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code 21 backfire?

847 Views 6 Replies 3 Participants Last post by  wazzappenning
ive had a code 21 for a while (o2 sensor) but just decided to go with it and probably burn more gas. this is on the 1993 3.3 caravan. the other day it backfired (underhood).

then yesterday i cut it a little close on a left turn, instead of taking off, it felt like a stall coming, backfired a few times and then went. this is going to cause some trouble eventually.

so, this sound normal for a 3.3? i checked the wiring/harnesses, and was going to time it and then realized coil packs, confirmed with the haynes manual non adjustable timing.

change o2 sensor, or is there something else that interferes with the computer???
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that is the first place to start, i would verify fuel pressure as well.
My experiance with backfire thru the intake manifold is usually related to a Cam Timing or Ignition Issue.
thank you guys.

please correct my line of thinking here.

if i remember the carbed k car days correctly, i think carbon build up in the cylinders could cause it too.

so could a faulty o2 sensor have led to carbon build up over time running rich?

regardless i will start with the sensor
In order for a backfire to occur in the intake manifold on a MPFI engine an intake valve has to be open when ignition/combustion occurs.
That is usually the result of Cam/Ignition Timing, Valve Stuck Open, Cracked Distributor Cap, Crossed Ignition Wires, Induced Voltage into an Ignition Wire.

If you have a carbon buildup problem that is that bad that carbon accumulation on the intake valve is preventing it/them from closing I would think you would have other issues as well.
Also, if you have a carbon buildup problem like that a chemical is not going to clean it, the head will have to be removed.
yeah i dunno, with battery disconected to clear codes,

i rechecked the harnesses, pulled them, and plugged them back in. they looked nice and clean.

i put a wrench on the o2 sensor and actually got it to loosen a bit.

i left it like that and went to get a sensor, drove my delivery run, and still no 21 has come up. no more backfires so far,and runs better. kinda weird but it works so far.

if the code comes back ill do the sensor, but why fix it if it aint broke?

thanks for the help
sorry for the delay, wanted to say thanks. however the code/rough performance came back, i changed the sensor and its all good for the few last months.
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