QuestionQUESTION: Hi, my engine pinged under heavy load and this diminished with high octane gas. I took it in for service and the flame trap was not put on correctly previously, and it leaked oil. With the new flame trap put on, the pinging stopped and the car seems to have more power up hills. Why?
ANSWER: Kevin,
The only thing that I can think of is that the flame trap caused a vacuum leak and made the fuel mixture too lean.
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QUESTION: At the time of the bad flame trap arrangement, the car almost failed smog. It never had this problem before. The problem was NO--everything esle was fine. What would cause high NO but low emissions for everything else? Bad flame trap?
AnswerKevin,
An inoperative EGR system. The EGR system was designed specifically to reduce NOx; that's it's only function. The EGR, which stands for Exhaust Gas Recirculation, allows exhaust gas to enter the combustion chamber through the intake. The exhaust gas has a cooling effect on the combustion chamber.
Over advanced ignition timing. The more advanced the ignition timing, the higher the combustion chamber temperatures.
Overheating. If the engine temperature is too high the NOx emissions will go up.
Lean air/fuel mixture. If the air/fuel mixture is too lean the combustion temperature will go up.
Compression over specification. Normally when we think of engines aging we think of the compression going down. However, there are a couple of ways the compression can increase as the engine is used. One is carbon buildup on the tops of the pistons. When carbon forms on the tops of the pistons, the combustion chamber area decreases and the compression ratio increases. The carbon can be manually scraped off the tops of the piston to correct this problem, but that would require disassembling the engine.
Mysterious reasons. Sometimes NOx is too high and there's no obvious cause: the EGR works, the timing and advance work normally, the engine temperature is within range, the air fuel mixture is good, and the compression is within spec.. When this happens you can try a little tweaking. If there are two thermostats listed for the car, use the cooler one. If there are two spark plugs listed for the car, use the cooler one. Retard the timing 2 degrees (the maximum allowed). Clear out the EGR passage even if the passage seems fine. Cross your fingers.
