Basic trouble shooting 101, won't start


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Posted by casebro on Thursday, February 06, 2003 at 4:52PM :

Too many new mechanics try either the shot gun approach, willy-nilly jumping from component to component, or they blame what they don't understand "I don't know how a carb works, it must need a new one", so I thought I'd try a 'trouble shooting 101' class:

Engines need 3 things to run: Fuel, Spark, Compression. If it won't start, it is missing one of those three, check each in turn:

Spark, remove a plug wire, push back the boot,stick it somewhere so the metal end will be within 1/4" of a chunk of motor. Crank engine, if you get a blue spark, IGNITION IS NOT THE PROBLEM. If you don't get a spark wok your way back towards the battery, checking each component for proper activity, you'll probably invest in a voly/ohm meter at this point in your carreer.

Fuel:, remove the air cleaner, look down carb with out engine running, give it the gas, you should see a squirt of fuel from the acclerator pump, if not you might have a fuel problem. Next try loosening the fuel line between the pump and the carb, you should get gas out even when shut off, if not try cranking , it should spray gas through a loosened fitting. If not, you have a fuel problem.

Compression: A bad valve or two, or poor rings seldom cause a 'won't start' situation, they'll only make it run rough or backfire. But a timing chain can ruin your day, especially on the v-8's that used plastic gears, they've been known to jump at less than 20,000. And sometimes they will get intermittant, and jump around until they are back to where it started, and truck will run good for a while. To check the chain, put a socket on the big nut in the middle of the front pulley, and rock the crank back and forth. You should be able to feel some slack, before the chain has to move the cam. A healthy chain will have less than 1/2" slack (at pulley rim), a jumped chain will have 1" or more.

Hope this use of bandwidth helps someone, Chris Case



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