Buy 2 cans of Berryman's fuel injector cleaner. Use one with
a full tank and then another with the next tank. You can
also try Redline.. but don't mix the two brands.
Most of the time when you have problems at 1/4 tank it's
the fuel pump. You might want to also replace the Fuel
filter. Get the Motorcraft plugs because the Bush plugs
have been known to cause problems..
