Question about 1992 GMC G2500

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My 92 GMC 5.7L truck failed Wa State idle emission test HC limit of 220 with 320 reading at 680 rpm,,,,However, It passed cruise emmision at less than 50% of limit.... How do I lower the HC at idle? Is there any mixture adjustment on the down-draft fuel injectors,,,,,Is there an adjustment screw to increase the idle speed so the V8 does not lope? Thanks for any tips! Dave in Spokane

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I would go to the pharmacy and buy a half gallon of 75% or better isoprople alcohal the run the vehicle to almost empty,then add the alcohal and put just a few gallons of high test in it then drive to your testing station and get tested again after engine is warm.Afterwords go and fill it with more gas.Remember the more alcohal the betterbut no more than a gallon the the mix.It worked for me in ct with a 79 muscle car malibu and my numbers were of the charts.

Posted on Jan 31, 2010

Testimonial: "It worked! I used 36ozs of Iso-alcohol from "Heat" in my tank of 4 gallons premium gas. The idle HC dropped from 320 to 150 and it passed!! Thanks!!"

  • mike watson
    mike watson Feb 04, 2010

    Glad to hear it worked

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1 Answer

I have a 92 Caddy with a 4.9 that fails the PA


Sea foam, then run 99% alcohol through when it is time to pass emissions. Make sure the car is hot so take it directly after hopping off the interstate.

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What does No ppm mean?failed e-test


Here is some info for you to read, besides me explaining what ppm is, i also gave you some info of how to solve this, Ain't that special LOL. Mike

Overall Result: PASS or FAIL. A vehicle with a properly operating engine and catalytic converter will have very low HC and CO readings. However as a vehicle ages the HC and CO emissions will increase and may become erratic. As a vehicle ages it becomes increasingly important to be sure that the engine and converter are fully warmed up before the test to have the best chance of passing the test.

HC (PPM): The parts per million of hydrocarbons (unburned or partially burnt gasoline) in the exhaust.

CO (%): The percentage of the exhaust that is carbon monoxide (CO).

CO +CO2 (%): Complete combustion in the engine or catalytic converter will result in very little carbon monoxide (CO) and a high percentage (up to about 16%) of carbon dioxide (CO2) in the exhaust.

O2 (%): When there is complete combustion in the engine or catalytic converter there is a very little oxygen (O2) in the exhaust. Usually less than one percent. A higher reading indicates a problem with the engine, the exhaust system, the sampling system or the catalytic converter. Vehicles do not pass or fail because of the O2 reading; it is only diagnostic information.

RPM: The engine speed in revolutions per minute (RPM) or N/A.

Cruise Limit: The maximum allowable HC and CO emissions at 2500 rpm. The CO+CO2 (%) must equal or exceed 6. This verifies an adequate sample of the exhaust has been obtained. N/A for O2 and RPM.

Cruise Emissions: The emission readings measured at 2500 rpm.

Cruise Result: PASS, FAIL or N/A.

Idle Limit: The maximum allowable HC or CO emissions at idle. The CO+ CO2 (%) must equal or exceed 6. This verifies an adequate sample of the exhaust has been obtained. N/A for O2 and RPM.



These are the possible problems:

bad o2 sensor
bad EGR valve
bad cat
bad timing
dirty injectors
bad plugs or wires
the less costly fixes include replacement of the o2 sensor and EGR valve i would not clean the EGR I would buy a new one there are very cheap you can pick these up at any local parts store .
also run some injector cleaner through your car at least a full tank of gas and one bottle of injector cleaner should be ran through.
you can also have your timing checked for a relatively low price.
and when you go into to have the vehicle checked make sure the car is been running because your cat convertor has to be warm in order to preform at it peak so do not do it when the car is cold.
all of the above are pretty reasonable fixes the general rule of thumb when you work on your own vehicle is start with the cheapest fix first then go on to the next.

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2 Answers

My 92 Honda won't pass emissions at the higher RPM


Sell the car to somebody in FL, no inspection. The state realized it was a total waste of money. Anyway, it probably is the cat, you have 3 or 4 O2 sensors, maybe more. The cat is shot, Just take out the cat, park the car in the street, Call the police in the morning and tell them somebody stole your cat. happens all the time, they go right down the road and cut out 100 cats a night, for $50 each, I don't blame them. The insurance co will buy you a new one if you have the right coverage. If not, you will have to buy a new one, because you can't use an old one. But you can sell the old one on ebay for $50. They are expensive to buy. Hope this helps.

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1 Answer

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i would say change the O2 sensors and a new cat ,these readings are well over the top ,could have a exhaust blow on exhaust as well which will throw out the O2 readings

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1 Answer

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1 Answer

FAILED EMISSIONS


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Did you change the air filter. The fuel filter will have no impact on emmision's but the air filter is a very common problem.If you usually drive it at low rev.'s then before you send it for emmisions test you will need to put it in a low gear and floor it for about a mile the reason is when it is being tested the engine is reved up to around 3500 rpm and any build up of unburned fuel or oil in the exhaust system will put up the emmisions reading.

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3 Answers

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Hi Don,

First, thank you for asking me for my input on this. It just so happens, that I used to own a Ford ranger that had the same engine as yours. It was a 1990, but there are few changes to these model years.

Anyway, there is only one reason that your HC levels would be high. Your engine has WAY too much unburned fuel in the exhaust. The same reason applies to high CO levels. Too much fuel and/or not enough air.

Below is a link that you may find very helpful. It explains exactly what we are talking about here and also lists some of the possible causes.

EMISSIONS ANALYSIS

Incidently, when I had the same emissions failure on my truck, replacing the air filter and replacing a failed MAP sensor fixed it. - I did NOT have to replace the catalytic converter. If the numbers are as high as you listed above, you will only destroy a new converter anyway because there is obviously not enough oxygen in your exhaust system for the catalyst to function properly. Those numbers are nearly DOUBLE the allowable maximum. If the engine is running correctly and the catalyst is good, your numbers will be WAY BELOW those maximum numbers.

Please understand that I am NOT telling you to replace your MAP sensor without proper diagnosis. There are many possible causes here. Please click the link above and read the article. It will help you to understand what is going on here.

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3 Answers

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have you had the the engine codes pulled and reset?
and if so what are your engine codes?
i dont know of any car that will pass emissions test with the engine light on.
we cure your trouble that caused your engine light to come on and you will pass your test.
later
paul

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