Question about 1996 Toyota Avalon

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1996 toyota avalon failed emissions test high hydrocarbons and they keep rising 3rd test thus far failing at 15 mph portion of test the more i fix the worse it gets it is barely out of range

Before first test replaced catalytic convertor changed oil and cleaned plugs not of that much wear fairly new 11000 miles or so and car barely passed emissions but it did pass however was failed due to self test system not completed cycled pulled code was egr insufficient flow tested all that i could within reason my first time on an egr system problem boy what a tempermental system toyota has indeed cleaned complete egr valve intake manifold plenum throttle body etc. to new condition removed all carbon deposit/soot replaced air filter and put in 91 octane gas 2nd time failed at 15 mph test slightly high hydrocarbons mil activated paid 90.00 hooked it to a dyno supposedly? bad egr modulator oem replacement it did in fact have a tiny whole in diaphragm ran self drive test no mil from this point on failed again at 15 mph test cycle even slightly higher hydrocarbons than previously tested nitrogen oxides have declined to 0000 carbon monoxides steady o2 increased a little dont know if that means anything on the o2 all tests on 25 and idle passed and it passed the first time only **** mil messed it up for a fail result to begin with very frustrating am replacing oxygen sensors although there is no code prevalent nor pending ran some garaunteed to pass cleaner threw a tank of gas and going for oem plugs but not wires at this time i am running out of money i am also going to fill up with 87 octane rather than 91 this time i dont understand the more i do the worse it gets it is so close and car runs like a champ runs fast and jumps high a real trooper my dad 1 owner highway miles of 217000 total any advise encouragement direction experience GREATLY APPRECIATED thanks to all for your replies

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Have you tried Engine decarbonizing type foam to remove the excess carbon for the engine?

Posted on May 13, 2014


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SOURCE: 1995 Toyota Camry - Code 71 - failed emissions tests

replace the EGR switching valve and have the machanic clear the engine check light. I think it should help

Posted on Mar 31, 2009

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mccartlidge. are you serious?? high HC is the result of a headgasket problem??? do everyone a favor and dont give advice when you clearly dont know a damned thing about emissions. as far as solutions to your high HC output, someone else mentioned the possibility of a worn out cat along with carb problems and or a simple air fuel adjustment. this car if i remember correctly has a feedback carb which means it has an oxygen sensor and a mixture control solenoid on the car to fine tune the air fuel mixture. it is not uncommon to have a oxygen sensor not functioning at all or out of normal calibrated range. easy test for oxygen sensor(single wire oxygen sensor ) is to hook up a voltmeter at 0 to 1 volt range(positive lead to oxygen sensor wire, negative lead to any good ground source) and watch the voltage. a perfectly working system the signal should look like a wave constantly rising and falling from .9v-.1v. test at 2500 rpm as well as at idle on a hot engine.if the oxygen sensor doesnt rise and fall, add fuel(spray small amount of carb spray) into carb while at idle or high rpm and the oxyen sensor should go full rich(approx .8-1v) that is point 8(.8v) not eight volts. you will usually see a reading of .9v . if the oxygen sensor doesnt put out a rich reading than its no good. on the other end you can remove a vacuum line(brake booster hose, half way removed as to not stall the engine) the oxygen sensor should go lean which means around .1 volts. if the oxygen sensor does not respond correctly replace it. beyond that, the engine first and foremost has to run on all cylinders to run clean and efficient. if it has a missfire or dead hole that will cause high HC along with high CO as unburnt fuel is going out the tail pipe. i could go on and on about possibilities but figured i would give you a couple basics to go on. Good luck.

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Sounds like it's not getting enough oxygen to burn all the hydrocarbons and carbon. Change out the oxygen sensor. Hope that helps. Is the air filter dirty? It might even improve things enough if you just change that.

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