2004 Nissan Quest - Codes

Exhaust roar and p0300 random multiple misfire with rich bank 1 and lean bank 2

From another site:
When P0300 occurs, it should be fixed immediately as long term driving with engine misfires could cause consequential damage to your engine and catalytic converter(s). Many times, P0300 occurs when there are worn out spark plugs, spark plug wires, or a faulty ignition coil.

Time to take it in. Get your exhaust system fixed, get the misfire diagnosed and repaired, running with the misfire may have destroyed your catalytic converter, so expect to spend some $$$.


Maybe someone stole your catalytic convertor, or a damaged exhaust.

As @Purebred said, ignition misfire caused by any number of things, WHICH rich bank 1 code? WHICH bank 2 lean code? You have issues too numerous to diagnose here. See your friendly local independent mechanic.

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Consistent w/exhaust leak bank 2. The o2 sensor is telling the computer the o2 levels are too high, which could be caused by not enough fuel being injected, but in this case more likely b/c outside o2 is getting into the exhaust system via a leak. You’d think o2 couldn’t get in b/c the exhaust pressurizes the pipes, but there are brief periods in the engine cycle when outside air can get sucked in via a leak. It doesn’t take much outside-air-o2 hitting the sensor to confuse the computer. Could be something other than that, but in any event it will be near-impossible to solve until the exhaust system is air-tight. Just a fact of life for modern fuel injection system.