Where to Start When Your Jeep Won't

Checking to Find Your Jeep Starting Problem

There's a multitude of reasons your Jeep will not start, some small, some big. But let's take a quick view of the bases to cover, to see if it's something that can be dealt with quickly. First, there are really two basic things you need to start a vehicle:

1. Spark
2. Fuel

Usually when a vehicle won't start, it's always one of those two. Let's begin with Spark.

Spark Is Important to Get the Jeep Engine Running

The most important part of spark is the battery. A quick hookup with a test light can tell you if it has any power. The bulb lights up? Then the battery still has at least some power left. Batteries use CCA (Cold Cranking Amps) to measure starting power. The battery itself is 12 volts. But CCAs are measured (by scientists) as the discharge load (how many amps) the battery puts out in 30 seconds, in a cold environment. (0° to -18°C). There is also a CA (Cranking Amps) measurement that is done at a higher temperature ( 0°C, or, 32°F). What this means is that a battery can still have power, but under load, the cranking amps are not there, or powerful enough to get the starter to overturn the engine. If your battery is old (5+ years or more), it could be the culprit. Most garages and auto parts stores have devices to test a battery, some can test it under load. Auto shops can test a battery while it's on the vehicle. As a note, if you don't live where the weather is freezing (0°C or 32°F), CCA's probably won't mater much to you. Your owners manual should mention the CCAs needed. It's important to make sure you use a battery with the correct CCA, as a CCA that is too low won't work well. To many CCs doesn't matter much unless you live where it's brutal cold weather, and will normally cost you more when buying a battery.

Pain and Jeep Battery Cable

If the battery checks out okay, then the next in line are the battery cables. There is a negative, and a positive. The negative typically bolts to the frame or engine. That contact needs to be clean, hopefully it's rust free. The positive goes to a starter relay / solenoid, which is before, or on, the starter. These can go bad over time, because of heat. In the old days, you could sometimes reach underneath and tap the solenoid with a hammer and it would function long enough for the starter to engage. Some battery cables have a large fusible link at the positive cables terminal at the battery. Those are to protect the sensitive electronic parts and computers on your vehicle. So if there's an unusual power surge, they pop. This also stops current from running down the cable, thus, that would prevent the vehicle from starting. A starter usually lasts a long time, even through thousands of starts. They do go bad over time though. On a Jeep, if your starter is constantly in the water, mud, dust and sand, it may develop issues early on. Most auto parts stores and garages have testers. A garage usually has the better one, because they can test the starter while it's on the vehicle. If the battery and starter are good, then getting the engine turned over is not an issue. Meaning, the engine is turning over, but the vehicle won't actually "fire up". Now it's time to take a peek under the hood. Just about every vehicle has a coil, or coils. On older models, a single coil sends power to a distributor, then the wires, and then spark plugs. Newer engines bypass using a distributor, and use coils to directly fire each plug. (Some car companies are already at work to eliminate spark plugs entirely). On older vehicles, a visual inspection of the coil, cap and wires can verify an issue. If you pull a spark plug wire off, and there's spark at the end, then it's getting power. There could still be an old "brain box" for the distributor, a kind of crude computer, those can go bad from time and heat. On a newer vehicle, where it's all computer controlled, all you can do is give the engine a quick visual look for anything abnormal, or any loose wires. But not much else (you would need a computer tester device to hook up to a diagnosing port). Note that the ignition switch (and tumbler) must be working as well. Jeep has had many issues with these parts as far as recalls. The ignition switch is the electrical part, the tumbler is mechanical. The switch sends momentary power to the solenoid for the starter to engage. Before you finish checking off these ideas above, check your owners manual for the fuse box. The manual should label which fuse goes to what. Check them. A blown fuse protects systems on your vehicles, and a popped fuse can possibly prevent the vehicle from starting.

You Need Fuel to Start Your Engine

The second thing you need is fuel. Sounds simple doesn't it? For the most part, it is. On older vehicles, the fuel pump was mechanical, and normally bolted to the engine block. They rarely go bad. Is it pumping fuel? Is there a fuel filter? Is it clogged? A mechanical pump put out about 7 psi, and that can be tested with a fuel pressure gauge. On newer vehicles, the fuel pump is in the fuel tank. You can't even see it. You can still test fuel pressure, but it will be around an average of 35 psi. Some cars have a switch in the back or trunk area in case of an accident. It will shut off the fuel pump as a safety feature (Lincolns come to mind). But a really strong jolt can activate that switch accidentally sometimes. In which case, it needs to be reset, so you can get started and be on your way. In many cases, the fuel pump in the tank (or on the frame rail, such as on some European and early EFI U.S. cars) activates when you turn the ignition. Sometimes, you can hear this pump come on if you are near the rear of the vehicle (and someone else turns the key in the start position). In some cases, you must also have the brake depressed before the pump will come on (as a safety feature - the joys of computer controls). Because electronic fuel pumps are usually in the fuel tank, they're not easily diagnosed, or replaced. But they do go bad. Note that gasoline keeps the pump cool. Ever stuck your hand in a bucket of gas? Notice how cold it is? The fuel sloshing around in the tank helps cool down the pump. If you run your vehicle near empty all the time, chances are, you're shortening the life of your fuel pump from heat. Note that fuel injected vehicles use fuel filters as well, and they should be unclogged, and replaced as regular maintenance. Again, always check the fuses. There is probably a fuse, and or a fuel pump relay to control the pump. Maybe a starter relay as well. A failure of either one will mean no operating fuel pump, no fuel to the engine, and no starting. Hopefully these tips will help you one day if your Jeep just won't start. It could be 100 other things than what we didn't mentioned here, but you have to start somewhere, and the basics are - fuel and spark.

What handy tips do you have for getting a dead Wrangler started?