Parts for your 1987 Mitsubishi Pajero-Oxygen sensor

1987 Mitsubishi Pajero oxygen sensor – what’s fitted and why it matters

Based on the Mitsubishi Pajero/Montero Factory Service Manual (1983–1991), the Mitsubishi ASA parts catalogue, and Gregory’s Pajero 1983–1996 workshop manual, an oxygen sensor was fitted to most 1987 petrol Pajero models sold in Australia and New Zealand (typically the 4G54 Astron II with an electronic feedback carburettor and catalytic converter, as required by ADR 37/00 emissions rules). Diesel variants (4D55/4D56) of the same era did not use an oxygen sensor.

On petrol 1987 Pajeros, the oxygen sensor (often a single‑wire zirconia type) lets the engine management control the air–fuel mixture in closed loop, keeping it right on the money for the catalytic converter. That sweet spot helps fuel economy, reduces pinging, cleans up tailpipe emissions, and keeps the cat alive. When the sensor gets tired, it gets slow or starts reading off, and the ECU/carby control can’t trim the mix properly—cue higher fuel use, a bit of a lumpy idle, and a whiffier exhaust.

As part of regular servicing, it’s smart to treat the oxygen sensor like a consumable on these older rigs. For the early, non‑heated single‑wire sensors common to 1987 petrol Pajeros, replacement around 80,000–100,000 kilometres is a fair shout, or sooner if symptoms pop up. Many techs will test it first: at full operating temp, the sensor should rapidly switch voltage as the mixture is trimmed, a lazy, flat, or stuck reading points at a crook sensor. Also check for exhaust leaks upstream, brittle wiring, or dodgy connectors—they’ll all throw the mixture out.

When replacing, use the correct thread size and seat, and avoid contaminating the tip with anti‑seize or silicone. Most new sensors arrive with a suitable anti‑seize pre‑applied to the threads, if not, use a sensor‑safe compound sparingly and keep it off the business end. Snug it to the manufacturer’s torque spec, refit the plug with tidy routing away from heat, and if your Pajero has adaptive trims, disconnecting the battery for a few minutes can help it relearn. After a replacement, a short drive cycle at operating temp should have the system back in closed loop. Keep running it on good quality unleaded and fix vacuum or intake leaks promptly—both will shorten a sensor’s life.

• Common signs it’s on the fritz: rough idle, worse fuel economy, blackened tailpipe, hesitation on cruise, or an emissions test fail.
• Petrol models: usually one sensor near the exhaust manifold/downpipe, diesel models of this year: no oxygen sensor fitted.

FAQs

Did every 1987 Pajero have an oxygen sensor?
Most Australian and New Zealand petrol models did, to support the feedback carb and catalytic converter. Diesel models of the same year did not use an oxygen sensor. If in doubt, look for a small sensor with a single wire in the exhaust near the manifold on petrol variants, and check your engine code (e.g., 4G54 petrol vs 4D56 diesel).

Where is the oxygen sensor on a 1987 petrol Pajero?
On the 4G54 petrol, it’s typically threaded into the exhaust manifold or just downstream in the front pipe. Many 1987 units are a single‑wire sensor, some markets received a heated multi‑wire version. Trace the lead to a small connector near the engine bay harness.

How often should the sensor be replaced?
There’s no hard interval, but for early single‑wire sensors, 80,000–100,000 kilometres is sensible. Replace sooner if you notice rough running or poor economy. Stick with reputable brands that match the original spec and connector to avoid wiring dramas.