Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSFORD1991RANGER 2WD L4-140 2.3L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTEMISSION CONTROL SYSTEMSTESTING AND INSPECTIONSYMPTOM RELATED DIAGNOSTIC PROCEDURESHIGH EMISSION LEVELSHIGH HC - AT HIGH RPM
1991 Ford Ranger 2WD L4-140 2.3L SOHC
High HC - At High RPM
1991 Ford Ranger 2WD L4-140 2.3L SOHCSECTION High HC - At High RPM
This condition indicates abnormally high Hydrocarbons with low or normal CO during cruise (2500 rpm).
POSSIBLE CAUSE ACTION
Electrical misfires Check ignition system
Vacuum leak Check vacuum lines and routing in
VACUUM AND VAPOR HOSE DIAGRAMS
Check intake manifold
and vacuum components
PCV malfunction Check PCV system under TESTING
PROCEDURES.
EGR malfunction 1. Check EGR system under TESTING
PROCEDURES. If OK, step 2
2. Check EGR electronic controls.
Refer to COMPUTERIZED ENGINE CONTROLS.
Initial timing incorrect Check Ignition Timing under
ADJUSTMENT PROCEDURES.
Incorrect Spark Advance Check Spark Controls (SCC).
Refer to COMPUTERIZED ENGINE CONTROLS
Verify vehicle remains in Refer to COMPUTERIZED
Closed Loop at steady throttle ENGINE CONTROLS for
(2500 rpm) and oxygen sensor Self-Diagnostic procedures
is working
RENDER: 1.0x
NO RELATED
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Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.