Nissan Repair: ignition timing, flowmaster muffler, drive pulleys

Question
I have a 2001 Frontier 2WD 4cyl 5speed manual 130,000 miles, thanks to you I narrowed a problem down to a bad catalytic converter and fixed the problem. My problem now is I always had engine ping especially with the a/c on, tried different gas and grades, same results. I retarded the timing a hair and solved the problem with no loss of power that I can tell but lost 4 mpg , mind you I do all highway driving 110 miles per day. I thought advancing the timing would give you less mpg? which way is it? Thanks Rich

Answer
Rich,

Advancing the timing gets you better mileage as long as the engine does not ping.  If you have pinging it will eventually beat the rod bearings out of the engine.  What happens is the fuel pre-ignites as the crank turns and when this happens that particular cylinder is trying to go against the way the rest of the engine is turning and this beats the upper rod bearing insert until it bends and the tab allows the rod bearing to spin.  I would not have it pinging.  But, you could go a degree or two more advance until the engine pings and then back it off until it does not and that is good as it gets.  You could do other things to get better mileage like a flowmaster muffler and a K&N air filter.  Also, there are under drive pulleys that get you better mileage.  Also, make sure that the tires are inflated properly.  You can go to the max on the tire but the ride will be harsh.  I always pump the tires up to more than the cars sticker.  Just be sure not to exceed the pressure on the tire itself.