Why Engine Won't Start

It takes 3 basic ingredients to make an engine run, and if you have an engine that will not start, then it is missing at least 1 of those 3 things. The 3 basic necessities are spark, fuel, and compression. There are quite a few different individual things that will cause a car to crank but not start. For this reason, you need to find out which system or set of systems is missing up. In other words, which of these three basic things are missing. You need to look into the engine for these things. Often this is not possible to do without special tools, but if your engine has spark plug wires, you can easily pull one loose to check for spark, which will be explained.

When the engine does not start, the first thing you need to do is check the fuel system for proper operation. This is easily done by spraying some starting fluid, gas, or other flammable liquid in the engine. You can either open the throttle and spray it in there, or spray it in a vacuum hose that is connected directly to the intake runners that et air into the engine. If the engine starts, then the problem is in the fuel system, and a bad fuel pump is a likely cause, so you would look into if the fuel pump is coming on, and building up the right amount of pressure, etc...

If the engine does not start when you spray the flammable liquid in it, then the problem is not likely to be in the fuel system and is probably going to be in the ignition system. To check for spark is easy on most engines, just pull a spark plug wire loose, and stick an old spark plug in it, while holding the spark plug to the engine block. Be sure to wear a glove so you don't get shocked, and have someone try to start the engine. If the spark plug does not spark, then there is a problem in the ignition system. If it does spark, then there is either going to be a problem with the firing order, or compression in the engine.

If the spark plug is getting spark or not, you need to check for compression in the cylinders. This is easy by pulling out a spark plug, and sticking your finger in the hole, and have someone try to crank the engine. The cylinder should build up enough pressure to push your finger off the hole. There is usually close to 150 PSI built up in engine cylinders on your car. If there is not any compression building up in the cylinders then you will want to make sure the camshaft(s) turn(s). If the camshaft does not turn then there is a possibility that valves could be bent in the engine, causing you to remove the head to fix them. If this happens it will be because the timing belt has broken.

Now you know what to look for, so you can find which systems are messing up in order to get your engine cranked up again. If you need to know specific information about your vehicle, be sure to see the repair manual, which you can usually find online for free.