1991 4 runner V6 3.0 code 21 O2Sensor

Tiny
JERRY JOE
  • MEMBER
  • 1991 ALL OTHER MAKES ALL OTHER MODELS
I've had problems with valves burning on this engine in the past. It has 215,000 miles and recent valve job (15k ago). Getting a code 21. Seems that before I had the valve work done I was getting a 21 code that would come and go (usually went off during hiway driving). Then the code I began getting was the dreaded 52 code.

My question is: is it a problem with the valves again causing no combustion in one of the cylinders that can be causing the 21 code or is the O2Sensor bad and not sending appropriate adjustments to the injectors? Can a bad injector cause valves to burn? Or is there something else I can look at that might be causing an improper air/fuel ratio? I will probably end up getting a compression check done, but would like to know why these engines burn valves so much and is there anything I can do about it?

thanks
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Saturday, February 10th, 2007 AT 5:17 PM

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Tiny
RASMATAZ
  • MEMBER
Change the HO2 sensor-the one w/4wires ahead of theC/Converter.

Is your engine burning oil.
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Saturday, February 10th, 2007 AT 9:15 PM
Tiny
RASMATAZ
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Cooling problems in the engine itself can lead to valve sticking and burning if the operating temperature gets too high. Low coolant, a defective thermostat, a weak water pump, a radiator obstruction, a defective cooling fan or fan switch, etc. Can all make an engine run hot. This, in turn, makes the valve stems swell which may cause them to gall or stick in their guides if there isn t enough clearance. If the valve sticks open, it can burn or be destroyed if it smacks the piston

Valves can also run hot because of elevated combustion temperatures. Factors such as retarded ignition timing, lean fuel mixtures (often due to vacuum leaks), detonation (from too much compression or low octane fuel) or preignition (from hot spots caused by deposits in the combustion chamber or too hot a spark plug) can all play a role here. Likewise, exhaust restrictions such as a clogged catalytic converter or crushed pipe can make the valves run hot.
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Saturday, February 10th, 2007 AT 9:27 PM

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