yo,
DTC 98 Hard fault present; Failure Mode Effects Management (FMEM) FMEM is an alternate system strategy in the PCM designed to maintain vehicle operation
should one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy will be initiated. The PCM will substitute a fixed in-limit sensor value and will continue to monitor the faulty sensor input. If the faulty sensor operates within limits, the PCM will return to the normal engine running strategy. Engine Running DTC 98 or 998 will be displayed when FMEM is in effect. The Malfunction Indicator Lamp (MIL)/Message will remain on when FMEM is in effect. The MIL will come on while the engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on for at least 10 seconds, then stay on as long as the fault causing it is present. If the MIL flashes quickly (less than 10 seconds), the MIL circuit should be checked for concerns. Refer to «Quick Test». In FMEM mode, the PCM is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the PCM uses an alternate engine control strategy to maintain reasonable vehicle operation in spite of the fault. The DTC associated with this fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and the vehicle will return to the normal vehicle strategy. The DTC stored when the light was on is kept in Continuous Memory for the next 80 warm-up cycles (40 cycles on some applications) and then erased. This Continuous Memory DTC can be accessed by running the Key On Engine Off Self-Test. It should have some code(s) come up that will help narrow this down.
DTC 41
LIGHT TRUCK: 1986-91 BRONCO, ECONOLINE, F-150-350 SERIES
1988-91 F SUPER DUTY, F47
ISSUE: Lack of power or a no start condition may be diagnosed as an exhaust restriction caused by a plugged catalytic converter. A plugged catalytic converter (internal deterioration) is usually caused by abnormal engine operation.
ACTION: Diagnose the catalytic converter to confirm internal failure. Refer to the Catalyst and Exhaust System Diagnostic Section, in the Engine/Emissions Diagnostic Shop Manual and the following procedures for service details.
SERVICE PROCEDURE
1. Lack of proper HEGO operation may cause, or be the result of a rich or lean fuel condition, which could cause additional heat in the catalyst. Perform self test KOEO and KOER, service any codes.
NOTE: IF TWO DIGIT CODES 41, 42, 85 OR THREE DIGIT CODES 171, 172, 173, 179, 181, 182, 183 AND 565 ARE RECIEVED, CHECK FOR PROPER HEGO GROUND.
If the HEGO ground is good, the following areas may be at fault:
* Ignition Coil
* Distributor Cap
* Distributor Rotor
* Fouled Spark Plug
* Spark Plug Wires
* Air Filter
* Stuck Open Injector
* Fuel Contamination Engine OIL
* Manifold Leaks Intake/Exhaust
* Fuel Pressure
* Poor Power Ground
* Engine Not At Normal Operating Temperature
* HEGO Sensor
2. Spark timing that is ******** 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. 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. Visually inspect the throttle body and linkage for:
* Binding or sticking throttle linkage.
* Tight speed control linkage or cable.
* Vacuum line interference.
* 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.
e. Verify proper operation of the engine cooling system thermostat.
Almsot same as above by Ryan M @
http://oldfuelinjection.com/?p=31
DTC 54; the Intake Air Temp (IAT), (Air Charge Temperature [ACT] prior to 1992) sensor out of range. This one could be due to the engine not being warmed up or suspect nbad connector, shorted sensor, harness.
This sensor has 5v supplied to it (Voltage Reference (VREF) is a conditioned regulated constant 5v DC power source supplied by the PCM}, and returns a signal voltage based on temperature. If voltage from this sensor reads above 4.6v, the PCM sets the code.
Overview & Testing; "...This measures the temperature of the air entering the engine. Which impacts the fuel ratio; the cooler the incoming air is the denser it is. Denser air can utilize more fuel, giving us even greater accuracy in obtaining our desired air to fuel ratio. Before you start blaming the air charge temperature sensor and replacing it make sure the rest of the coolant system is in good condition. All of the following items will affect the ACT; Coolant level, Radiator Fan, Engine Temperature..." READ MORE
Source: by Ryan M (Fireguy50) at
http://oldfuelinjection.com/?p=29
