A few things to keep in mind if your car won't start, runs really rough, or dies after it starts. It can help you trace the root of the problem:
- Getting an engine running needs three main things:
- To this, you can add having a starter to get the motor turning over in the first place
- Also in the fringe of this, you need compression to extract power from ignition.
- Things that can keep you from getting enough fuel into the pistons:
- You're out of gas.
- Add more gas.
- You've got bad fuel
- If the car has been sitting a long time, or you went to the wrong shady gas station that watered their gas, or added who knows what else to the gas, then your 'fuel' isn't going to burn like you want it to.
- You can try adding a bottle of Octane Boost from an auto parts store to see if that will have any effect. If it runs any better, try to run the tank fairly low before adding more gas, just to get as much crud out as possible before diluting it again.
- Your fuel pump is dead, leaking, or about to fail.
- Particulars here may need a good vehicle DIY guide or video to tell you how to check the fuel pump.
- Fuel pumps will usually have a fuse, and/or a relay. you may want to check that the fuse/relay is intact, to make sure that the pump isn't disconnected from power to run.
- There is a leak in a fuel line
- If you smell gas after trying to start the car, be very careful. A fuel leak can be very dangerous to kill you or hurt you badly. It should be tracked down and fixed ASAP.
- Your fuel filter is clogged.
- One of the more common villains. If you don't know how long it's been since the fuel filter was changed, and/or have no record of it, this is often an easy bit of maintenance. Look up the procedure, there is almost assuredly a video on Youtube showing you exactly how to do it.
- Your fuel injectors are clogged
- Start with adding a bottle of Fuel Injector Cleaner to a full tank of gas, and then, optimally, driving the car for at least a few tens of miles. If the injectors are really crudded up, it can take a while to have an effect. Most mechanics will have access to much more powerful injector cleaner than you can get at Pep Boys. It might be worth it if it looks like clogged injectors and the over the counter stuff isn't working.
- Things that can keep you from getting enough air to the piston
- Dirty Air Filter
- This is the most common culprit, especially if you may have been driving during smoky, dusty, or other debris-rich environments. Look up 'change air filter' with your vehicle make/model/year, and you'll find plenty of video or step by step guides. Most are easy to get to. See if there is a dust bunny colony living on the filter, or if it's clogged with oily gunk. In either case, it's best to install a new filter. if you haven't bought one yet, and it's just dust bunnies, you can bang the filter gently into a dustbin to get the worst dirt off, vacuuming with a crevice tool can work too. Don't try to wash the filter with liquids. Then put it back in until you can get another filter to replace it with. Don't omit the filter, you can ruin an engine really quick once you start letting dust and grit go unimpeded into the pistons.
- Valve problems
- This is getting quickly into the realm of leaving it to a mechanic unless you have some serious tools and DIY skills. Clogged or damaged valves can interfere with air coming in and/or exhaust leaving. Fixing that is way out of my pay grade.
- If your car is turbo or supercharged, a lack of air could mean a blockage, misfunction, open vent, or damage to the turbo or supercharge loop. Turbos and supers usually have an overpressure release valve to keep you from blowing up/out your engine. If the valve gets stuck open, then your input air has easier places to flow than into the engine.
- Airflow can also be blocked up if exhaust can't get out of the cylinder. Exhaust systems can be a pain to diagnose or check, and generally should not end up blocked unless it's at the very end of the exhaust. Check that your toddler hasn't stuffed a rubber ball or a banana into the tailpipe.
- Spark Problems
- There could be a problem getting electricity to the spark plug. Check that distributor wires are properly seated, that the wire to the coil, or coils, is/are properly seated.
- There is a usual interval recommended by the manufacturer to renew your spark plugs. Newer vehicles often have irridium plugs that can be run from 50K to, in some cases, over 100K miles. That said, if you're way past that time, it may be time to get new ones.
- The ignition system may have one or more fuses or relays feeding into it. Look at the fuse listing for your vehicle. if there are things listed like Electronic Ignition System, (the modern version of the distributor) haven't blown a fuse.
- If you pull a plug, look at the electrode area.
- There are a lot of different appearances and causes for plugs that don't look right. See, for instance
. Make sure you look at the plug gap. Many plugs for your vehicle these days will come pre-gapped, but check them with a gauge before installing.
I also mentioned the starter and compression:
- If the car won't even turn over, like there's a 'click' and no sound when you turn the ignition, then you need to start with a possible dead or worn out battery, connection problems to the starter, or a damaged starter. The starter will pretty much always have a relay used to switch the high current power to the starter solenoid and motor. Check the relay and make sure it clicks when you turn the ignition switch.
- Bad compression can come from worn piston rings or cylinder walls, worn/leaky valve heads, a head gasket leak, the spark plug not being screwed in to proper torque, or there being no oil lubing the piston wall/piston ring gap. The latter should be addressed by making sure that there is enough oil in the engine, that it's been changed within the last service interval, and that the oil filter was also changed and isn't so clogged that it's blocking oil flow. This is a really quick path to dead engine that can't be fixed. Never run the car if it's out of oil. Other than tightening the spark plug to the right torque, the other things like worn rings, valves, or piston walls are into the deep end of DIY. You'll want to carefully consider if it's worth the time and money to go fix all that stuff, especially since if, say, you get the valves re-done, but leave the piston walls/rings, you'll up the compression on top, and likely blow out either the rings or the head gasket soon thereafter.
These are just a small chunk of things that can bugaboo the engine of a car, but it covers a good chunk of easy and reasonable things to check that you may have a good shot at DIY fixing.