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F.A.C.T.S |
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Fuel. Air.Compression.Timing.Spark All the ingredients needed for an engine to run. This is an old catch phrase used back in my day for solving all engine running problems. Come to think of it, it is still the ingredients needed to run an engine today. So if you have an engine not playing the game use this catch phrase to trace the problem down. Fuel. Check for fuel delivery. There are a few different approaches, depending on the configuration of your engine. For a carburetted engine, check that there is fuel in the carby. remove the air cleaner top, look down the throat of the carby and operate the throttle several times. You should see fuel being squirted down the throat of the carby. It needs to be a strong jet. If the squirt splutters then you may be out of fuel in the carby bowl. For side draught carbies it might be easy to remove the fuel line from the carby and crank the engine over. Fuel will flow from the line. Be careful where this fuel ends up, try and catch it in a suitable container and keep away from ignition sources. Fuel injected cars pose a bigger problem. Checking fuel delivery in some vehicles is quite difficult but what you really need is a fuel pressure gauge connected so you can observe the pump pressure. Unrestricted Fuel flow alone is no guarantee that you have sufficient fuel pressure to run the engine. By this I mean if you take the fuel hose off and turn the ignition on, fuel should flow from the line for about a second or two, then stop. For an injected car to work, the fuel must be under pressure. It is possible to have flow with no pressure. A simple way to get around this is to slowly clamp off the fuel line to offer a restriction to flow. If the fuel pump is in good condition then fuel will exit the pipe under pressure and squirt a longer distance. If this is what happens then you can safely assume you have fuel. Air This is simply implying that if sufficient air is not entering the engine then no combustion can take place as the mixture will be excessively rich and the engine may not start. So what can cause this problem. The most obvious is an absolutely filthy air cleaner element. Once it is removed presuming this was the fault the engine should now start, maybe not straight away as the cylinders and manifold may be saturated with fuel. Other causes may be that something has found its way into the carby or manifold and is obstructing the air flow. A mechanical fault may be the blame. Check that the valves are opening and closing. If the inlet valve does not open then the air can't get into the cylinder. Neither will the fuel. A simple way is to remove the distributor cap and check that the distributor is turning as you crank the engine. If it turns then the camshaft must be turning. Apart from that Air is usually not the problem. Excessive air can also cause a no start. Check intake manifold bolts and gasket condition. Compression. You have fuel and air entering the engine bores but is it being compressed. To have a major compression failure to the point the vehicle will not start is an uncommon occurrence. This sort of problem just won't happen overnight, it will gradually creep up on you. The most common cause of this sort of failure is that the camshaft is not turning. Either the cam belt is broken or the timing gears have sheared. You will pick this up when your checking for fuel on a carburetted engine. Since most fuel pumps operate from the camshaft it is then logical that no fuel will flow as the camshaft will not be turning. This also will lead to no spark and also you won't be able to time the distributor. Timing. This encompasses everything in the distributor, distributor cap and HT leads. Check the static timing of the engine. Make sure you have power at the coil and that the ignition points arc when opened (ign On) Rotate the engine until it is on the timing mark then check the rotor is facing on No.1 cylinder or the opposing cylinder. Check that the HT leads are fitted correctly according to the firing order. Spark The last step is checking for spark at the spark plugs. If you have a good spark plug spare then utilise it. Remove one of the HT leads and connect it to the spark plug. Ground the plug. I like to use a set of jumper leads for this. Clamp the lead around the plug base and connect the other end of the lead to the battery negative terminal. Place the plug where you can see if a spark occurs at the tip of the plug. Now crank the engine over and observe the spark at the tip of the plug. A crisp blue spark is good. A weak yellow spark may not be enough to fire the engine. Possible cause could be the coil, HT leads or crack in the cap or rotor button. So have a close inspection of these components and look for traces of arcing. Generally if there is a crack in the rotor or cap, the crack will be coloured black. The HT leads can be checked with an ohm meter. For every foot of lead allow a maximum resistance of 7000ohms for a carbon type lead. I cannot cover every conceivable problem here as there are many different configurations in engines to deal with. Using F.A.C.T.S will lead you to the problem. You do not have to do it in the order I have stated. Lets face it, most people have a rough idea where the problem may be so if you think it is spark that is your problem, go straight for that. If unsuccessful in solving the problem then move on to the next. If I was confronted with an engine that did not start and I had no history of what happened then I would probably go in this order depending on the configuration. Fuel, Spark, Timing Compression and then air. Fuel and spark I may do in reverse, just depends which one is easier to do first. |