How To Test The Fuel Injectors (Dodge 3.9L, 5.2L, 5.9L)

In this article, I'll show you how to test for a bad Dodge 3.9L, 5.2L, 5.9L fuel injector with a multimeter.

It's rare for fuel injectors to go bad, but that doesn't mean it doesn't happen and when it does you'll have a rough idle / misfire condition on your hands.

You can find this tutorial in Spanish here: Cómo Probar Los Inyectores De Combustible (Chrysler 3.9L, 5.2L, 5.9L) (at: autotecnico-online.com).

Symptoms Of A Bad Fuel Injector

As you might already be aware, every cylinder in your 3.9L V-6, 5.2L V-8, or 5.9L V-8 needs 3 very important things to work. These are air, fuel, and spark. If one of these is missing from the mix, you'll have a ‘dead’ cylinder on your hands!

The fuel injectors are the ones task with delivering fuel to the cylinder, and so, when one engine's cylinder's fuel injector stops injecting fuel, that specific cylinder will go ‘dead‘. When this happens, your 3.9L, 5.2L, or 5.9L pickup, van, or SUV will experience one or several of the following:

• Engine will have a rough idle.
• Engine will misfire under load, especially when you accelerate your vehicle.
• Lack of power when accelerating your pickup, van, or SUV.
• Bad gas mileage.
• Since your 3.9L, 5.2L, 5.9L vehicle is OBD II equipped, you'll usually see a misfire code (P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308) lighting up the check engine light on your instrument cluster.

So, what causes a fuel injector to go bad? It's usually just old age, although not always. Which leads up to the 3 main types fuel injector failure:

1. Fuel injector doesn't spray any fuel because it has fried internally.
2. Fuel injector sprays fuel, but not enough (clogged fuel injector).
3. Fuel injector stuck On all of the time (as soon as the key is turned On). This is usually, but not always due to a bad fuel injection computer.

This article focuses on the most common, which is when the fuel injector doesn't spray any fuel at all due to an internal short circuit and a clogged fuel injector.

What Tools Do I Need To Test The Fuel Injectors?

To test the fuel injectors in your Dodge 3.9L, 5.2L, or 5.9L you don't need any expensive tools.

Here's a basic list of tools you'll need to test all eight fuel injectors:

1. A multimeter.
   • You'll only be using the multimeter to check resistance (Ohms).
   • 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).
2. Scan tool.
   • 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.
   • Don't have one? Check out my recommendation: Abe's Scan Tool Recommendation.
3. Pen and paper to write down your fuel injector resistance test results.

TEST 1: Fuel Injector Resistance Test

The engine in your Dodge pick up (van or SUV) should be warmed up. If your vehicle doesn't start, don't worry about this.

The following test steps assume that you're gonna' test all of the fuel injectors but you don't have to. If you're just wanting to test one fuel injector, my recommendation is to test at least two others for the comparison values you'll need at the end of the test.

NOTE: One last thing, the following instructions also apply to the 3.9L V6 even though the instructions refer to 8 fuel injectors.

OK, to get started, this is what you need to do:

1. 1

   Disconnect the fuel injector from its electrical connector and set your multimeter to Ohms mode
   
   Now measure the resistance of the fuel injector.

2. 2

   After verifying the resistance value, write it down on a piece of paper. Don' forget to write down what cylinder that reading belongs to.

3. 3

   Now, repeat test steps 1 through 2 on the remaining 7 fuel injectors (don't forget to write down the resistance values).

4. 4

   By this point you should have 8 resistance values written down (or 3 if you're not testing them all). The next step is to interpret these values to find out if you have one that's fried.

To interpret the results of your test, please read the section: Which Fuel Injector Do I Test First? Or Do I Test All Of Them? first and then come back here.

CASE 1: The resistance value of all 8 fuel injectors is the same. This result indicates that the fuel injectors are not fried. The cause of the misfire condition or misfire codes or rough idle condition lies somewhere else. Go to the last part of this section for more testing options.

There's a good chance the fuel injector may be clogged. If so, the only way to test this at home is swapping fuel injectors with another already on the fuel rail. So, I suggest doing one more test. Go to: TEST 2: Swapping Fuel Injectors.

I also suggest the test in this section: Fuel Injector Diagnostic Strategy for more troubleshooting ideas.

CASE 2: One (or more) fuel injector value is totally different from the rest. Retest the fuel injector that was not within the stated specification. If the resistance value is still the same and drastically different from the normal resistance value (or different from the rest of the fuel injectors), that fuel injector is bad. Replace the fuel injector.