I just got a 2.5" exhaust and magnaflow muffler put onto my 2.8 litre NA Hiace (3-L engine). The exhaust replaced a leaky stock 2" system back of the 18" front pipe. The old system had a cat that was probably plugged. Diesel soot was getting into the air intake from under the van - from holes in the muffler, even a hairline crack in the flange where the EGR pipe joined the dump pipe. ABC muffler fixed that one gratis. I also blanked off the EGR.

Performance is a lot better: 8-10% increase in top and cruising speeds, better mileage too, black smoke is now about a third of what it was, strangely.

The only problem I notice is that the engine gets lurchy and jerky when I gun it and it gets to 3800-4200 rpm, and then sometimes cruising at 2200 around 70 km/h. At first it would only lurch & jerk around 4k, now it seems to do so in an increasing number of circumstances.

It did this only once before the exhaust job - when I was flooring it up an entry ramp with a half-warmed up engine.

The engine has 125,000 km on it, and was serviced by Outback 13,000 km ago - rebuilt injectors, valve adjustment. Compression tested and found excellent since then, throttle cable and throttle positon sensor found to be good, as was injection timing. New air and oil filters in the last 2,000 km. 15-50 Synthetic oil.

Seems like inconsistent mixture or something. Any ideas?