A gentleman takes a certain amount of pride in his motor. It goes without saying that the said motor, like the gentleman himself, should be in perfect working order. Imagine therefore my horror, when my jeep failed the test. Thus began a saga that cost me in excess of 50,000 rupees, a great deal of time and enormous heartburn. Here are some tips for the unwary. The information below applies to diesel vehicles.
The test being performed here is known as the is the Society of Automotive Engineers (SAE) J1667 Snap Acceleration Test. The link has more details but the basic test is to sharply accelerate to 'maximum operating revs'. The maximum is not precisely defined but is around 3000-3500 for diesels.
The test is conducted without load, so A/c, lights and all accessories should be off.
The test measures the opacity of the smoke, which is indicated by the k factor. The higher the k factor the greater the opacity of the smoke and thus pollutants.
The test is conducted (for diesels) by:
1. Inserting one probe through the dipstick (to measure oil temperature)
2. Placing a probe on the engine that derives the RPM from the engine vibration. This is a derived reading so it is important that this is placed properly so that the reading corresponds to the RPM counter in the vehicle. If you don't have an RPM counter read the manual or search the web to find out the normal idle speed on your engine. Usually engines idle at around 750-800 for diesel engines and slightly lower for petrol engines.
3. A third probe is placed in the exhaust. This is a light probe that measures the opacity (k factor). A beam of light is passed between two points on the probe and the strength of the light beam measured to identify the k factor. If you have fancy curved or twisted exhaust pipe it could cause problems. If you are in doubt, I found the full SAE J1667 test procedure (about 43 pages) on the web. This details the proper placement of the probe for unusual shaped exhausts.
The standard (or pass mark)
This is the standard according to the Government Gazette. However the dates are wrong. Since this is the first year of testing, the applicable k factor for diesels is 8.
The pass mark of 8 is pretty low: your vehicle has to be a real belcher to miss this target. The problem is that the test is performed thrice and the variance in the k factors between tests should not exceed 1.
To my mind high variance between tests should indicate an invalid test, but the system simply fails the vehicle, which is why it is important to ensure that the test is conducted properly.
If your vehicle fails the test examine the report carefully. Look for the average k factor. If it is below 8, then there will be the word "Pass" in small letters next to the average, although the overall result is "Fail". If this is the case, then your engine is generally ok, what you probably need to do is follow the test tips carefully.
Tips for success
The 4x4 Club has published some useful tips here. It is important to note that :
1. Engine should be warm, give it a good run before the test.
2. Stamp on the accelerator at least thrice, taking the RPM upto 3000-3500 and holding for a few seconds. This clears a lot of old soot and other pollutants trapped in the system.
3. Ensure that the probe monitoring the rpm is giving the correct reading. Once the probes are placed they should not be shifted around in between the the three tests. This could cause unusual variances between the tests thus resulting in a fail.
3. Make sure that all a/c, lights and all accessories are off.
If your vehicle does fail, try a new air filter or a change of fuel (to super diesel), these may cure marginal failures.
I did not realise any of the above when I took the jeep in for the test. It was failed with an average k factor of 1.17. It was failed on the variance. Had I known that the standard was 8 I would not have gone to too much trouble. Instead I foolishly listened to the staff.
I was asked to clean the air filter and to pressure the injectors and I foolishly went to to the garage and asked them to do this plus service the injector pump, all of which were entirely unnecessary. A good warm up and a few stamps on the accelerator to clear accumulated soot would have done fine.
Two overhauls of the injector pump, two rounds of pressuring the injectors, a change of the three main belts, replacing the main pulley (which got messed up probably attending to the other repairs) not to mention 50k poorer, I advise you guys its no big deal to pass, just make sure the test is conducted properly.