I believe the smog tech knows emissions and is correct - lean misfire.
High HC in a lean misfire makes perfect sense because either the air fuel mixture is too lean to burn or the A/F mixture is not getting an adequate spark, hence the fuel does not ignite and it exits the car as unburnt fuel.
It is interesting that it only shows up in the 25 mph test. Difficult to understand how such a small difference in rpm/speed could be the tipping point.
Air - Fuel - Spark. Troubleshoot until you find which is the root cause of the misfire. It could be the distributor, spark plug wires, fuel pressure regulator, alternator, vacuum leak, the list goes on and on. Good luck and I hope you pinpoint the cause quickly. I would be very sad indeed if I couldn't use my VX because of emissions. Just love that 50 mpg.
Based on my experience with my VXs I would suggest:
Looking at the top dead center/ crank shaft position/ cylinder position sensors. All of which reside in the distributor and can give bad information to the ECU if they are not working properly. In turn the ECU will respond with bad information back to the engine. I replaced my distributor with a NEW not rebuilt distributor because rebuilts are often very poor quallity. The new distributor actually costs about the same as a rebuilt anyway.
Checking the Map Sensor next. Honda's Trouble Shooting Guide lists the MAP sensor as a possible problem when the vehicle fails the emissions test. It can reveal itself as a lean misfire if the information to the ECU doesn't express the engine load correctly. This is even a more acceptable choice since you are not experiencing a problem from one load level to the next. I always replace mine initially.
The LAF sensor is also on the list but since your car passed the low speed I feel it is probably working correctly.
The EGR and its controls (D15Z1 only) are also listed and are a likely possibility since their operation is during the timeline you describe.
Fuel pressure and injectors can cause such problems but usually reveal themselves as a loss of power and/or rough running under cruise conditions. How does your VX run under acceleration?
Under evaporative emissions control you might look at the evap purge control solenoid on the back of the intake manifold for a vacuum leak at the speeds where you experience the problem. (Unlikely)
Yes, my VXs go into lean burn in first gear and as I recall 10 mph is the low VSS requirement.
Don't mess with the LAF sensor. The parameters that are engineered into both the LAF sensor and the ECU depend upon each other. There is a preset voltage range supplied to a 5 wire: 2 sensor wires, a sensor ground, and a regulated resistor for the heater input. Since five wire LAF sensors have two zirconium elements as opposed to the four wire's one, it's not possible to run your ECU with a four wire.
Thanks for all the info guys. I rebuilt my distributor today at work. I changed the cap, rotor, coil, distributor seal and o-ring. Oh by the way the spark plugs were replace less than 5k ago and i tested the them and they are good. I dont want to replace anything that is not bad, because i want to see if i can pin point the root of the problem. I also checked the fuel pressure and its within spec. I will set the timing tomorrow. And by the way we tried messing with the timing during the test and it did not effect and emissions readings.
Another thing that i just remembered was that when i first bought the car the car just passed smog. But then again i bought it from a guy that ran a smog station. So i cant be sure that i actually passed the smog test. But the car had two cats on it. It had a factory replacement catalytic converter and a converter welded under the car. I originally thought the front cat was plugged, but when i took it apart to fix an exhaust leak. It look fine and looks to have been recently replaced. So i removed the second cat under the car. It was killing the power a little.
After i check a few things, i will try to smog my car with it in 16v mode. I assume that once its in 16v mode, it will not engage lean burn.
I went to the smog station retested my car after the repairs that i listed above. The results were the same. I passed the 15mph and failed the 25mph, HC in the 300 range. While the car was in the 25mph test, i manually put the car in 16V. And the HC dropped to 70, which is in the pass range. The CO and NOx went up, but still within the pass range. But I now fail the 15mph test. HC(75), CO(.6) and failed the NOx 1000.
When i put the car in the 16V mode, the cel came on. The limp mode is cutting off the egr and causing the engine to run a little rich.
My next smog test will be with the vtec solenoid energized along with the oil pressure switch on the solenoid bypassed. Then the car will be in the 16v without the cel. I will also clean the egr passage. I dont want to smog it again.
How does your car drive? Mine has the exact same problem (federal car, failed smog due to high HC @ 25mph, co and nox very low).
I ask because I think this may be related to the smog, but my car doesn't have smooth/consistent power delivery. When it's cold it runs fine, but when it warms up it randomly bogs/misses/hesitates/stumbles on acceleration and also under constant load and rpm. It will alternate between this and running fine.
I put in new spark plugs and wires and it still does this. I just bought a new (5 wire) O2 sensor, so I'm gonna try replacing that this weekend. I'll let you know if that makes a difference.
It feels like it's constantly kicking in and out of lean burn. Sudden loss of power, then surges, then loses power again. Does your car do this too?
I gapped the plugs to the factory spec and i have a brand new factory coil.
Mad Pup- I can stay in lean burn if i am easy and steady with the gas pedal. I does not just fall in and out of lean burn by it self. My car accelerates smoothly, it does not miss and surge. My car use to run like your car, i replaced the O2 sensor and it fixed the problem. But my car had a code for the O2 sensor so that made it simple.