As a whole, your car’s engine is pretty complicated. It’s full of hoses and valves meant to supply everything from gasoline to vacuum pressure. When it doesn’t start, it’s a huge bummer, because then the process of figuring out what to look for begins which is often a daunting task. However, there are three key components that an engine needs to start and run, and those three I will address in this three-part basic no-start guide. The first thing I will cover is Spark (the diesel folks out there are chuckling to themselves right now). Get your handy volt meter out and let’s get started.
Before getting started
Are there any Check Engine lights on? If so check that first, you can have your code checked at any local autoparts store, or pick up a handy code reader from eEuroparts. This guide is assuming your starter is cranking with plenty of battery juice and you do NOT have a CEL. If your car is just dead with no cranking or check engine light, the first thing to check is the battery power, and if the battery is showing a little over 12v, then make sure it’s making it to your starter. If there is no power to the starter, check for power at the ignition relay (labeled in your relay box), you may have a bad relay or ignition switch if there is no power in or out of the relay. It’s common to just pull the relay out and jump it with a piece of thick wire to bypass the ignition switch. If power is getting to the starter and it’s not cranking, then the starter solenoid could be burned out, or the starter motor is bad. If your engine is happily cranking, move on to the next step.
Finding Spark
The first (and easiest) thing to check to make sure you have is spark. To find if you have spark, you have to pull one of the spark plugs out, and attach the spark plug wire or ignition coil. In engines that use a coil pack or cassette this is a little more difficult but fundamentally they are all the same. Take a wire (or other piece of metal) and tightly wrap it around the threaded area on the plug that would be screwed into your cylinder head, this is your ground. Alligator clips will work best and will be the safest. Connect the ground to the engine or other metal part of the engine bay and have someone crank the engine momentarily. You only need to crank it a few times, the plug should be snapping away with a spark. Don’t crank it for more than a second or two to ONLY to verify spark, and BE CAREFUL as there will be 1000’s of volts coursing through the spark plug and your makeshift ground.
On a Direct Ignition Cassette, you will need to take a wire and connect all 4 threaded parts of the spark plugs together in series, then run that wire to ground or the DIC will not fire.
If you have done this correctly and observe a spark, then you will have to move on to the next step, fuel. If not, here’s some information you need to keep in mind.
Pre-OBD systems
In older cars, the ignition system was pretty basic and easy to diagnose. You need to check that the battery has power, the alternator is functional (not fried), your ignition coil has voltage in and out, and your distributor has voltage out to the plugs. Going down the line like this you can usually find an issue pretty quick with a volt meter. Wherever the power hits a dead end, that’s where you will centralize your focus on.
Modern electronic systems
In a modern car, the ignition system is controlled by an ECU/computer which makes things a little trickier. The ECU will only give the go-ahead on an electronic system with a few basic key bits of information. In general, this is is the Crankshaft Position Sensor, and in vehicles equipped with an automatic transmission, the Neutral Safety Switch (AKA Range Switch). Without the correct signal from both of these parts, the ECU will not get ‘the go ahead’ and it won’t fire.
Crankshaft Position Sensor
With a bad CPS, it is common for the car to run OK when cold, and not want to restart once warmed up as temperature has a much bigger effect on failing crank sensors. You usually will NOT get a check engine light for a bad CPS, although that’s not always the case. A bad CPS can also cause the car to run poorly as the ECU can’t adequately gauge the proper timing. That will result in poor fuel economy, sputtering, and other issues signalling inaccurate spark timing.
Neutral Safety Switch
The neutral safety switch is a sweeping switch hooked up to your shift linkage, generally located on the transmission. When you put the car in to Drive or Park, the contacts for those will touch and the computer will know the position of your gear selector. With a bad neutral safety switch, sometimes the car will simply stop starting with no rhyme or reason, and if you’re lucky you will get a gearbox fault light. If the ECU does not clearly see the car is in neutral, it will not risk starting the engine with the car in gear.
Issues with both of these parts can be found by plugging the car into a specialized scan tool that has some fancy things built in, dealers and independent specialists can usually check signal strength and continuity. Otherwise you can try the ‘throw parts at it‘ approach and replace the CPS and Transmission Switch. If your car has more than 100k miles on it, replacing the CPS might be a good idea to do anyway. The Neutral Safety Switch is usually more expensive, and a proper diagnosis might save you some money in the long run.
If you have anything specific to add that’s not touched on here, or you have a car that has components other than the CPS or NSS to prevent the ECU from supplying power to the coils, comment below! There are a lot of cars out there with weird or elaborate systems that can also cause a no-spark situation not mentioned here. Stay tuned for Part 2: Fuel, coming next week.
