Parts for your 1988 Mitsubishi Pajero-Oxygen sensor

1988 Mitsubishi Pajero oxygen sensor

Technical sources indicate the oxygen sensor is fitted to 1988 Mitsubishi Pajero models with electronic fuel injection (EFI) petrol engines, notably the 6G72 3.0 V6 ECI‑MULTI introduced around this period, but not to carburetted 2.6L 4G54 or 4D56 diesel models. This comes from the Mitsubishi Pajero/Montero Factory Service Manual (1988–1990) where the ECI‑MULTI (6G72) emission system diagrams show an oxygen sensor signal to the ECU, while the 4G54 carburettor and 4D56 diesel sections show no such component. The Mitsubishi ASA (Asia/Oceania) parts catalogue lists an oxygen sensor for 6G72 EFI Pajeros of the era and none for the carb or diesel variants. Haynes’ Mitsubishi Pajero/Montero 1983–1996 repair manual echoes the same fitment notes.

For EFI petrol 1988 Pajeros that do have one, the oxygen sensor is the little hero that keeps fuelling on song. It sits in the exhaust manifold or front pipe, sniffing the oxygen content in the exhaust and signalling the ECU to trim mixture on the fly. That closed‑loop control keeps the air–fuel ratio near stoichiometric for the catalytic converter to work properly, helps with better fuel economy on the open road, and smooths idle and cold‑start behaviour.

By now, any original sensor is well past its best. Narrowband sensors of this era (often single‑wire unheated, many replacements are 3‑ or 4‑wire heated) gradually lose response, leading to thirsty running, a sooty tailpipe, or a pingy, uneven feel. On a first‑gen Pajero, the ECI self‑diagnosis can flag an oxygen sensor fault, you can also back‑probe to see the signal sweep if you’re handy with a multimeter. As part of regular servicing, it’s smart to inspect the wiring and connector, look for any exhaust leaks upstream of the sensor, and consider replacement at roughly 100,000–160,000 km or every 8–10 years.

• Replacement tips: soak the threads with penetrant and crack it with a proper O2‑sensor socket while the exhaust is warm (not blazing hot). If the new sensor isn’t pre‑coated, use a tiny smear of high‑temp nickel anti‑seize on the threads only. Tighten to the workshop‑manual spec (around 30–40 N·m, check your manual). Keep the harness clear of the exhaust and don’t use silicone sealants near the sensor.
• After fitting: clear the ECU’s learned trims (battery disconnect, if applicable) and let it idle to relearn. If the Paj still smells rich or uses heaps more fuel than usual, recheck for vacuum or exhaust leaks and confirm the sensor’s earth and heater supply (for heated types).

If the vehicle in question is the carburetted 2.6 or the 2.5 diesel, an oxygen sensor isn’t used because those engines run open‑loop mixture control (mechanical carburetion or mechanical diesel injection) and don’t employ closed‑loop feedback via an O2 sensor.

Popular questions

Does every 1988 Pajero have an oxygen sensor?
Not every one. EFI petrol versions (like the 3.0 V6 ECI‑MULTI) use an oxygen sensor, while the carburetted 2.6 petrol and 2.5 4D56 diesel do not. A quick check: if yours is EFI with a catalytic converter, you’ll typically find a single sensor before the cat.

Where is the oxygen sensor on a 1988 Pajero?
On EFI petrol models it’s threaded into the exhaust manifold or the front section of the downpipe, upstream of the catalytic converter. This generation generally has just one sensor (no post‑cat sensor like later OBD‑II vehicles).

Can it be driven with a faulty oxygen sensor?
Usually, yes—but it’ll likely use more fuel, run a bit rough, and can overwork the catalytic converter. It’s best to sort it soon to keep the Pajero happy and your rego inspections stress‑free.