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DTC 41, 42, 91, 92, 136, 137,139, 144, 171, 172, 173, 175, 176, 177 & some Possible Causes for Rich & Lean HEGO
The engine temperature must be greater than 50°F (10°C) to pass the KOEO Self-Test and greater than 180°F (82°C) to pass the KOER Self-Test. To accomplish this, the engine should be at normal operating temperature
next;
O2 Location Diagram & Depiction in 87-91 (from Factory Manual and the Ford Electrical & Vacuum Troubleshooting Manual (EVTM) - PASSENGER SIDE on EXHAUST PIPE from EXH MANIFOLD
Source: by Broncobill78 (Dave) at Ford Bronco Zone Forums
http://broncozone.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=6665
DTC 41, 42, 85 OR THREE DIGIT CODES 171, 172, 173, 179, 181, 182, 183 & 565 are received, Check for proper HEGO Ground;
in No power - exhaust restriction 86-91 E (91-12-11)for 86-91 Bronco, F Series, & Econoline (Catalytic Converter Diagnosis)
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.
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.
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.
Ground Location in an 89: "...it's not near the sensor. It sticks out of the loom of the wiring harness that traverses the back of the engine. You can find it by putting your hand around the loom and following it across the back of the engine. It is orange, has a ring terminal end and bolts to the middle of the intake in the rear
You can also use a mirror. I had to lay on top of the core support to reach mine. Trust me it's there. It serves only as a PCM ground for the O2 sensor. It isnt hooked to the sensor, it comes out of the PCM..."
Source: by j. r. Nice (J. R. N)
If the body looks clean, and the electrical connector is fully plugged in (may want to pull it apart and reconnect just to be sure it's clean),
If the HEGO ground is good, the following areas may be at fault:
Ignition Coil
Distributor Cap & Rotor
Bad or disconnected Spark Plug Wires
Fouled Spark Plug(s)
Dirty Air Filter
Stuck Open Injector
Fuel Contamination & Dirty Engine OIL
Intake Manifold Leaks
Exhaust Leaks
Fuel Pressure
Poor Power Ground
Engine Not At Normal Operating Temperature
BAD HEGO Sensor
Spark timing that is ******** from specification may increase exhaust gas temperature and shorten catalyst life. Refer to the following procedure for service details.
Check spark timing. Check base timing with SPOUT disconnected. Set base timing to the specification on the vehicle emission decal. See my site for timing
& note this;
Timing Procedure Manual Update TSB 90-18B-2 for 84-90 Bronco F Series, Econoline, Ranger & 86-90 Aerostar; May Exhibit Spark Knock/Ping after Starting Engine w/Remote Starter; Start Wire S Terminal Disconnected at Starter Relay with the Key On Will Cause the TFI-IV ICM to Revert to Start Mode Timing after the vehicle is started (Timing Will Be ********). Ignition Timing will be Incorrectly Advanced if Base Timing is Set while the Module is in Start Mode. Engine must be started w/the Start wire connected, using ignition switch to correctly set the base timing.
Source: by GENCO
Adjustment in Ford EFI Engines; MIESK5 NOTE; 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°. Use the ignition key only to start the vehicle. Attaching a remote starter might disable or initiate the start mode timing after the vehicle is started..." READ MORE
Source: by Ryan M (Fireguy50) at
http://oldfuelinjection.com/?p=71
Check computed timing with spout connected.
NOTE: COMPUTED TIMING IS EQUAL TO BASE TIMING PLUS 20° BTDC ± 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.
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.
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).
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.
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.
It is extremely important that all systems related to the engine and emission systems operate properly.
Visually inspect the engine compartment to make sure all vacuum hoses and spark plug wires are properly routed and securely connected.
Inspect all wiring harnesses and connectors for insulation damage, burned, overheated, loose or broken conditions.
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.
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.
Verify proper operation of the engine cooling system thermostat
also see this by Fireguy50 (Ryan M)
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DTC 77 system failed to recognise brief WOT dynamic resistance test. Need to press gas pedal during KOER; Operator didn't execute WOT when told to during self test
