please help fuel problem

Discussion in 'General Chevy & GM Tech Questions' started by txtruck91, Aug 9, 2012.

  1. txtruck91

    txtruck91 New Member

    I have a 1991 chevy 1500 4.3L, it's failing the inspection for to much unburnt fuel. I replaced the ECT and it's still seems to be dumping to much fuel. smokes at start up and smells rich at idle. when i whent to go have the emissions done it's failing. I really dont want to just start throwing parts at it. what ever the problem is when it trips a code the light will only stay on for about 30sec even while driving down the road.

    Any idea at this point is good. post your thoughts i need to get this done ASAP. please help me im lost.
  2. Kady

    Kady Epic Member 5+ Years GMTC Chick 100 Posts

    Move to MA, anything before 95 doesn't need Emissions inspection.
  3. txtruck91

    txtruck91 New Member

    Well that's not a choice I have. I just replaced my o2 sensor. Let's hope that works.
  4. Chris Miller

    Chris Miller Rockstar 100 Posts

    You should still be able to pull codes on it, even if the light's off. They'll be stored in memory.
  5. PantheraUncia

    PantheraUncia Epic Member 5+ Years 1000 Posts

    Hi Many miles and is it fuel injected or carbureted? I have 216k on my 2000 silverado and my millage as dropped, I am thinking new injectors might help as the old ones can be pushing extra fuel into the cylinders.[h=3][/h]
  6. txtruck91

    txtruck91 New Member

    I have 375285 miles and it's got a TBI on it. I have looked at them and there is a steady cone of fuel from each one so not thinking that's the problem.
  7. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    Well, maybe that steady cone of fuel is exactly the problem. That's alot of miles and perhaps the injector is worn to the point of not being able to limit the fuel when needed. In any event it is running rich when it shouldn't. Is air filter good, fuel pressure right, temperature sensor good? All things that can cause to much fuel for the conditions.
  8. PantheraUncia

    PantheraUncia Epic Member 5+ Years 1000 Posts

    If your injectors are easy to get to; I would at least take a look at them, over time the gas and any gas treatments you put in your tank will eat away at the tips of the injectors making them bigger, so unless something is clogging the opening, technically more fuel is going into the chamber making the mixture rich in fuel.

    I found the fuel injector here, but you could probably get it anywhere, look at the pictures and see if yours are worn out or have bigger holes in the bottom than the one in the picture, it is for a TBI. (again, if they are easy to get to). injectors#
    Last edited: Aug 10, 2012
  9. txtruck91

    txtruck91 New Member

    im still lost with bigger problems

    I have just completed a full tune up and now my truck is running like it has a miss only at low rpm's with a load on the motor. only thing i can thank of is that the cat is not letting breath like it needs to. i was told today that the cata can cause it to fail emissions for to much fuel also.

    any ideas on this?
    Last edited: Aug 10, 2012
  10. Skippy

    Skippy Member 2 Years 100 Posts

    Unburnt fuel in the exhaust gasses is typical of open fuel injectors or bad O2 Sensors.

    Unfortunately, when you have unburnt fuel in sufficient quantities going IN to the Catalytic convertor, the fuel ignites and destroys the platinum catalysts. If that has occurred, you very likely have a crippled convertor. Look under the car and at the convertor. If the metal is blue, it's an indication (though not a guarantee) the convertor has significantly overheated as a result of the fuel igniting in the catalysts. Catalytic convertors operate by essentially using platinum to react with exhaust gases to reduce pollution. The catalytic convertor is designed to operate at very high temperatures, but NOT at the high temperature of burning fuel (which is something like 1400 degrees F.) The high temp of burning fuel destroys the catalysts in the convertor.

    On TBI systems, on which I've worked, the fuel spray (when operating correctly) is always a pulse. You can see the spray pattern distinctly. If you're getting a steady stream, the injectors are likely just worn out. Injectors operate with a solenoid and a valve the solenoid charges and when the electric field collapses, it creates a strong magnetic pulse that opens the valve allowing the pressurized fuel to pass through briefly. Worn injectors can either be stuck slightly open, or simply allow fuel to pass through (leaking) into the intake. Occasionally, this is caused by deposits, but most commonly, they're just worn out.

    If you replace the catalytic convertor without addressing the underlying problem, you'll burn it out again. And if you only replace the underlying problem, you'll continue to fail emissions, because the catalytic convertor isn't removing the pollutants (which can look like a rich condition).

    Hope this helps.


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