD></TR></TABLE>
Lean is not always easy... crack in exhaust manifold prior to O2 sensor....
If you fail NOX you are running lean in some way, the only time that NOX forms is with high exhaust/chamber temps (1200-1600degrees) If your EGR is inoperative (eventually they clog with carbon) this will make you fail, EGR is there to reduce NOX by cooling exhaust in the intake and thus reducing combustion temps by way if introducing an inert gas.
A typical reading goes something like this:
HC 10-25ppm (ideally 0)
NOX 350ppm or less
O2 0.5% or less
CO2 12-20% ideal
CO 0.5% or less
HC indicates unburned fuel, as im sure you all know.
NOX indicates high combustion temperatures, which is combated with EGR
O2 is your lean indicator, if your NOX is high, odds are O2 will be above normal, making a lean condition the cause of high NOX.
CO2 is your combustion efficiency, when there is enough oxygen present for combustion, it forms the more stable CO2, indicating enough Oxygen available to combust the HC available.
CO is the rich indicator. If this is high, odds are HC is as well, because there is not enough O2 present to form CO2, so it forms CO instead.
Bring your test results in and ill be able to help pinpoint your problem. These people should be giving you a smog sheet, don't take it to a place that doesn't
If its a driveability issue it wouldn't come on, say the EGR passages clogged, but the pintle in the EGR valve still operates, no gas is flowing (or not enough) but the PCM doesn't have a sensor to ensure it gets in the manifold or not.
Is that the VTEC-E motor? The D15Z1 is a lean burn design, and by normal operation it runs lean, and has a huge EGR to stop all the NOX it makes....
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