No Start 1: Checking For Spark
Before replacing anything, the first thing you should do is check what system is missing what. The first order of business should be testing for spark and fuel.
To be a bit more specific, you should:
- Make sure all 6 (3.9L V6) or all 8 cylinders are getting spark with a spark tester.
- If spark was present in all of the cylinders, then this result tells you several very important things:
- The distributor cap, distributor rotor, and the spark plug wires are OK.
- The ignition coil is OK and functioning correctly.
- The crankshaft (crank) position sensor is functioning correctly.
- The Auto Shut Down (ASD) relay, which powers the ignition coil, is good.
- If after checking for spark and there IS NO spark present in all 6 or 8 cylinders, then the most likely causes are:
- Bad ignition coil high tension wire (this is the spark plug wire that connects the ignition coil to the distributor cap).
- Bad distributor cap and/or rotor.
- Bad ignition coil.
- Bad crankshaft position sensor.
NOTE: One of the most common failures on these Dodge vehicles is a bad crank sensor causing a no-start condition. Since the crank sensor is at the heart of everything that is involved with starting the vehicle. When the crank sensor has failed you'll see the following specific symptoms:
- The PCM will not activate the fuel injectors.
- The PCM will not activate the ASD (Auto Shut Down relay).
- If the ASD relay does not activate, the ignition coil will not get power.
- If the ASD relay does not activate, the fuel pump relay will not activate.
The crank sensor can be accurately test with just a multimeter:
- How To Test The Crank Sensor (1994-1996 3.9L, 5.2L, 5.9L Chrysler).
- How To Test The Crank Sensor (1997-2001 3.9L, 5.2L, 5.9L Chrysler).
You can find the ignition coil and ignition control module test here:
No Start 2: Checking For Fuel
If the fuel does not reach the fuel injectors or if the injectors do not spray the fuel into the engine cylinders, for whatever reason, you'll get a ‘no fuel no-start condition’.
The usual suspect behind a ‘lack of fuel keeping the engine from starting’ is the fuel pump. Either because the fuel pump has failed completely and isn't sending any fuel to the fuel injectors or because it's not sending enough.
To get an accurate fuel pump diagnostic test result, you should test the fuel pump with a fuel pressure gauge (any other method may have you wasting time and money on a fuel pump your vehicle does not need).
The following tutorial explains how to test the fuel pump on the V8 Dodge Ram pickups:
When checking fuel pump pressure, keep the following in mind:
- If the fuel pump pressure (as checked with a fuel pressure gauge) is OK, then this tells you:
- Fuel pump is OK.
- Fuel pump fuse is OK.
- Fuel pump relay is OK.
- If the fuel pressure is not at specification (or it's 0 PSI), then the most likely cause is:
- A bad fuel pump but not always (there are no absolute truths in life but death and taxes).
If the fuel pressure gauge indicates 0 PSI pressure, I would recommend testing/checking the following before condemning the fuel pump:
- After verifying that no fuel pressure exists, check that the fuel pump is getting power (12 Volts).
- This can be done by tapping into the power circuit that feeds the pump with 12 Volts with a multimeter (but without dropping the fuel tank to remove the fuel pump).
- Once you're tapped in, have a helper crank the engine while you observe your multimeter in Volts DC mode. If voltage is present (12 Volts), then you have confirmed that the fuel pump fuse and fuel pump relay are working perfectly.
- If your multimeter registers 12 Volts, you can replace the fuel pump with confidence.
- If no voltage is present, as your helper cranks the engine, then the fuel pump should not be replaced. You need to find the cause of this missing voltage.
If after checking and confirming that your Dodge's engine is getting spark and fuel, the next step is to check the engine's mechanical condition with a compression test. Let's turn the page and find out more.