STEP 2: Checking For Fuel
Fuel pumps fail all of the time, and if the fuel pump has failed in your 4.0L Ford Explorer (Aerostar or Mountaineer), you'll have a bonafide 'cranks but does not start' condition on your hands.
But, before testing the fuel pump, you should make sure that the fuel pump inertia switch hasn't shut down the fuel pump. Checking the fuel pump inertia switch simply involves pressing down on its re-set button to see if it clicks.
If the fuel pump inertia switch clicks, as you're pressing down on its re-set button, then the fuel pump should start working again, and the engine should start.
Suppose the fuel pump inertia switch is OK. In that case, the next step is checking to see if the fuel pump is producing the correct fuel pressure. The absolute best way to do it is with a fuel pressure gauge.
You can find the fuel pump pressure test explained here:
The fuel system is NOT causing the no-start problem if:
- Fuel pressure is within specification.
If the fuel pressure gauge registers the indicated fuel pressure specification, then you can confidently conclude that the fuel pump is working and delivering enough fuel to the fuel injectors.
You can also conclude that the fuel pump is not behind the engine's no-start problem.
The next step is to check for a blown head gasket. Go to: STEP 3: Checking For A Blown Head Gasket.
The fuel system IS THE CAUSE of the no-start problem if:
- Fuel pressure is 0 PSI (or anything below the fuel pressure specification).
This confirms that the no-start problem is caused by a lack of fuel. This usually means that the fuel pump is bad and needs to be replaced.
STEP 3: Checking For A Blown Head Gasket
A head gasket failure is usually the result of an engine overheating issue.
The 4.0L V6 engine in your Ford Explorer (Aerostar or Mercury Mountaineer) comes equipped with two cylinder head gaskets.
There are 4 specific tests to check for a blown head gasket, and you can find them explained in this tutorial:
A blown head gasket is NOT causing the no-start problem if:
- The engine oil has a normal color (in other words, it doesn't have a milky-white color).
- The coolant in the radiator remains undisturbed when cranking the engine (with the radiator open).
- The engine passed a block test.
Your next test is to check the engine's compression. Go to: STEP 4: Making Sure The Engine Has Good Compression.
A blown head gasket IS THE CAUSE of the no-start problem if:
- The engine oil has a milky-white color (like coffee with too much creamer).
- - or -
- The coolant in the radiator shot out when cranking the engine (with the radiator open).
- - or -
- The engine failed a block test.
STEP 4: Checking Engine Mechanical Condition
The engine in your vehicle could have an internal mechanical problem and be the source of the 'cranks but does not start' condition.
The way to find out if the engine is the cause of the no-start is to do a compression test.
When performing an engine compression test, what you're looking for is an average compression reading of NO LESS THAN 90 PSI across all or the majority of the engine cylinders.
I've written an engine compression test tutorial that you may find useful. You can find it here:
An engine compression problem is NOT causing the no-start problem if:
- The compression of each cylinder is above 120 PSI.
An engine compression problem IS THE CAUSE of the no-start problem if:
- 2 or more cylinders have 0 PSI compression.
- - or -
- All cylinders have 0 PSI compression.
No Start Summary
When troubleshooting a 'cranks but does not start' condition, the key to saving yourself time, money, and a lot of frustration is to check the basics first. The basics are spark, fuel, and air (engine cylinder compression).
To check the basics, you need tools. There's just no way around it. One of the analogies that I've always enjoyed repeating about doing a job without the right tools is like trying to eat a bowl of soup with a fork.
So besides knowing what to test, you need tools to do those tests. You don't have to spend an arm and a leg since you can buy a lot of these diagnostics tools inexpensively online.
Here are some of the essential tools you'll need:
- A fuel pressure gauge.
- A spark tester.
- A compression gauge.
- A multimeter.
More 4.0L Ford Explorer, Aerostar, And Mercury Mountaineer Tutorials
You can find more 4.0L V6 Ford Explorer diagnostic tutorials here:
Here's a sample of the tutorials you'll find in the index:
- How To Test For A Blown Head Gasket (Ford 4.0L Explorer, Aerostar And Mercury Mountaineer).
- How To Test The Fuel Pump (Ford 4.0L Explorer, Aerostar And Mercury Mountaineer).
- How To Test Engine Compression (1991-2010 4.0L Ford Explorer, Aerostar, And Mercury Mountaineer).
If this info saved the day, buy me a beer!