How To Troubleshoot A No-Start Problem (4.0L Ford Explorer, Aerostar, And Mercury Mountaineer)

Testing a cranks but does not start condition on your 4.0L Ford Explorer (Aerostar, Mercury Mountaineer) doesn't have to be complicated.

In this tutorial, I'll go into the basics of a no-start condition and show you some of the step-by-step tutorials that'll help you get to the bottom of the problem.

NOTE: You can find the 4.0L Ford Ranger and Mazda B4000 no-start tutorial here:

• How To Diagnose A No-Start Problem (4.0L Ford Ranger And Mazda B4000) (at: easyautodiagnostics.com).

You can find this tutorial in Spanish here: Cómo Probar Un Arranca Pero No Prende (4.0L Ford) (at: autotecnico-online.com).

Difference Between A No-Crank And A No-Start Condition

There's a big difference between a no-crank and a no-start condition. Here's a brief description of both conditions:

No-Start Condition: The engine cranks (turns over) like it wants to start, but it never does. The usual culprits are:

• A bad crank position sensor.
• A bad fuel pump.

No-Crank Condition: The engine does not turn over when you turn the key to start your Ford vehicle. This is usually due to:

• A bad starter motor.
• A bad neutral safety switch.
• A bad ignition switch.
• The engine is locked up.

This tutorial is geared toward a cranks but does not start condition. So if you've got a no-crank problem, start with testing the starter motor.

The following tutorial will help you test the starter motor:

• How To Test The Starter Motor (4.0L Ford Explorer, Aerostar, And Mercury Mountaineer).

No-Start Condition Basics

To successfully troubleshoot the cause of the no-start condition of your Ford 4.0L Explorer (Aerostar, Mercury Mountaineer), you need to know that there are three fundamental components the engine needs to start, and they are:

1. Air.
2. Fuel.
3. Spark.

So, when your Ford 4.0L Explorer (Aerostar or Mercury Mountaineer) cranks but does not start, it's because one of these components is missing from the mix.

This simple but essential information lets you know that the engine no-start problem will lie in the fuel system, ignition, or the engine.

Here are some more specifics:

1.)  Ignition System

• The ignition system is the one responsible for creating and delivering spark. Without spark, the engine will crank but not start.
• The ignition system of the Ford 4.0L equipped vehicles covered by this article use a distributor-less ignition system. More specifically, it uses a coil pack type ignition system.
• In my experience, the most common component failures of the ignition system that causes a no-start no-spark condition are:
  • The ignition coil pack is not receiving power.
  • A bad crankshaft position sensor.
• You can systematically test the ignition system components to precisely determine what has failed (if indeed something has).

2.)  Fuel System

• The fuel system is the one responsible for supplying the engine with fuel.
• The fuel system component that causes the majority of no-start no-fuel problems:
  • A bad fuel pump relay.
  • A bad fuel pump.
  • The fuel pump inertia switch (tripped and cutting power to the fuel pump).
• You can easily test the fuel pump (along with the other two components) to make sure it has fried.

3.)  Engine (Mechanical System)

• The engine pistons and cylinder head valves (and all the other related components like timing chains, etc.) are responsible for the induction of the fresh air the engine needs for the combustion process.
• Although rare, internal engine mechanical problems can and do cause no-start conditions.
• Possible internal engine problems are:
  • A blown head gasket.
  • A blown engine.
  • A broken timing chain (although this is very rare).

OK, the list of possible things that can go wrong looks pretty long, but it is rare to see (or have) two different components go bad from two separate systems simultaneously.

The cool thing is that there is a diagnostic strategy that you can use to figure out precisely what's wrong with your particular no-start problem. Let's find out more about it in the following sections.

STEP 1: Checking For Spark

Testing the ignition system is usually the easiest of all the tests done to find the cause of the cranks but does not start condition.

Usually, most of the 'cranks but does not start' conditions I've troubleshot and repaired over the years had their root cause in the ignition system.

So, my recommendation is to check for spark at all of the spark plug wires with a spark tester.

Testing the ignition system on your Ford 4.0L Explorer (Aerostar or Mercury Mountaineer) isn't difficult. I've written a tutorial that'll show you in a step-by-step manner, and you can find it here:

• How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L) (at: easyautodiagnostics.com).

The ignition system is NOT causing the no-start problem if:

• Spark is present at all 6 spark plug wires.

With all 6 spark plug wires delivering spark to the cylinders (spark plugs), you can conclude that the ignition system is NOT causing the engine no-start problem.

You can also conclude that:

• The crankshaft position (CKP) sensor is good.
• The ignition control module (ICM) is good (if equipped).
• The ignition coil pack is good.

Since the ignition system is creating and feeding spark to the engine cylinders, the next test steps are to test the fuel pump's pressure. Go to: STEP 2: Checking For Fue.

The ignition system IS THE CAUSE of the no-start problem if:

• You got NO spark at all 6 spark plug wires.

The components that can cause this no-spark problem are:

• A bad crankshaft position (CKP) sensor.
• A bad ignition control module (ICM) -if equipped.
• In some rare cases, a bad ignition coil pack.

Your next steps are to:

• Test the crankshaft position (CKP) sensor.
  • How To Test The CKP Sensor (1991-1997 4.0L Ford Explorer And Aerostar).
  • How To Test The CKP Sensor (1997-2010 4.0L Ford Explorer And Mercury Mountaineer).
• Test the ignition control module (ICM) -if equipped.