Subaru Legacy 2.5 Quad Cam misfire

[cbrannan]

Can anyone help? I have a '96 Legacy 2.5 Quad Cam. It starts well, accelerates well but is jerky when trying to cruise at say 50-60-70 mph. When I put the slightest pressure on the accelerator the misfire goes away. It seems fine on a trailing throttle also. Sometimes the idle is poor and it can cut out at junctions, traffic lights etc, a blip on the throttle cures this. I have recently changed the mass airflow meter and the spark plugs. I did recently run out of petrol but it had all these symptoms before that. I had thought it might need a fuel filter? Under acceleration the car is a joy to drive, it's just when cruising I have the problem. Another thing is the fuel consumption, I know these cars are a bit thirsty but mine is particularly heavy, I think I'm getting around high teens driven easy. Another thought, one of the cat's is rattly........

[ScoobieWRX]

Sounds like the front O2 Sensor is buggered With no AFR readings the ECU is struggling to keep it in closed loop mode for idle, light acceleration, and cruise hence the rough running.

As soon as you put your foot down the ECU goes into Open loop and reads fuelling straight from the Primary Open loop fuelling map and everything is well.

Change the sensor, go through the process to reset your ECU, and you're away.

[GravelBen]

Sounds right - if the reason for you changing the MAF was the previous one failing then that may have caused overly rich running which IIRC can kill O2 sensors.

[cbrannan]

Thanks guys, where do I find this sensor? Are they expensive? How easy are they to change out?

[cbrannan]

what I actually meant is where on the car do I find it?

cbrannan said:

Thanks guys, where do I find this sensor? Are they expensive? How easy are they to change out?

[ScoobieWRX]

You should be able to find a sensor on eBay for a decent price. Equally talk to your local Subaru stealership and get the part number off them and see how much they want for one. Should be the same O2 sensor for a V1/V2 Classic Impreza. Even a used one will do. I've had a used one on for 2yrs and absolutely no probs. Most subaru's will generally only go through 2 sensors in a lifetime.

You'll find the sensor living at the end of the exhaust manifold, where it joins to the uppipe. You'll need a 22mm open ended spanner, proper O2 sensor socket or if it's properly welded in, a big pair of Stilsons or Mole grips to get it unscrewed.

Unplug the O2 sensor from the loom and undo the bracket that bolts onto where the spark plug retainer bolts to the head so the whole cable is free and hanging down so when you start to unscrew the sensor the cable turns with it, otherwise it's a pain to unscrew the sensor when the cable is twisted.

HTH