When Spark Plugs Improve your Horsepower and Fuel Economy

by : Brandon Wirtz

I bought a 97 Jeep Wrangler.  4.0 Liter inline 6, a gas guzzler for its size.  This one was eating even more gas than I thought it should 14 miles to the gallon Highway.  So I looked for low hanging fruit.  The Idle didn't sound quite right, so I assumed the spark plugs, or distributor was the problem.  $36 in spark plugs is a cheap fix, and never a bad investment, so armed with My Bosch Platinum 4's I swapped the plugs and wires.  Low and Behold Cylinder 1's plug was so fouled there wasn't a gap any more.  This means an instant increase in power of 1/6 or 17%.  I also dropped $24 on wires since they are easy to change, and disconnecting the old ones occasionally damages them.

Then for $25 I picked up an Oil Cloth Air Filter.  There are several brands, K&N is one of the more famous, my lesser known brand should perform as well, and cost half as much, so I'm happy.

A quick highway test over 40 miles resulted in going from 14 miles per gallon (mpg) to 20.  Not an amazing number by itself, but that is more than a 50% increase in fuel economy, and likely about the same increase in horsepower in torque. 

The time it took to go from 5 to 35 miles per hour in third gear went from 11 seconds to 5.  (This is a good way to sanity check power increases because even if your reflexes are a fraction of a second off even small power increases will move the numbers by hundreds of milliseconds, rather than tens of milliseconds that a 0-60 might do, so you are less dependant on the stopwatch)

I have ordered an Electric Fan to replace the belt driven one on the engine.  This is supposed to increase power and fuel economy by 10 HP, and 5 mpg.  I'm shooting for 5 hp, and 3 MPG.  Which would get me to 23 mpg, which is not the 30+ that my Mini gets, but would be a 60% increase from when I bought the Jeep.

I'll try to get one of the girls to do a video of how to do all of this.

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