This document provides troubleshooting steps for excessive fuel consumption and a strong fuel smell in a 1999 Toyota Prado (90 Series) with a 3.4L engine. The original poster was attempting to replace the upstream oxygen sensor (O2 sensor) but had difficulty locating it.
Problem
- High fuel consumption (16-18 liters per 100km in suburban driving).
- Strong unburnt fuel smell from the exhaust.
- Mechanic unable to locate the upstream oxygen sensor (O2 sensor).
Solution
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Verify Oxygen Sensor Presence: Check the diagnostic plug in the engine bay (right-hand side, near the intake). Look for a pin marked for the O2 sensor. If the pin lacks a metal terminal, the vehicle likely does not have an oxygen sensor installed. Some early models in the light commercial range were not required to have them.
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Timing Belt Check: Inspect the timing belt to ensure it hasn’t jumped any cogs. A jumped timing belt can significantly impact engine performance and fuel economy.
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Spark Plug Inspection: Check the condition of the spark plugs. Ensure they are in good condition. Dual electrode spark plugs were originally specified by Toyota to improve spark plug life.
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MAF Sensor Inspection: Inspect the MAF (Mass Air Flow) sensor and ensure that it is working correctly.
Other potential issues:
- Injector Overhaul: Consider an injector overhaul to improve fuel delivery.
- Knock Sensor Harness Repair: Check and repair the knock sensor wiring harness.
- Power Valve Removal: Removing the power valve from the first muffler.
- Timing Belt Change: Perform a timing belt change if due.
- Automatic Transmission Service: Consider servicing the automatic transmission.
Relevant Parts
- Aftermarket RAE Oxygen sensor from Repco (potentially not required).
- Spark plugs (Toyota recommends dual-electrode type, but ensure good condition).
This technical summary was auto-generated based on recovered archives. Do not rely on its factual accuracy. Refer to the original thread. Source: View Original Conversation
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