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Engine trouble

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by ymatt, Oct 17, 2001.

  1. ymatt

    ymatt Registered Member

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    My engine is playing up. It's a '78 350 V8 with HEI. The idle is OK, but when you rev it, it sounds rough, like it's not firing on all cylinders, and there is no power at all; zero acceleration. Feels like something is straining it, and it seems to be doing about 2MPG. One of the front brakes is rubbing slightly, but not enough to affect the engine this much.

    I recently rebuilt the carb (Holley), and as far as I can remember, I had tested the engine since reinstalling it (but did not drive the truck because I had no brakes), and it ran well. Sounded great and revved very quickly.

    I also recently fitted headers, new mufflers, new exhausts, new plugs, changed the oil, new oil filter, new air cleaner, and a new PCV valve, but the truck is now performing FAR worse than before, and something is very obviously wrong.

    The only fuel filter I can find is in the carb fuel inlet - a gauze type filter, but I cleaned that.

    I have not yet taken the truck for an engine tuneup/check, but I don't really want to drive the 20 miles or so with the engine running as it is.

    Can anyone tell me what the problem might be?

    Thanks.
     
  2. Stoopalini

    Stoopalini 1/2 ton status

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    Vacuum advance maybe? Sounds like a timing issue. I'd check the vacuum hose to the distributor. If that's good, start pulling one wire at a time and starting it up in-between to see if one of the cylinders is not firing.

    Good luck,

    Thomas.

    -- '84 1-Ton Blazer --
    When the goin' gets tough,
    the tough go 1-Ton [​IMG]
     
  3. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    You could have damaged the wires when changing plugs. Get a set and throw them on. They're cheap. Make sure you use some dielectric tune-up grease. It'll make it much easier to pull the boots next time. Would check all vacuum lines and possible replace the cap and rotor. (cant hurt)

    My .02,
    John

    <font color=blue>"When all else fails, read the instructions, or get a bigger hammer"</font color=blue>
     
  4. hammer

    hammer 1/2 ton status

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    Here is a little trick I learned from NASCAR. To check and see if all the cylinders are firing get a spray bottle or squirt gun with water in it and spray each header tube, with the engine hot and running and see if all the header tubes are "steaming hot". If one cylinder isn't it's the plug or wire.
     
  5. Smitty

    Smitty 1/2 ton status

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    I've never heard of anyone cleaning the in-carb filter, just replacing it. I doubt that it is having the effects you're describing on the engine anyway.

    Smitty
     
  6. SKI-'84K5

    SKI-'84K5 1/2 ton status

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    Had the same problem when i did a diesel gas swap and it turned out my friend reversed two of his 4 plug wires if it is backfiring also that may be it, HTH
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd agree, check wire order/condition/plug condition.

    FWIW, I got 20 minutes life from 2 out of 8 brand new Autolite plugs. So new plugs doesn't=no problem.

    Double/triple check plug wire order, and if correct, pull one plug wire at a time, while its running (try not to shock yourself) until you find one or multiple, that make no difference whether they are connected or not. Connect it if that cylinder is firing ok, and move to the next. That will isolate it to cap/plugs/wires.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  8. ymatt

    ymatt Registered Member

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    OK, turns out the distributor is totally screwed, pretty amazing the engine starts at all really. Not just corrosion on the contacts, but full of rust under the rotor, weight springs rusted through, a module wire has insulation missing; it's all in one sorry state.

    The distributor bolt was loose too, so the whole thing rotates, which would explain why the timing is off. Also looks like at least a couple of cylinders aren't firing intermittently.

    I'll get some new plug wires and rebuild the distributor.

    Thanks for the help everyone.
     

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