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Discussion Starter · #1 · (Edited)
What is an Emissions Test All About?

Jersey failed miserably today. No charge (thank goodness).

HC over 2 times too high
CO about 5 times too high
NOx passed easily

What's it all mean? What changes these numbers if I want to do better? Read on my friend...
 

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Discussion Starter · #3 ·
Carbon Monoxide:

Measured in percent, this is the result of incomplete combustion. In other words, the fuel mixture has been compressed and ignited, but could not complete the combustion process due to the lack of oxygen. This failure is always mixture or ignition timing related. The ideal reading for CO is 0%. A normal reading for CO is usually around .25 to .75% with 1.2% being the failure mark in most areas for vehicles 1984 and newer. Earlier cars are allowed higher readings. Any car equipped with an Oxygen sensor will try to run under 1.0% as measured before the Catalytic converter (use that test connection for set-up). A vehicle with a CAT, O2 sensor, and an AIR system (Air Injection Reaction) will read almost 0% with everything working properly.

Most '70s cars should run between 1.0 to 2.0% with 2.5% being the usual failure point. I find that 1600 dual port will run fine in this range and with Fuel Injection, should be able to run about .5 to 1.5 %. Remember this is at idle so it is not an issue with overheating the heads and burning valves. '50s and '60s cars will need to run richer still to remain smooth running. Anything over 3.5 to 4.0% in any car is cause for concern although most test programs allow up to 6.0% for early vehicles. This is a lot of forgiveness in an inspection program. Over advanced ignition timing will also cause high CO readings at idle due to the idle speed control being set low in order for the engine to idle at a reasonable speed. VWs are especially sensitive to this. Keep this in mind when using different distributors.
 

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Discussion Starter · #4 ·
Hydrocarbons:

Measured in PPM (parts per million), this is the result of unburned fuel making it out the tailpipe. This is different from the CO problem in that here the fuel has not started combustion at all. This failure is usually caused by an ignition (misfire), or an engine problem such as a bad valve. An engine running too lean will often have excessive HC due to what is called a "lean misfire". Any leaks in the intake system or bad injectors will also cause excessive HC due to uneven fuel distribution.

Vanagons are very susceptible to the "lean misfire". Here the ideal reading again is 0 PPM. Most late model cars should run under 100 PPM with readings between 10 an 50 PPM being typical and a reading of over 220 PPM being the failure point for must inspection programs. Again, older cars are allowed more freedom although I find that most any car should be able to run under 400 PPM. My 1923 Haynes runs at 300 to 350 ppm HC and 4.0% CO. High HC readings are a little more challenging to trouble shoot because there are so many possible causes including a mixture or worse, a cylinder balance problem.
 

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Discussion Starter · #5 ·
Carbon Dioxide:

Carbon Dioxide is the end product of all Fossil Fuel combustion. CO-2, measured in percent is an indication of an engine's combustion efficiency. The ideal is 14% with most VWs running in the 12.5% to 13.5 range. CO-2 output is affected by timing (valve and ignition), compression, mixture, engine condition and temperature. The IM-240 tests will also measure the actual volume of CO-2 produced and limits will be set according to vehicle design. If centralized testing is coming to your area, be very careful of any modifications made to your vehicle. Even changes to your tires sizes and gear ratios will affect this test.
 

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Discussion Starter · #6 ·
Oxygen:

Measured in percent, is actually excess oxygen left over from the combustion process. If this reading is very low, then you will also experience high CO. In boilers and other equipment, we avoid high readings as that indicates excess air which reduces heating efficiency. In automobiles, we usually are looking for about 18%. Normal atmosphere is 21%. This is controlled in late model vehicles by the Oxygen Sensor circuit. The O2 sensor actually measures the Difference in O2 content of the atmosphere and the exhaust. When the atmosphere has more O2 than the exhaust, a small positive voltage is generated.

The Vehicle Computer (ECM), senses this signal and then adjusts the mixture accordingly. You can measure the fuel mixture of an O2 sensor equipped vehicle with a Digital Multimeter (DMM). If the mixture control system is working properly, you should see the signal fluctuate from .1 to .7 volts. This voltage correlates closely (not by design, just luck) with the actual CO percent (Example: .5 volt is approximately .5% CO). This is great news as we could install a universal O2 sensor in any car and use a DMM to set the mixture. If you wish to do this, ensure that you mount the sensor in a "hot " area of the exhaust as it has to be heated to 600 degrees F in order to function. This is why many cars included 86 and later Vanagons use a three wire sensor. The three wire sensor actual has a heating element built in to preheat the sensor. This enables the sensor to go on-line on a cold engine much sooner and keeps weather and driving conditions from effecting the sensor. I find that earlier Vanagons often have problems with sensor performance as the sensor is mounted far enough down stream in the exhaust that they don't get adequately heated during cold weather or when the engine is idling. This also creates havoc with emissions tests as vehicles are often tested without being thoroughly warmed up (car must be driven to properly warm up all emission equipment, especially the Cat).
 

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Discussion Starter · #7 ·
Failed the CO!

Check the Mixture and Ignition Timing. Especially on VWs, over advance timing will cause high CO readings. When setting up ignition timing, mixture, and idle speed, follow the book. On Digijet Vanagons, disconnect and bypass the Idle Stabilizer when setting the timing and idle speed. Resist the temptation to "advance" the timing for performance. Also make sure both the vacuum and mechanical advance mechanisms are working properly. On Digifant Vans, Disconnect the Temperature Sensor before setting the timing. Again, resist the urge to over advance the timing. Check the O2 sensor system to ensure it is working properly. Resist the urge to adjust the Airflow box. If the O2 sensor system is working properly, it will compensate unless some one has already made a mess of things. Also check the oil, diluted oil will also cause high CO readings. Worn rings and valve guides will contribute to this also. However this will only be a problem on very tired engines. Setting the idle speed around 1000 rpm will also help keep the CO readings down.
 

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Discussion Starter · #8 ·
Failed the HC!

Check the ignition system first. This usually caused by an ignition miss. Then check the engine. Poorly seated valves, leaking head gaskets, or other compression problems will put the HC readings through the roof. Also check for vacuum leaks and the injector spray patterns. Remember, HC failures are usually caused by compression or ignition problems. Improper fuel distribution/vacuum leaks will cause misfires that will cause excessive HC.
 

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Discussion Starter · #9 ·
Failed both CO and HC!

If the HC is very high and the CO is close, you probably have an ignition/compression related problem. If the CO is very high and the HC is close, than you may only have a timing/mixture problem. Use the above procedures accordingly and you should be able to resolve your emissions failure blues.
 

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Post Padder 2finger
 

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Discussion Starter · #14 ·
Compression Test

After removing all the spark plugs and spinning up the engine to get some cylinder oiling, all cylinders show 155 to 160 psi. I don't recall ever seeing compression that high, even on a fresh-built engine. I had to go back and re-do the first 3 cylinders as their readings were down in the 130 psi range.

Oiling made a 30 psi difference. Normal? Or do I have worn out rings that need oil to seal properly?

The spark plugs look absolutely horrible. I'm amazed it ran at all. At least one plug was so carboned up I couldn't see a gap. And the plug wires look like OE 1993. I don't see how this thing "just passed New Jersey inspection" without a little undocumented cash changing hands. The inspection is 6 months old according to the windshield sticker.

Anyhoo, I believe I have identified a major source of my emission ills.

So how exactly do you get the best results from RXP? Do you add it then go straight to inspection, or run a treated tank of gas through the engine, then go for inspection? If it's the latter, that's gonna be a bit tricky in a rig that ain't legal to drive on the street yet :)
 
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