How To Test The Fuel Injectors (1997-2000 4.2L V6 Ford F150, F250)

Testing the fuel injectors on the 1997-2000 Ford 4.2L V6 F150 and F250 isn't for the faint of heart. What complicates testing them is the fact that they're located underneath the intake manifold plenum, and this bad boy has to be removed to access them.

If that weren't enough, in the majority of cases, in which a fuel injector is suspected of causing a cylinder misfire, it's really an ignition system component or a low cylinder compression issue that's at fault.

In this tutorial, I'm gonna share with you my way of diagnosing them —a process I've honed over the years— that has helped me find out if a fuel injector is bad or clogged. I think this diagnostic strategy will help you eliminate a few variables before testing the fuel injectors (in order to avoid removing the upper intake manifold unnecessarily).

APPLIES TO: This tutorial applies to the following vehicles:

• 4.2L V6 Ford F150: 1997, 1998, 1999, 2000.
• 4.2L V6 Ford F250: 1998.

2001-2003 Fuel Injector Tests: The fuel injector tests for the 2001-2003 4.2L Ford F150 can be found here:

• How To Test The Fuel Injectors (2001-2003 4.2L V6 Ford F150).

Wiring Diagrams: The following fuel injector circuit wiring diagrams are available:

• Fuel Injector Circuit Wiring Diagram (1997-1998 4.2L V6 Ford F150, F250 Light Duty).
• Fuel Injector Circuit Wiring Diagram (1999 4.2L V6 Ford F150).

E-SERIES VANS: The fuel injector troubleshooting tutorial for the 1997-2000 4.2L V6 Ford E150/E250 vans can be found here:

• How To Test The Fuel Injectors (1997-2000 4.2L V6 Ford E150, E250) (at: troubleshootmyvehicle.com).

Symptoms Of A Bad Fuel Injector

Fuel injectors tend to suffer from one of two complications:

• Internal short circuit or open circuit problem: In this scenario, the internal winding of the fuel injector has an electrical problem, causing the injector to stop injecting fuel.
• Clogged fuel injector: When this happens, the fuel injector can inject fuel, but it doesn't atomize it correctly. In other words, it doesn't spray the fuel in a fine mist. Since it can't atomize the fuel correctly, the cylinder will misfire because the non-atomized fuel cannot combust properly.

Whether the fuel injector suffers from an internal electrical problem or gets clogged, the end result is the same: the cylinder that the fuel injector supplies fuel to will misfire.

Here are some more specific symptoms when a fuel injector fails or gets clogged:

• Rough idle.
• Lack of power.
• Hesitation when you accelerate your 4.2L Ford pickup down the road.
• Since the 4.2L Ford pickup is OBD II equipped, you'll see a misfire diagnostic trouble code (DTC):
  • P0300: Random Cylinder Misfire.
  • P0301: Cylinder #1 Misfire.
  • P0302: Cylinder #2 Misfire.
  • P0303: Cylinder #3 Misfire.
  • P0304: Cylinder #4 Misfire.
  • P0305: Cylinder #5 Misfire.
  • P0306: Cylinder #6 Misfire.

Whether the fuel injector is fried internally or clogged, this tutorial will offer you some specific suggestions to help you narrow down the possible solution.

What Tools Do I Need To Test The Fuel Injectors?

To perform a fuel injector resistance test, you don't need a lot of stuff. Here's a basic list of tools you'll need:

1. A multimeter.
   • The multimeter will help you check the internal resistance (Ohms) of the fuel injector(s).
   • If you need to upgrade or buy a multimeter, check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing.
2. Hand-held DIY fuel injector cleaning tool kit.
   • This tool allows you to pulse (activate) the fuel injector while connected to a spray can of brake cleaner, making it super easy to visually check the injector's spray pattern and see if it's clogged.
   • You can learn more about this tool and where to buy it in this section: PART 2: Checking The Fuel Injector Spray Pattern.
3. A fuel injector pigtail connector.
   • The pigtail connector comes in handy when testing the resistance of the injectors with the intake manifold plenum installed.
4. OBD II scan tool or code reader.
   • To actually test the fuel injectors, you don't need a scan tool (since a scan tool can't dynamically test the fuel injectors). But, having one makes the whole process easier since you're able to retrieve any diagnostic trouble codes (DTCs) stored in the PCM memory.
5. Hand Tools.
   • Since half of the fuel injectors are underneath the intake manifold plenum, you'll need hand tools like: socket wrench, extensions, sockets, etc. to remove it.
6. Pen and Paper to write down your fuel injector resistance test results.

Start Here: Diagnostic Strategy

The one thing that complicates testing the fuel injectors on your Ford F150/F250 pickup with a 4.2L V6 engine is that they're located underneath the aluminum intake manifold plenum. I'll be honest, it has to be removed to access and test them.

It's important to keep in mind that fuel injector failures are not very common. What I'm trying to say is that other issues could cause a cylinder misfire and make you think it's a bad or clogged fuel injector.

To avoid the frustration of removing the intake manifold plenum when you don't have to, I'm gonna outline the testing roadmap I use to find out if a fuel injector is bad or clogged and causing a cylinder misfire:

1. First, identify the 'dead' cylinder.
   • Knowing which cylinder is the 'dead' is the most critical part of the diagnostic process. This will save you a lot of troubleshooting time and help you avoid the frustration of replacing parts that won't fix the issue (since quite a few things besides a bad or clogged injector can cause a cylinder to misfire).
   • Usually, a cylinder misfire diagnostic trouble code (DTC) will help identify the 'dead' cylinder, but not always. If there's no specific DTC, you might need to perform a manual cylinder balance test.
   • Once you've located the 'dead' cylinder, the next step is to rule out the ignition system as the cause of the misfire.
2. Test the ignition system and make sure it's delivering spark to the 'dead' cylinder.
   • To check for spark, you'll need to:
     1. Use a spark tester on the spark plug wire to check for spark.
     2. Inspect the spark plug wire for any damage or excessive wear and tear.
     3. Remove and inspect the spark plug for any signs of damage.
   • The ignition system (whether it's the coil pack, spark plug wire, or the spark plug) is responsible for 90% of misfires, so it's best to eliminate it as a cause from the start.
   • You can find the ignition system tests here: How To Test The Ignition Coils (1997-2000 4.2L V6 Ford E150, E250) (at: troubleshootmyvehicle.com).
   • If the cylinder is getting spark, the spark plug wire is OK, and the spark plug doesn't show any signs of damage, the next step would be to test that cylinder's compression. If you find that the cylinder isn't getting spark, then you've found the issue causing the cylinder misfire.
3. Compression test the 'dead' cylinder.
   • You don't have to test all 6 cylinders, just testing the 'dead' cylinder plus two others (to compare your compression test results to) is enough to get an idea of the internal health of that cylinder.
   • You can find the test explained here: How To Test Engine Compression (1997-2006 4.2L V6 Ford F150, F250).
   • If the 'dead' cylinder has good compression, the next step is to test the fuel injector's resistance. If it doesn't have compression, then you've found the cause of the cylinder misfire issue.
4. Test the fuel injector.
   • The first thing is to test the internal resistance of the fuel injector of the 'dead' cylinder.
   • The second part of the test involves using brake cleaner spray with a special adapter tool to visually check whether the fuel injector is indeed spraying fuel.

I've used the above diagnostic strategy with a ton of success and I think it'll help you too.

Where To Buy The Fuel Injector And Save

The following links will help you comparison shop for the fuel injector on your 4.2L V6 Ford pickup:

1997-1998 4.2L V6 F150 and F250:

1999-2000 4.2L V6 F150 and F250:

Not sure if the above fuel injectors fit your particular 4.2L Ford pickup? Don't worry, once you click on the links and arrive on the site, they'll make sure it fits! If it doesn't, they'll find you the right one.

PART 1: Checking The Injector's Internal Resistance

Alright, as you know, removing the upper intake manifold plenum is necessary to access the fuel injectors. Although I don't provide detailed remove and replace (R&R) instructions, I do have some tips for you before you begin. You can check them out here:

• Precautions To Take When Removing The Intake Manifold Plenum.

Another thing I want to point out: Testing the resistance of some of the fuel injectors can be a bit of a challenge because of their location on the engine (yeah, even with the plenum removed). It can be tricky to probe the male spade terminals of the fuel injector with the multimeter test leads (to get their resistance reading).

I've found that the best way to go about it is to use a fuel injector pigtail connector, which I buy online. I connect the pigtail to the fuel injector and then measure the resistance by probing the connector's exposed wire ends.

By using the fuel injector pigtail connector, I get an accurate resistance measurement and also avoid the difficulty of accessing the injectors' male spade terminals directly (with the test leads).

NOTE: Don't have a multimeter or need to upgrade yours? Check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing.

Alright, here are the steps:

1. 1

   Remove the intake manifold plenum.

2. 2

   Disconnect the fuel injector from its electrical connector.
   
   NOTE: The illustration above will help you identify the cylinder the fuel injector belongs to.

3. 3

   Place your multimeter in Ohms (Ω) mode.

4. 4

   Measure the resistance of the fuel injector across its two male spade terminals with the multimeter test leads (see the illustration above).
   
   You should see a resistance value between 11 to 18 Ohms (with the engine completely cold).
   
   Measure the resistance of the same fuel injectors several times so that you can be sure of your multimeter's Ohms result.

5. 5

   Write down the resistance value that your multimeter records for the specific fuel injector you're testing.

6. 6

   Repeat steps 2 through 5 on any other fuel injector you need to test.

Let's find out what your specific multimeter test results mean:

CASE 1: The resistance of the 'dead' cylinder's fuel injector is within specification. This tells you that this particular fuel injector doesn't have an internal short or open-circuit problem.

Your next step is to check that the fuel injector isn't clogged. Go to: PART 2: Checking The Fuel Injector Spray Pattern.

CASE 2: The resistance of the 'dead' cylinder's fuel injector IS NOT within specification. This tells you that the fuel injector is bad. Replace the fuel injector.