F 150 4WD Pickup V8-302 5.0L (1986)
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Fuel Pressure
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Poor Power Ground
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Engine Not At Normal Operating Temperature
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HEGO Sensor
2.
Spark timing that is retarded from specification may increase exhaust gas temperature and shorten catalyst life. Refer to the following
procedure for service details.
a.
Check spark timing. Check base timing with spout disconnected. Set base timing to the specification on the vehicle emission decal.
b.
Check computed timing with spout connected.
NOTE:
COMPUTED TIMING IS EQUAL TO BASE TIMING PLUS 20~ BTDC +/- 3~.
3.
Misfiring spark plugs may cause an unburned fuel air mixture to pass through the catalyst, which could cause higher than normal catalyst
temperatures. Refer to the following procedure for service details.
a.
Check secondary ignition, hook the vehicle up to an engine analyzer and check for a secondary ignition misfire.
NOTE:
SERVICE ANY ITEM THAT IS NOT PERFORMING AT PROPER SPECIFICATIONS BEFORE CONTINUING.
4.
Fuel pressure that is too high may cause rich air fuel mixtures to pass through the catalyst which could cause higher than normal catalyst
temperatures. Refer to the following procedure for service details.
a.
Check fuel pressure, install fuel pressure gauge, start and run the engine at idle. Fuel pressures between 28 and 34 PSI are typical (4.9L
typically is 15 PSI higher).
b.
Disconnect the vacuum line going to the fuel pressure regulator. Fuel pressure typically jumps to 40 PSI +/- 3 PSI (4.9L typically is 15
PSI higher). Visually inspect vacuum line for raw fuel.
NOTE:
FUEL PRESSURES ABOVE THESE VALUES SHOULD BE CORRECTED. HOWEVER, THIS MAY NOT BE THE CAUSE OF
THE CONCERN. SERVICE AS NECESSARY.
5.
Throttle plates in the throttle body not returning to the proper closed position may cause excessive catalyst temperatures during downhill
grades. Refer to the following procedure for service details.
a.
Visually inspect the throttle body and linkage for:
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Binding or sticking throttle linkage.
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Tight speed control linkage or cable.
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Vacuum line interference.
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Electrical harness interference.
NOTE:
AFTERMARKET GOVERNORS, THROTTLE LINKAGE AND CABLES ASSOCIATED WITH POWER TAKE-OFF UNITS, MAY
ALSO INTERFERE WITH PROPER THROTTLE RETURN. SERVICE AS NECESSARY.
6.
It is extremely important that all systems related to the engine and emission systems operate properly.
a.
Visually inspect the engine compartment to make sure all vacuum hoses and spark plug wires are properly routed and securely
connected.
b.
Inspect all wiring harnesses and connectors for insulation damage, burned, overheated, loose or broken conditions.
c.
Verify proper operation of the thermactor system. Thermactor systems that fail to dump thermactor air to the atmosphere properly or at
the correct time can cause high catalyst temperatures.
d.
Visually inspect thermactor system for damaged or kinked hoses and perform a function test on following components: air control valve,
check valve, silencer, filter and the air bypass solenoid.
