Recent tune up, bad gas mileage?

[TommyyJ]

hey all

i recently did a complete tune up of the car, plugs, wires, cap, rotor, oil change, transmission fluid change, coolant change, you name it...but now it seems my gase mileage went down a bit...im thinkin it could be the plugs...they were pre gapped at .044...ive searched and found that your supposed to gap them between .039 and .043..is this accurate..? anything else it could be...i didnt replace my pcv, its a pain....but i doubt thats the problem...another thing, when i inspected my plugs it did show, well according to the spark plug chart, that i may be runnin hot or lean, the tips were a whitish color....thanks for any help

[Rev_D21]

Lean would increase gas mileage actually.

Perhaps the gap is too wide and you are not getting as strong a spark as your engine needs as a result. That would be wasting gas as you wold have an increase of blow by and weaker overall output. Have you checked your fuel filter. The three things you should check in this order are:

1)Air2)Fuel3)Spark

You problem will lie in one of those 3 there. So hone your diagnostic skills and start narrowing down systems till you have isolated the problem. Fixing it will be cake from there. Do some basic tests to start and work your way up from there.

[autotech43]

The larger the gap, the more spark is exposed to the air/fuel mixture. A larger spark plug gap increases the efficiency of the burn in the combustion chamber. If your ignition coil doesn't provide enough voltage, increasing the gap on your spark plugs will result in fouling and misfiring. I remember in the early eighties we use to change the plugs at the 15,000 and 30,000-mile interval and have a customers concern of decreased fuel mileage since the plug change. The result is when the gap is slightly wider, which on a slightly worn plug the gap will be wider, you will have an increase in the spark and gas mileage will increase but only on an average of one to three MPG. But with today’s fuel prices, a lot of our Infiniti customers are looking at the concern of the miles per gallon, and on the other side of that, we have customers that could care less about the mileage, they want performance.I would suggest keeping that gap within the specifications, and if I remember correctly, it is .038 to .042, depending on the vehicle.As far as the tips being whitish in color, you could have many things that come into play causing a slight lean condition, I would first make sure you have the correct plug heat range, and go from there.A small vacuum leak, restricted fuel spray from the injectors, ignition timing. A good scan on the engine with consult or other generic scan tool can monitor the sensors and give you an idea in those areas.