Engine Won't Start: A Troubleshooting Guide

[BusaDave9]

If your jeep won't start there are a number of things that could be causing the problem.
If your engine was running recently but won't today there are 3 areas to concentrate on:
1. Starting system to turn the engine over until it can run on it's own.
2. Fuel making it into the cylinders.
3. Spark igniting the fuel.

Now keep in mind there are several other things needed for an engine to run. Things such as air, compression and timing. You usually don't loose these things suddenly one day. As an engine ages the compression gradually lowers. It keeps running but performance goes down gradually. Air flow into the engine usually doesn't stop suddenly one day. Air is one of those things I assume your engine has. It is possible for a timing chain to jump teeth on the timing gear. This will cause the engine to run but run rough. If the timing chain were to break the engine would crank over but not start. It's uncommon for a timing chain to break.
For these reasons this thread will not be the end all for troubleshooting an engine that won't start. If you follow this thread and your engine still won't start please post a new thread and let us know what you already tried. And for the sake of sanity, please tell us up front any changes you made to your engine before it failed to start. We don't want to hear 6 pages into the thread “oh, didn't I tell you, I just replace my distributor the day before it wouldn't start?”

98% of all engines that were running recently but won't start today have a problem with one of these 3 areas: starting system, fuel or spark.

This troubleshooting guide can be used for any Jeep CJ engine. Actually it can be used for most older engines.

 

[BusaDave9]

Initial Troubleshooting

Initial Troubleshooting:
Narrow down the problem


If the engine was running recently but won't start today the problem is most likely one of these three things:
1. Starting system
2. Fuel
3. Spark

Okay, you sit in the drivers seat and turn the key to start the engine.
What happens?
1. The starter won't turn the engine. Maybe the engine turns very slowly, too slowly to expect it to start. Or maybe you only hear a clicking sound.
Okay, you have a problem with the starting system. You need to go on to the next post.Click Here to Troubleshoot a Starting System
2. The engine cranks and cranks. So now it looks like you either don't have spark or fuel. Continue on to step 3 to narrow down where your problem is.
3. Do you have a fuel problem? When someone in the driver seat pumps the gas pedal the accelerator pump in the carburetor should squirt fuel into the throat of the carburetor. If this isn't happening you may have a problem with the fuel system. Another test is to pour a small amount of gas down the carburetor throat.
Click Here to Troubleshoot a Fuel Problem If the engine starts but quickly dies it could be a carburation problem. In that case check to make sure the choke is working.
4. Do you have an ignition problem? We need to check for a spark. Get a spark tester. Here's a common type of spark tester:

Adjustable spark tester
​

If you are not getting a spark Click here to Troubleshoot an Ignition System

 

[BusaDave9]

Troubleshooting a starting system

Troubleshooting a starting system
The starting system is only responsible for turning the engine until the engine can run on it's own. This is a very simple system.
If the starter won't turn over the engine we should first check the battery connections. This is the most likely cause.
Grab the battery cable and try to twist it. If you can turn it with your hand it's too loose.
Remove the battery cables. Clean the battery terminals and cable ends. Then try again.

If your CJ still has OEM top post batteries use one of these battery terminal cleaning tools.


Battery cables can go bad but when they do it is almost always one end, usually the end at the battery and it is usually easy to see that it's bad.
To narrow down the problem we need to bypass the starer solenoid. This next test will only test the battery and the starter. This is high current so use a jumper cable. Have someone in the jeep turn the key to RUN. Connect the positive terminal of the battery to the end of the starter solenoid that has the large cable going down to the starter.

​

If this works and your engine starts then we know the starter solenoid isn't getting energized. Okay, now we know the problem is not the battery or the starter
Click here to troubleshoot when we know the Starter and Battery are good
If jumping the solenoid still doesn't work it indicates either a bad starter or a bad battery but before we go any further lets double check the connections. I already had you check the battery terminals but we need to double check them since corrosion makes this the most likely place for a bad connection. Also check the other cables. The battery ground cable should be bolted to the engine block. Make sure that is connected properly. The above test also bypassed the connection on the solenoid that goes to the positive end of the battery. Check that connection. Also check the connection on the cable that attaches to the starter. Okay, now we are sure the cables are getting a good connection. If jumping the solenoid won't start the jeep we know we have a bad battery or a bad starter. Continue on to the next post.

 

[BusaDave9]

Bad Battery or Bad Starter?

Bad Battery or Bad Starter?
Our troubleshooting has told us we either have a bad battery or a bad starter. Almost any automotive parts store can test either of these but lets continue troubleshooting to narrow it down more.

Charge the battery. We could use another vehicle to jump your jeep but if at all possible I would prefer we used an automotive battery charger. Disconnect the negative battery cable and charge the battery. When a good battery is fully charged it should read 12.6 volts BUT let me stress that a volt meter CAN NOT be used as a test to verify that a battery is good. To test a battery bring it to an automotive parts store. They can test its load capabilities. You could string enough flashlight batteries together making 12 volts but under load they will never be able to start your jeep. With a good charge on your battery connect it back up and try to start your jeep. If it starts, great, your jeep is fixed. Or is it? You need to ask yourself why the battery went dead. Did you leave the lights or something else on? If you are careful not to leave anything on and the battery goes dead again continue with the next post to find out Why your battery keeps going dead.
If a fully charged battery won't start your engine have someone in the drivers seat turn the key to start and tap the stater with a hammer. It it starts now then you have a bad starter. Remove the starter and have an automotive parts store test and replace it. It it still won't start the problem is your battery. Remove it and have an automotive parts store test it.

 

[BusaDave9]

Why does my battery keep dieing?

Why does my battery keep dieing?
If you often need a jump to get your engine started there are 3 likely causes:

• Bad Alternator
• Bad Battery
• Short draining the battery

When your engine is running the alternator should be putting out 14 volts (give or take half a volt). To check this voltage put the negative lead of your volt meter on the negative battery post. With the engine running put the positive lead of your volt meter on the nut holding the large red wire on the alternator. Give it a little gas to raise the engine to 1200 rpm. If the voltage is low and won't raise to 14 volts when the engine is at 1200 rpm you have a bad alternator. There is a chance that you have a short that won't allow your alternator to reach 14 volts but that is unlikely. A alternator should be able to put out over 75 amps. It would take a bad (very high current) short to prevent the alternator from putting out more than 12 volts.

If your alternator puts out 14 volts when the engine is running but your battery still dies after the jeep sits for a while you could have a bad battery. Remove the battery and bring it to an automotive parts store to be tested or replaced.

Okay, so you know your alternator and your battery are both good but your battery still goes dead after the jeep sits. This could be a short circuit that is draining your battery when your jeep is sitting. A short circuit is often hard to track down. With the engine, lights and everything else off, disconnect the negative battery terminal. As you tap the battery terminal with the cable you may see a spark. This is caused by the short that is draining your battery. Try removing fuses and disconnecting things until you no longer see the arc. The component that you disconnect and no longer get a spark is what is draining your battery. If it takes more than 24 hours to drain your battery you may not see an arc when you tap your battery cable to the terminal. In that case you will need to use an amp meter to track down the short.

Before we use a multimeter to check current let me take a minute to explain the difference voltage and current. When you read current the electrical current must go through the meter. That is not true when reading voltage. When you use a multimeter to read current you plug the positive meter lead into a different connection on the meter. Set your meter to the highest current setting. Some meters can read up to 20 amps. Either way make sure you have spare fuses for your meter. If you try to read too high of current you will blow the fuse in your meter. Disconnect the negative battery terminal. Put one lead on the battery cable and one on the battery terminal.

Image from agcoauto.com
​

Now unplug fuses and disconnect things until the current drops. This will allow you to see what circuit is drawing current.

 

[BusaDave9]

Good Battery & Starter but engine still won't start

Good Battery & Starter but engine still won't start
If you have an automatic Transmission try starting in park, also try in neutral. The shift lever for an automatic has stops to prevent you from putting it in gear. Push the shift lever against these stops. If this works and the starter runs then the problem is the safety switch that verifies that you are not trying to start the engine in gear. This switch either needs to be replaced or adjusted.

If you have bypassed the starter solenoid as mentioned in the earlier post and the engine started. That tells us that both the starter and the battery are good.
Either the starter solenoid is bad or the ignition switch.

​

Get out your volt meter. Turn the key to run and remove the small red wire (Labeled i in the above pic) from the starter solenoid. Put the red lead from you meter in this connector and the black lead on the negative battery terminal. You should have 12 volts.
Next remove the small blue wire from the solenoid (labeled S in the above pic).

​

Check this voltage when someone turns the key to START. You should have 12 volts. If you do have 12 volts it should have been able to energize the solenoid but your solenoid is bad. Replace it. One other optional test if you don't have a volt meter is to have someone turn the key to run. Then use a wire to bring 12 volts from the battery to the post on the solenoid in the above picture that the small blue wire normally connects to. If this doesn't cause the starter to turn the engine over that verifies the starter solenoid is bad.

Now lets say you do not get 12 volts on the small blue wire when the key is turned to start. The most likely cause is your ignition key switch is bad (the electrical part, not the key part). If you have an automatic Transmission it could also be the Transmission switch that makes sure you are not trying to start it in gear.
If you do not have a voltmeter another way to verify that you have a bad ignition switch is the test mentioned earlier. Have someone turn the key to run. Then use a wire to bring 12 volts from the battery to the post on the solenoid that the small blue wire normally connects to. If this works and turns your starter then you have a bad key switch. It is also possible that you have a bad wire from the key to the solenoid but that is less likely.
If you have an automatic Transmission lets try again starting it in neutral. If that still won't work you need a new ignition switch.

 

[BusaDave9]

Troubleshooting a fuel system

Troubleshooting a fuel system
So your engine won't start and you know it's a fuel problem.
Well, I have to mention the obvious, make sure you have gas in the tank.
If the engine starts fine cold but dies when it gets hot and then won't start again it is very likely that your problem is vapor lock.
Click here to go to the Next Post for Vapor Lock
If you know you have gas in the tank we need to make sure it's getting pumped to the carburetor. Look at where the fuel line goes from the pump to the filter. Remove the line from the filter. Hold the fuel line over a can and have someone try to start the engine.

​

If you get a nice even stream of gas going into the can then the fuel pump and line from the tank are okay. Since we removed the line before the filter that is most likely the cause of the fuel problem. Replace the filter. There is still a chance the problem is the carburetor but that is not as likely as the filter.

If you do not get a good fuel flow into the can you most likely have a bad fuel pump. Before you replace the pump carefully inspect the fuel line from the tank to the pump. If the rubber portion of the fuel line is old and brittle it may have leaks. You may not notice any fuel leaking onto the ground. A small leak may not let gas leak out. Instead the pump may suck air into the leak. (it's easier to suck air than leak fluid) This leak will prevent any fuel from getting to the carburetor.

 

[BusaDave9]

Vapor Lock

Vapor Lock
If your engine starts fine when it's cold but after the engine gets warm or hot the engine dies and won't start then you may have a problem with vapor lock.

To fix vapor lock you first must understand what causes it. Vapor lock is caused when the gas turns to a vapor before it gets to the engine. The underside of a jeep can be very hot. If the fuel line is anywhere near the exhaust it is even more likely to turn to vapor. The stock fuel pump is a mechanical pump installed on the engine block. This type of pump will not be able to suck the fuel if it has turned to a vapor.

The engine compartment is more likely to be hot than the underside of a jeep. If the gas is vaporized as it reaches the carburetor then it will most likely be a frothy foam in the float bowl. A carburetor can't work with that.

Okay, now what do we do to fix vapor lock? Make sure the fuel line is on the opposite side of the frame as the exhaust. If you have dual exhaust that may be unavoidable. You can buy exhaust wrap. This is an insulation that wraps around your exhaust to keep excessive heat from leaving the exhaust system. You can use this same wrap to cover the fuel line. The idea is to keep the heat in the exhaust and the fuel line needs to stay as cool as possible.

Next is the issue of under-the-hood heat. You can ventilate the hood with vents.

The stock fuel pump is a big problem for vapor lock. It sits right on the hot engine and tries to suck the gas from the gas tank. If there is any vapor in the line, the pump will fail since it was not designed to suck a vapor. If the pump does bring the gas to the pump it will only add more heat since it's mounted to the side of the engine. Just about the best cure for vapor lock is to install an electric fuel pump back by the gas tank. The fuel in the tank stays relatively cool. The pump produces low pressure to push the fuel. This pressure helps to keep the fuel in liquid form. An OEM pump that tries to suck the fuel is more likely to end up with a vapor it is unable to suck.

 

[BusaDave9]

Troubleshooting the Ignition System

Troubleshooting the Ignition System
Before we start lets make sure the tune up parts have been replaced recently. The distributor cap, rotor and, if your jeep is pre-1975, points are all tune up parts that should be replaced periodically. If you don't remember when the last time was that these have been replaced then replace them now. As these parts get old they usually don't make the engine stop running one day but instead they cause the engine to run rough. I still recommend replacing them so as not to confuse our troubleshooting.

Your starter cranks the engine but you have determined that you are not getting a spark.
The first thing to check is the voltage on the coil. You can either use a volt meter or a test light. Turn the key to RUN. Put the black lead of the meter (or the ground of the test light) on a good ground such as the negative battery terminal. Put the red lead of the meter on the small red or red and white wire on the coil. The coil should have a + mark.

​

The above picture is of an aftermarket coil. The OEM coil has a connector like this one:

​

With this OEM connector push the red lead of your meter along side the red wire and make sure it contacts the metal contact. You can disconnect this connector to read the voltage.
If you do not have voltage on the + side of the coil when the ignition switch is on then you have a wiring problem.
NOTE: If you have an after market ignition module, such as MSD, it is normal for the wire to the + side of the coil not to have 12 volts. Check out this link: MSD Ignition
Otherwise Click Here to Troubleshoot why the Coil isn't getting 12 Volts
If you do have voltage on the coil then we should go to the next post to check the resistance of the coil.

 

[BusaDave9]

Checking the coil

Checking the coil
To check the resistance of the coil you need to completely disconnect all wires going to it. Set your multimeter to ohms.

Image from ss1car.com
​

The coil is actually a type of transformer. To test the primary put the red lead of the multimeter on the + terminal. Put the black lead on the – terminal of the coil. This should be 1.25 to 1.4 ohms for an OEM coil (other coils will be between 0.4 and 2 ohms)
Then to test the resistance of the secondary move the black multimeter lead to the large center connection. This should be 9K ohms to 12K ohms (9000 ohms to 12,000 ohms) for an OEM coil or 6K ohms to 15K ohms for other coils.
If the resistance is not within these specs replace the coil.
If the coil is within specs Click here to check the Spark Plug Wireshttp://www.jeep-cj.com/forums/f97/e...leshooting-guide-19429/index2.html#post158743

 

[BusaDave9]

Spark Plug Wires

Spark Plug Wires
At this point we need to make sure the spark plug wires are good. Normally when a spark plug wire goes bad the engine will start. It just wouldn't run smoothly. For that reason the most important wire we need to check is the wire from the coil to the distributor. This one wire carries the spark for all the cylinders. When it fails the engine will not start. Remove this wire and check its resistance. The resistance of this wire and the spark plug wires, depend on the length. The resistance of the short wire that goes from the coil to the distributor should be between 3000 ohms to 10,000 ohms. The longer spark plug wires should be between 4000 and 15,000 ohms. Performance wires may have lower resistance. This may sound confusing but just compare the wires to each other and keep in mind that the longer wires will have higher resistance. When these wires go bad, it's usually a break in the conductor and the resistance jumps to infinity. The meter may act like you are not even touching the leads to the wire ends.
If the resistance is too high replace the wires.
If the spark plugs are good we need to check the distributor.

Click here if your jeep was built before 1975 to check the Distributor

Click here to check the distributor of an Electronic Ignition (post 1975)

 

[BusaDave9]

Checking a Points Distributor

Checking a Points Distributor
If your jeep was made before 1975 you have points in the distributor to time the spark. This is a very simple system. The points act like a switch that opens and closes as the distributor rotates. This sends pulses to the coil to produce the spark that is sent back to the distributor and then on to the spark plugs. The points and condenser are tune up parts that should be replaced periodically. If the distributor is not producing a spark replace the points and condenser and adjust the dwell.
I highly recommend replacing old points distributors with newer technology distributors. One option is to get a distributor from a post '75 jeep with electronic ignition. Then do the Team Rush upgrade. Click here for the thread on Team Rush upgrade. Another option is to install an HEI ignition. This is a very simple upgrade with only one wire needed to power the distributor. If you are having trouble with your engine starting I don't like doing an upgrade at the same time as a repair. Make sure the distributor is the problem before you decide to replace it.

 

[BusaDave9]

Checking an Electronic Ignition Distributor

Checking an Electronic Ignition Distributor
Let me say right now, it is rare to need to replace the entire distributor. Usually it is only a compartment of the distributor that goes bad.
The wear items on the distributor are the distributor cap and rotor. Sometimes an electrode will break off but for the most part when a distributor cap or rotor goes bad usually the engine just runs rough.
If the tune up parts are okay the most likely part in an electronic ignition distributor to go bad is the pickup assembly but this is still not a common point of failure. The purpose of the pickup assembly is to decide when the spark should be created.

I have tried to keep this thread generic. This troubleshooting should apply to all Jeep CJ engines (and may other older engines). But now we are deep into the ignition system. These pickup assemblies are specific to the engine and make. The AMC pickup assemblies are similar. If the troubleshooting brought you to this post please start a new thread to ask and make sure you are on the right track.

The 3 prong connector going into the base of the distributor is the pickup assembly. Disconnect this. Set your meter to ohms. Put the 2 leads into the 2 opposite pins on the connector going into the distributor. This should read 400 ohms to 800 ohms for an AutoLite ignition on a 4, 6 or 8 cylinder AMC engine.

 

[BusaDave9]

Coil Not Getting 12 Volts

Coil Not Getting 12 Volts

When we are not getting a spark the first voltage to check is the small wire on the coil marked with a plus sign. This should be 12 volts whenever the key is turned to RUN. If not the problem is most likely the ignition key switch but before we jump to conclusions we need to take a step back and review our troubleshooting to make sure we are on the right track.
If the starter can crank the engine over we know the battery is good (it takes a lot more current to power the starter than the ignition). Does the radio and other accessories work? Does the lights work. The headlights do not get their power through the ignition switch. So if the headlights work but you don't have 12 volts on the coil then check to see if you have a ballast resistor. Older CJs would have a ballast resistor from the factory but if a PO replaced the coil the ballast resistor may have been removed. Trace the small wire back from the + side of the coil. A ballast resistor is a large power resistor that would look something like this:

Check the voltage on both ends of the ballast resistor when the key is turned to RUN. If you get 12 volts on one end but not on the end of the resistor that is connected to the coil then replace the resistor. These ballast resistors are able to handle a lot of power so they rarely go bad. To double-check a ballast resistor check its resistance with a multimeter. It should have less than 2 ohms.

If you ar not getting voltage on the coil or ballast resistor you will need a new ignition switch.

 

[BusaDave9]

This was meant as a general troubleshooting guide. If you followed this thread and are still having trouble please start a new thread and let us know what troubleshooting you have done.