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WOT problems

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Wingnutt, Mar 20, 2000.

  1. Wingnutt

    Wingnutt 1/2 ton status

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    I’ve got a problem that I’m hoping that somebody can point me in the right direction with. I’ve got an ’88 K-5 with a 350 TBI engine/auto combo with 90k miles that has a problem in WOT conditions. From idle thru over ¾ throttle, it pulls good for a 5000lb barn door; the problem is that last little bit of throttle travel. The engine goes flat at WOT. The tranny holds the gear the way it’s supposed to, but it doesn’t help because the engine just isn’t making any power until I ease up and the tranny shifts. I can hold the throttle at 4/5 of the way open and the engine pulls pretty good, but as soon as I floor it, nothing. At first I thought the exhaust was the problem because some dingbat choked it down to a 1 ½ single right behind the cat, and said cat was almost clogged. I replaced the exhaust with a 3” high flow cat, and a low restriction muffler with 3” in and dual 2 ¼ in out pipes (defiantly no restriction now), but that only helped slightly. I have run several bottles of good fuel injector cleaner thru it (this stuff is good, I have used it before and it has done great). This weekend I took it on a 500 mile trip and this problem drove me nuts. I’m wondering if the problem is in the fuel delivery system, (i.e.: the TPS, fuel filter, injectors, etc) the timing circuit, or the computer itself.

    HELP!!!!!

    TIA
     
  2. kim tate

    kim tate 1/2 ton status

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    I was trouble-shooting my TPS just last weekend. Grab your voltmeter. You'll find three wires (supply, sensor, ground) going to your TPS sensor. Do not disconnect. With the key ON but the engine not running, probe each wire. The supply wire should read a constant 5 volts. The ground will read zero. The sensor wire, at closed throttle, should read less than 1 volt (mine read .5 volts). Keep the voltmeter on the sensor wire. As you operate the throttle by hand (key on, engine not running) the voltage should climb at a steady pace to about 5 volts. If no voltaage is found at any wires, you have an open or short in the wiring harness to the sensor.

    Another way to check the range in the sensor wire is with a resistance check. Get an ohmmeter and hook it up to the supply and sensor wires. With the ignition OFF this time, slowly operate the throttle from closed to wide open. Look for any unusual change in resistance. The changes should be smooth as it increases from low to high. These are two quick and easy checks. My truck is a 1987. The values for your 1988 should not be different, as far as I know. I don't have that information. Best of luck.
     
  3. Blazer1970

    Blazer1970 1/2 ton status

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    If you haven't replaced your fuel filter lately, that could easily be the problem. Change it first, and then move on to other diagnostics if the problem persists.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  4. mudfanatic

    mudfanatic 1/2 ton status

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    I've got the same problem with a '77 K5, no computer, good high flow exhaust, new fuel filter, 350/350/203 and an Edelbrock performer 650 carb sitting ontop of an edelbrock performer manifold.
    '77 K5

    <font color=red>mudfanatic</font color=red>[​IMG]
     
  5. shaggyk5

    shaggyk5 1/2 ton status

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    did anyone else notics the strange little figures above? in the first post?

    shaggyk5

    aint nuthin in the world like a heavy chevy!!
     
  6. Blazer1970

    Blazer1970 1/2 ton status

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    Mybe your browser is not displaying the fractions in that first post correctly. It looks OK to me.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  7. delta9blazer

    delta9blazer 1/2 ton status

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    my '89 had what seems to be the same problem.
    culprit was the transmission, not engine performance. tranny isn't shifting properly, holding the gear too long. power starts to sign off around 4500rpm, you're just floating the valves past that. something went, took out something else, finally wouldn't shift at all.
    very expensive re-build later, problem is gone.

    <font color=purple>delta9blazer</font color=purple>
     

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