In this tutorial, I'm gonna show you a very effective fuel injector diagnostic strategy that'll help you identify which fuel injector is bad/clogged and causing an engine cylinder misfire.
The cool thing is that you won't be needing any expensive diagnostic equipment to do this and with your test results, you'll quickly identify which fuel injector is the one causing the engine performance issue.
Contents of this tutorial:
- The Two Main Types Of Fuel Injector Failures.
- Symptoms Of A Bad Or Clogged Fuel Injector.
- What Tools Do I Need To Test The Fuel Injectors?
- Start Here: Diagnostic Strategy.
- PART 1: The Fuel Injector Resistance Test.
- PART 2: Checking The Fuel Injector Spray Pattern.
- Important Tips For Installing A Fuel Injector.
- More 4.6L Ford E150, E250, And E350 Test Tutorials.
APPLIES TO: Applies to the following gasoline powered vehicles:
- 4.6L, 5.4L Ford E150: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.
- 4.6L, 5.4L Ford E250: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.
- 5.4L Ford E350: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.
F-Series Pickups: You can find the fuel injector test for 4.6L and 5.4L V8 F-Series pickups here:
- How To Test The Fuel Injectors (1997-2002 4.6L Ford F150, F250, F350) (at: easyautodiagnostics.com).
Crown Victoria And Grand Marquis: You can find the fuel injector tests for 4.6L Crown Vic/Grand Marquis here:
- How To Test The Fuel Injectors (1992-1997 4.6L Crown Victoria, Grand Marquis).
- How To Test The Fuel Injectors (1998 4.6L Crown Victoria, Grand Marquis).
- How To Test The Fuel Injectors (1999-2000 4.6L Crown Victoria, Grand Marquis).
NOTE: This tutorial applies to several other Ford, Mercury, and Lincoln vehicles equipped with a 4.6L or 5.4L V8 engine. You can see the application list in the 'Applies To' box on the left if you're using a desktop or at the bottom of this page if you're using a hand-held mobile device.
The Two Main Types Of Fuel Injector Failures
For the most part, fuel injectors will suffer one of the two following types of failures:
- The fuel injector suffers an internal electrical problem: In this type of failure, the fuel injector's internal windings suffer from an electrical open or short-circuit problem. This internal issue will keep the fuel injector from spraying any fuel.
- The fuel injector becomes clogged: The fuel injector becomes clogged and is unable to spray fuel in a fine mist.
Whether the fuel injector suffers an internal electrical problem or gets clogged, the end result of both of these issues is that the engine cylinder that the fuel injector sprays fuel into will simply misfire.
I would like to add that in the case of a clogged fuel injector, even though it's still spraying fuel, it usually sprays it in a squirt or stream instead of a fine mist. The ability of the fuel injector to atomize (spray in a fine mist) is critical for complete fuel combustion within the cylinder. When the fuel injector can't do that, its engine cylinder will under-perform.
Knowing that the majority of fuel injector failures fall within these two categories is winning half the battle.
Symptoms Of A Bad Or Clogged Fuel Injector
As mentioned before, the main symptom of a bad/clogged fuel injector is an engine cylinder misfire, but it's not the only one. You might notice some other symptoms, including, but not limited to:
- Lack of power.
- Bad gas mileage.
- Check engine light (CEL) is on.
Now, to go into more specifics of how a fuel injector can fail:
- The fuel injector suffers an internal electrical failure and won't spray any fuel.
- The fuel injector gets clogged and won't spray enough fuel or in the proper spray pattern.
- The fuel injector doesn't activate (spray) because it's not getting power.
- The fuel injector doesn't activate because the fuel injection computer doesn't activate it (although it may be getting power).
- PCM goes bad and activates the fuel injector as soon as the key is turned to the RUN position.
No matter what the root cause, a bad fuel injector will cause the engine to idle rough and miss when you accelerate the van down the road.
What Tools Do I Need To Test The Fuel Injectors?
To follow this tutorial and perform a fuel injector resistance test and spray test, you'll need the tools in the following list:
- 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 (found at: easyautodiagnostics.com).
- 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.
- A fuel injector pigtail connector.
- The pigtail connector comes in handy when testing the resistance of the injectors in hard to reach/access areas.
- 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.
- 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.
- Pen and Paper to write down your fuel injector resistance test results.
Start Here: Diagnostic Strategy
A solid diagnostic strategy is the key to saving time and money by avoiding replacing unnecessary parts. This strategy involves performing a few tests to eliminate a few other components that can cause an engine cylinder misfire (like low cylinder compression, a bad ignition coil, etc).
The following troubleshooting 'road map' is the one I use, and I'm certain it'll help you pin-point the exact cause of the cylinder misfire issue, whether it's caused by a bad/clogged fuel injector or something else:
- First, identify which cylinder is the 'dead' one.
- This first step is crucial because it'll significantly reduce the time you'll spend troubleshooting the problem and it helps you avoid the frustration of replacing parts that won't fix the issue. A misfiring cylinder can be caused by numerous factors, not just a bad or clogged injector.
- In many instances, a diagnostic trouble code (DTC) for a cylinder misfire will clearly indicate the 'dead' cylinder -but not always. If there's no DTC specifying a particular cylinder, you might need to do a manual cylinder balance test.
- Once you've pinpointed the 'dead' cylinder, the next step is to rule out the ignition system as the cause of the misfire.
- Make sure the ignition system is delivering spark to the 'dead' cylinder.
- This involves confirming that the 'dead' cylinder is receiving spark. This is how you can do that:
- Use a spark tester to check each ignition coil (COP coil equipped) or spark plug wire (ignition coil pack equipped) for spark.
- Check the spark plug boot for any visible signs of wear or damage.
- Remove and examine the spark plug for any damage.
- The ignition system is frequently the source of about 90% of misfires and it's important to make sure its creating and delivering spark to the 'dead' cylinder early in your troubleshooting process.
- The following tutorials will help you:
- If the cylinder is getting spark, the spark plug wire or COP coil boot is intact, and the spark plug shows no signs of damage, the next step is to test that cylinder's compression. Now, if there's no spark, you've pinpointed the cause of the misfire.
- This involves confirming that the 'dead' cylinder is receiving spark. This is how you can do that:
- Do a compression test on the 'dead' cylinder.
- You don't need to test all eight cylinders. If you test the 'dead' one plus two others (for comparison), you'll have enough info to conclude if the 'dead' cylinder has an internal mechanical problem.
- You can find the compression test explained here: How To Test Engine Compression (1997-2007 4.6L, 5.4L V8 Ford E150, E250, E350).
- If the 'dead' cylinder exhibits good compression, the next action is to measure the resistance of the fuel injector. On the other hand, if the cylinder lacks adequate compression, you have likely identified the root cause of the misfire issue.
- 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.
PART 1: The Fuel Injector Resistance Test
After identifying the 'dead' cylinder and confirming it's getting spark and has good compression, the next step is testing the resistance of its fuel injector.
Some of the fuel injectors, because of their locations, can be a bit difficult to directly probe their male spade terminals with multimeter test leads.
On those particular fuel injectors, a helpful technique I've used is to use a fuel injector pigtail connector (which I purchased online) to test their resistance.
This is how it works: I connect the pigtail connector to the fuel injector. I then probe the exposed wire ends of the connector to get the injector's internal resistance value. Easy-peasy.
If the fuel injector's resistance is within 11 to 18 Ohms (1997-2009 4.6L and 5.4L V8 E-Series vans), the next step is to visually verify the fuel injector's spray pattern. I'll explain how to do this in the next test section.
Alright, here's the test:
- 1
Disconnect the fuel injector that you're gonna test from its electrical connector.
- 2
Place your multimeter in Ohms mode.
- 3
Measure the resistance across the male spade terminals of the fuel injector with the multimeter test leads.
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. - 4
Write this Ohms value down and record the number of the cylinder that fuel injector belongs to.
- 5
Repeat test steps on two other fuel injectors.
NOTE: The other two fuel injectors will give you a reading to compare to.
Alright, let's interpret your results:
CASE 1: The resistance value of the 'dead' cylinder's fuel injector is within specification. This result tells you that the fuel injector doesn't have an internal short-circuit or open-circuit problem.
Your next step is to check the fuel injector's spray pattern to see if it's clogged. Go to: PART 2: Checking The Fuel Injector Spray Pattern.
CASE 2: The 'dead' cylinder's fuel injector resistance is not within specification. Test this one injector again. If the injector registers the same Ohm value as before, this injector is defective.
