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Vortec 8100 Issue...

This is a discussion on Vortec 8100 Issue... within the GM Trucks forums, part of the Vehicle Specific category; Originally Posted by Tobynine9 It's not a clogged cat. You can feel a strong pulse on both exits just by ...

  1. #21
    its short but its skinny. jiveass's Avatar
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    Quote Originally Posted by Tobynine9 View Post
    It's not a clogged cat. You can feel a strong pulse on both exits just by walking past them.

    I'm starting to fear it may be a dying fuel pump.
    fuel pump is not far fetched....i know if 4 1999+ chevys in the last year that needed new fuel pump...one of which was my own...except for when mine went out, it was instant and i was cruisin on the hwy.

  2. #22
    Senior Member Tobynine9's Avatar
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    This is a quote from Manic Mechanic over on Diesel Place Forums in response to some posting a similar issue -

    I'll try to give you some help here.

    The full fuel pressure should be 55-62 psi. Where it is depends on your regulator assuming your pump can supply excessive pressure. For best performance the higher the better within tolerance. Upto 2003 the fuel pressure regulator is adjustable, it has a set screw right in the center. It can be hard to adjust after the years go by. Try spraying Pentrating Blaster into it and letting it soak first. It requires a small tamper-proof Torx bit, like T-10H or T-15H. Set yours at 62 if it falls on the low side.

    Check your fuel pressure setting with the engine at idle. Take the intake manifold pressure reference hose (the small vacuum hose on it) off of the regulator and then read the pressure. This is the maximum psi the regulator will hold with the pump running. If your wide open throttle pressure drops below this under load, as in running through 2nd or 3rd gear, you have a fuel delivery problem. Make sure you have at least a half a tank of fuel when checking this. Check for a restricted fuel filter or fuel line damage before changing the pump. Also clean grounds first.

    The MAF can definately be bad and not set any codes. It will be within range but not enough to set a CEL. I have to deal with that at work often. An oiled cotton air filter is often a cause of a fouled MAF. Obtain a plastic safe clean drying spray cleaner like brake cleaner or MAF cleaner and with the MAF off hose it down. Pay extra attention and time to the small hot-wires hanging between the poles. These are delicate so spray only and no foriegn objects, no Q-tips soaked in Kerosine etc. These wires run around 360* in operation so oil can be baked on and require several repeated sprays to wash away. Sometimes it can't be helped. If your long term fuel trims are always greater than plus or minus 8% you can suspect a bad MAF. A WOT acceleration from a stop should cause the mass airflow dispay (on a scanner) to increase from about 6-12 grams/second at idle to about 230 g/s or more at the time of the 1-2 gear shift. If not inspect for a restriction (intake and exhaust) and if none found replace the MAF.

    An easy way to check the cats for excessive restriction is to temporarily remove the pre-cat O2 sensors and evaluate WOT performance compared to before. If you notice a difference there's a problem. Not an "I think it's faster, I mean it's louder right?" more like an "Oh man that was it!" difference.

    Make sure all air ducting clamps are in place and tight at all times of normal vehicle use.

    If you don't know if your fuel filters clogged (try blowing through it) or you don't know how your plugs look (pull a couple out and look at them) then you are probably overlooking the most common reason for lack of power in this truck. Plugs only last 100K in EPA land, mine get swapped at 50K. Filters rarely last me more than a year. My truck runs though 4 times as much fuel as a car in the same amount of distance. Fuel filter usage reflects that. Slight restriction of a wet filter element is normal, have to really force your breath though it is indictive of a clogged element. Pour some fuel through a new one and blow through to get an idea of normal restriction.

    Vernon
    _____________

    My MAF is clean and my plugs, wires and filters are all good to go. Next steps will be to pull the O2s and see if the cats are clogged (maybe I'm wrong when feeling the exhaust) and then check the fuel pressure.

  3. #23
    Senior Member Too Fast's Avatar
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    ^^^Very informative, detailed troubleshooting advice written there. Do all those steps, and at least you will have eliminated those items as a possibility.

  4. #24
    Living the Dream LS1FirehawkWS6's Avatar
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    A similar problem happened to my boss' Bass Boat. It turned out to be a collapsed fuel line. The line appeared/felt fine from the outside. But once he took it off the motor, you could see the inner-liner pinched off (it separated from the insulator and collapses under vacuum.

  5. #25
    Senior Member Tobynine9's Avatar
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    it seems to have quit doing it...

    i let it sit for a couple of days and rode the moto instead - in spite of the heat.

    we'll see.

  6. #26
    Member NaviDyn's Avatar
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    Can you check codes? You can set random misfire, then you know it isn't a particular cylinder, but more like an issue that effects all like you were checking. Random missfire is P0300.

    If you have a contaminated MAF sensor, it might not set a code, but you can get a lean code. P0171 is lean.

  7. #27
    Senior Member Tobynine9's Avatar
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    The guys at the shop who are fixing the A/C condenser have been driving it with the scanner and diagnostic w/no results. I don't want to pay them any more than I have to so I think I'll pull the O2s and see if it runs better, i.e. plugged up cats.

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