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diagnostic tools

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 84k5, May 6, 2004.

  1. 84k5

    84k5 1/2 ton status

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    Doin a tune up soon, and was wondering what kind of tools everyone has?

    I already have a timing light.

    My truck doesn't have a tach, what do you guys use to set idle speeds? Just 'feel'??

    Same for air/fuel ratio. You guys use some fancy tool, or is there a way to get it right without????

    TIA

    The 305 should be a champ in no time. /forums/images/graemlins/grin.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  2. lukebaby1

    lukebaby1 1/2 ton status

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    If your carb allows adjustment of air mixture. The best way to do it, is with a vaccume gauge. Tie in directly to your manifold vac behind the Carb, and adjust at idle with the vaccum advance plugged off. Your ideal adjustment setting will be the highest possible vaccume you can acheive on the gauge. /forums/images/graemlins/thumb.gif
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    You can do the same thing with a cheap tach. Adjust for max rpm while adjusting idle mixture screws. There is a Craftsman diagnostic box thing that has built in tach, dwell, and such like for the older trucks. It wasn't too expensive and worked ok. Years ago I had one that came in a kit with timing light, remote starter, compression tester, and so forth. You can also get a cheap tach on sale to hook up under the hood (temp or permanent) just for tuning.

    Generally I did it by ear on most pre CC engines.

    For those with TBI and a laptop, I recommend looking at WinALDL.
     
  4. 84k5

    84k5 1/2 ton status

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    Great! I found what you guys were talking about at sears.

    Next question: Checking for vacuum leaks

    I've been told to spray around the carb with carb cleaner, and the engine will stumble if I've got a leak.

    Is this the best way, or??? /forums/images/graemlins/ears.gif

    TIA /forums/images/graemlins/grin.gif
     
  5. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Best way in my mind would be a vacume gauge to start with to establish a base line. Then a careful visual inspection of every rubber line and coupler, throttle plate gasket, modulator line (check the jumper tube at the bottom too), vacume booster and grommet, etc. If the gauge reads low, I disconnect and plug all externals at the intake. Remove variables like modulator, AC control, and vac booster in case they are leaking? Check gauge again. Still low? You can spray ether, cleaner, WD40, or similar around suspect spots. And it doesn't stumble, it should settle down and or pick up rpm a bit since the spray is highly combustible which helps correct the lean mixture. Others use shaving cream which will help seal off a leak when it hits the right spot (or get sucked in if it’s bad enough /forums/images/graemlins/eek.gif), and a hundred other “old hand” tricks. Still nothing? Run a compression test and check the butterflies of the throttle plate (carb or TBI). Still nothing? Recheck and hope you missed something. Otherwise it may be internal and you have to start looking deeper for more indicators.

    That’s all that I can think of for now…
     
  6. 1-ton

    1-ton 1/2 ton status Premium Member

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    I have used the carb cleaner method to find vacuum leaks. What will happen is that when the carb cleaner is sprayed on the area that has the vacuum leak the engine RPM's will go a little higher because it is like giving the engine gas. I MUST WARN YOU, the carb cleaner method is not a safe method for finding a vacuum leaks. If you have a spark plug wire that is arcing with an open spark, then KABOOM!

    A vacuum gauge can be used to tell you if you have a vacuum leak, but not where the vacuum leak is. If your engine has a vacuum leak, then vacuum gauge will fluctuate wildly by a full inch of vacuum or more. A half-inch of vacuum fluctuation is not too abnormal, especially if you have a performance camshaft in it.
     
  7. Thunder

    Thunder 3/4 ton status

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    I use water in a spray bottle to find vacume leaks. Its non flamable and the safest way. Engine rpm will drop when it sucks in a little water.
    Spraying flamable liquid on a hot engine can cause it to spontainously combust resulting in a nice little fire.
     

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