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.
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HOMESERVICE MANUALSJEEP1991CHEROKEE 2WD L4-150 2.5L VIN P MFIREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSYMPTOM RELATED DIAGNOSTIC PROCEDURESPOOR FUEL ECONOMY
1991 Jeep Cherokee 2WD L4-150 2.5L VIN P MFI
Poor Fuel Economy
1991 Jeep Cherokee 2WD L4-150 2.5L VIN P MFISECTION Poor Fuel Economy
SYMPTOM DESCRIPTION:
From an actual road test the measured MPG is noticeably lower than expected. At one time the fuel economy for this vehicle was at a greater average than current measurement.
SYSTEM OR COMPONENT TO CHECK ACTION
FUEL CHECK: - FUEL TYPE, quality and alcohol content.
- FUEL PRESSURE
IGNITION CHECK: - SPARK PLUGS:
Remove spark plugs, check for wet plugs,
cracks, wear improper gap, burned electrodes,
or heavy deposits. Repair or replace as necessary.
- IGNITION WIRES for cracking, hardness, and
proper connections.
- SPARK CONTROL operation.
- IGNITION TIMING.
COOLING CHECK: - For obvious over heating problems.
- Low engine coolant level and leaks.
- Water pump operation, loose belts
- Restricted air flow to radiator or
restricted coolant flow.
- Faulty or incorrect thermostat.
- Correct coolant solution - should be a 50/50
mix of anti-freeze (coolant) and water.
- Fan operation (electric or belt driven).
MECHANICAL - ENGINE/TRANSMISSION CHECK: - Transmission shift pattern.
- TCC operation. A "Scan" tool should indicate an
rpm drop when the TCC is commanded "ON."
- For proper calibration of speedometer.
- For dragging brakes.
- For proper tire inflation.
From an actual road test the measured MPG is noticeably lower than expected. At one time the fuel economy for this vehicle was at a greater average than current measurement.
SYSTEM OR COMPONENT TO CHECK ACTION
FUEL CHECK: - FUEL TYPE, quality and alcohol content.
- FUEL PRESSURE
IGNITION CHECK: - SPARK PLUGS:
Remove spark plugs, check for wet plugs,
cracks, wear improper gap, burned electrodes,
or heavy deposits. Repair or replace as necessary.
- IGNITION WIRES for cracking, hardness, and
proper connections.
- SPARK CONTROL operation.
- IGNITION TIMING.
COOLING CHECK: - For obvious over heating problems.
- Low engine coolant level and leaks.
- Water pump operation, loose belts
- Restricted air flow to radiator or
restricted coolant flow.
- Faulty or incorrect thermostat.
- Correct coolant solution - should be a 50/50
mix of anti-freeze (coolant) and water.
- Fan operation (electric or belt driven).
MECHANICAL - ENGINE/TRANSMISSION CHECK: - Transmission shift pattern.
- TCC operation. A "Scan" tool should indicate an
rpm drop when the TCC is commanded "ON."
- For proper calibration of speedometer.
- For dragging brakes.
- For proper tire inflation.
RENDER: 1.0x
NO RELATED
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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.