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