How To Test The Fuel Injectors (4.2L Ford F150, E150, E250)

How To Find The Bad Or Clogged Fuel Injector

What complicates testing the fuel injectors on the 4.2L Ford engines is the fact they're not easily accessible. Not only that but in the majority of cases, in which we suspect a fuel injector is causing the misfire, it's really an ignition system component behind it.

Keeping this in mind, my diagnostic strategy has always been to eliminate a few variables before attempting to test the fuel injectors (in order to avoid removing the upper intake manifold in vain).

In my opinion (and professional experience), the most important thing is to first find the 'dead' cylinder and then eliminate the ignition system as the source of the problem.

1. Find the 'dead' cylinder first.
   • This requires checking for specific misfire codes (P0301, P0302, P0303, P0304, P0305, P0306) or doing a cylinder balance test.
2. Once the 'dead' cylinder has been identified, the next step is to make sure it's getting spark.
   • You must use a dedicated spark tester to check for spark.
   • It's important that you check that the spark plug boot and spark plug wire are not damaged, cut, or burned.
   • You should also remove the spark plug and check it for cracks or carbon tracks (this is SO important).
     • Here's a real life case study on carbon tracks and how they can cause a misfire: Carbon Tracks Are A Common Cause Of Ignition Misfires.
   • The key here is to eliminate the ignition coil, the spark plug wire and the spark plug as the cause of the cylinder's misfire.
     • The following tutorial will show you how to test the spark plug wires and the ignition coil: How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L).
3. If spark is present, then the next step is checking that that cylinder has good compression.
   • This is one of the most overlooked tests when diagnosing a misfire or rough idle condition. You can find the test here:
     • How To Do An Engine Compression Test (4.2L Ford V6).
4. Noid light test.
   • If every test above checks out OK, then the next step is to do a fuel injector Noid light test.
   • The Noid light test will help you make sure that the fuel injector is being activated.
   • The following Noid light article/tutorial may help you: How To Use A Noid Light And Where To Buy It (I know that this is not the most in-depth article on the subject, but it should give you an idea of what is involved).
5. Swap the fuel injector with its neighbor on the fuel injector rail.
   • I'll swap out that fuel injector with its neighbor if:
     1. The ignition system is not at fault.
     2. That cylinder's compression value is good (compared to the rest of the cylinders).
     3. The fuel injector resistance is good.
     4. I think the fuel injector is clogged.
     If the misfire now follows that swap, I now know that fuel injector is clogged (or bad) and needs to be cleaned or replaced.

The most important thing to remember is to first identify the misfiring cylinder. Once you've identified it, keep in mind that either air, spark or fuel is missing and keeping that cylinder from producing power.

Precautions To Take When Removing The Intake Manifold Plenum

Before you remove the intake manifold's plenum, keep in mind several important things:

1. Buy or borrow a repair manual (preferably a Haynes Repair Manual -Chilton manuals suck) so that you can have the intake manifold removal process explained in detail.
   • The manual will also give you the torque specifications for the bolts.
2. Be careful that no foreign object, like a bolt, a nut, or any metal piece/part, falls into the open manifold port runners.
3. Once the plenum has been removed, place a clean rag or rags on the open intake runners. This will keep things from falling into them.
4. As you're removing bolts, nuts and stuff from the intake plenum to remove it, place them in a container and away from the engine compartment.

Anything falls into the open intake runners, without you knowing, and the engine is started, you are going to be in a big world of hurt! Since it may require the removal of the cylinder head to retrieve the part that fell in. So be alert and be careful.

Removing the plenum is not an out of this world thing that no one can do, it's done around the country in many shops without complications or unhappy endings by simply following some precautions.

More 4.2L Ford Diagnostic Tutorials

You can find a complete list of 4.2L Ford tutorials in this index:

• Ford 4.2L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test Engine Compression (4.2L Ford).
• How To Test The Throttle Position Sensor (4.2L Ford F150, E150, E250).
• How To Test The Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor.
• How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L).