Due to the age of the FC's, the stock wiring system is susceptible to voltage drops due to corrosion and loose connections.  It is not surprising to measure voltage to the fuel pump at 10-11VDC!  Fuel pumps are very dependent on voltage input; the lower the voltage input the lower the fuel flow.  Ideally, the fuel pump power wire should the same voltage as measured at the battery terminals.

On FC3S turbos, the fuel pump sees two levels of voltage depending if the engine is in boost - the "low" voltage level runs the fuel pump circuit through a resistor to drop the voltage to 9-10VDC; the "high" voltage level run full, unmolested voltage to the fuel pump.  The fuel pump also sees full voltage when cranking the starter.  You need to have the turbo under boost to check to see if your fuel pump is getting full voltage.

As much as this emphasis is on the fuel pump, sometimes it's not the fault of the wiring; the early 1986-1988 FC's run a very overrated alternator charging system.  Although officially rated at 70 amperes, most units only put out 60-65 amperes maximum in top condition.  Add age and wear-and-tear into the whole equation, and you get charge currents dropping into the 50A range!  As current capacity drops, voltages drop.  Decreased fuel flow from the fuel pump is not far behind!  Decreased fuel flow leads to possible lean conditions for the engine - this means death to the motor under heavy boost.  A significant number of FC's have blown their engines at night, where the increased current load of headlights, stereos, and A/C systems stress the alternator enough to drop voltages!

Bottom line, make sure your battery and alternator are in good, working condition.  Also make sure your fuel pump gets full voltage under boost.

Using a voltage meter (digital multimeter or DMM), check the voltage at the battery terminals.  With the engine not running and all electrical systems off (i.e. headlights off, AC off, no brakes, doors closed), a healthy battery should be showing at least 12.5VDC.  Borderline would be anything over 12.0VDC.  A battery showing under 12.0VDC would be considered on it's way out.

To check the alternator condition, start the engine.  Test voltage at the battery terminals again.  With all electrical systems off, the voltage should read above 13.5VDC at idle or at least 1.0VDC higher than the voltage level with the engine off.



Questions?  Comments?  Send mail to:  reted@fc3spro.com

10/04/2003