Ford Repair: 1995 ford f150 4.9 L manual trans., high octane fuel, combustion temperature

Question
Just failed an e test on high N.O.. the meachanic said is is usaully the egr valve. do you have any other sugg. on poss. causes? it has 360,000 kms. can i clean my egr valve on this model? and if so, any hints? thanks

Answer
It will be much more helpful if you pull the trouble codes. It could be the solenoid, or several other factors. Depending how close you were to passing, you can try these ideas.  Start with high grade gasoline. NOx gases are actually caused from engine combustion temperature being too high. High octane fuel can reduce the temperature. The EGR valve injects exhaust gas that actually cools down the combustion temperature. Also, look over your vacuum lines with a fine tooth comb. Even the slightest leaks can jack up the temps with a lean burn. Last but not least, if you are left with no alternative. Drive as close to the testing sight as possible. Park the truck for a minimum of 90 minutes to 2 hours. This should give the truck plenty enough time to cool off, then run through.