3rz backfiring Qn

[tb]

Dear all, I have a 1999 xtra cab with a 3rz (170,000km). I have had it for about 4 months problem free. I gave it a service last week, oil, oil filter, air filter and fuel filter. After that I went for a spin in some small dunes, no water just bounced around abit.

Once back on the road it backfired when gearing down and has done so ever since. It had never backfired before the service. I took it for a tune today to a mechcanic and asked him to have a look. Sure enough, out on the road when gearing down backfiring continues.

Any thoughts or advice would be greatly appreciated. I am no mechcanic so advice would be great. Also since beginning to backfire it also chugs and spits when i turn it off but then eventually dies.

What do you reckon?

[Lux_89]

Dunno about the chugging when shutting off... but usually backfiring is caused by an air leak, somewhere along the line... mine backfires a fair bick(crackles n pops) when decelerating... sure enuf my exhaust has a very minor leak near the extractor. Other than that i dunno.

[tb]

Cheers Lux_89.

Ill begin with having a look at the exhaust. Would an air leak near the fuel filter cause backfiring if air was getting in there?

[Sic Lux]

To the above no it won't. A leak there you'd notice as the fuel at the filter is under pressure so it'd leak everywhere. Does this engine get reved a fair bit or just chugged around, from chugging do you mean it's as if it want to continue running.

[berad]

when you shut down a motor, and it still tries to run (sputter and carry on)is usually pre ignition, but almost all 3rz's in aust run coils, pre ignition is common with dizzy type ignition especially points.

Back firing could be a million things, rich, lean, exhaust leaks, intake leaks, head problems like valves, ecu and a 11ty billion other things.

Is the air flow sensor post air box clean and/or is the wiring loom plug connected properly, air flow sensors reading false readings cause all kinds of problems.

Does the back firing sound like its coming from the exhaust or somewhere in the engine bay.

Could possibly be a coil pack that is not working properly, 3rz's have twin post coils with ignitors, i had a problem in one coil pack where 1 post was not firing strong enough and caused similar problems but did not cause the motor to splutter when turned off.

Is the motor running on gas by any chance, some 3rzs have had valve problems from running on gas.

[smaddock]

Running on is usually caused by a bloody rich mixture isn't it...? How's the fuel usage? If its worse than before, I'd say something is causing it to run very rich, as berad said check your air flow meter, or possibly fuel reg vacuum hose.

[tb]

Back firing is definitely from the exhaust. Siclux, I dont rev it to hard, it is my daily, when I ment "chugged" yes it trys to keep running.

berad, i will definitely be checking the air flow sensor post air box to see if ti is clean and/or is the wiring loom plug connected properly. (may have moved it when putting in the new air filter or got some dust on the sensor)

smaddock, seems to be running fine, not extra fuel usage.

Thanks for all the info. Will be investigating those things on the weekend.