1990 gmc 305 emissions problems


Old 09-28-06, 08:23 AM
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Unhappy 1990 gmc 305 emissions problems

i have a 1990 gmc sierra pickup and i am having an emissions problem with high hydro carbons at driving. i have changed the o2 sensor the cat the egr valve and there are also new plugs wires and distributor on the engine and it still will not pass the stupid test. i am wondering if anyone else would have any idea as to why it could be doing this... i was told by a mechanic that it could be a rick fule mixture or it might not be burning all the fule out of the cylinders. please someone point me in the right direction as to what i should do because i have almost as much money tied up in repairs as i have paid for the truck. By the way the truck has a 305 engine, automatic transmission and is 2 wheel drive, throttelbody injection
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Old 09-28-06, 09:45 AM
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An old shade tree solution. When it has about 1/4 tank of fuel go to HD or Lowes and get a gallon of denatured alcohol, dump it in the tank, now drive it 50 miles on the highway and take it immediately for the emmissions check, do not turn it off until you have to. Post back as to your results. Have a nice day. Geo
Old 09-28-06, 01:16 PM
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Another way is to simply drive in a lower gear (say DRIVE instead of OVERDRIVE) at a pretty high RPM (3000 +) for 1/2 hour or so. Most emission test centers are in somewhat congested areas and you have to just putt along to get there....engine needs to be blown out and run strong to clear up residuals.
Old 09-29-06, 09:12 AM
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does anyone else have any options that i can try?

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