Testing a fuel injector on a 2.4L Quad 4 engine is a pretty easy affair, since they are in plain view and easy to get to (after taking off a few things, that is). This article will help you to do a simple resistance test of the fuel injectors with a multimeter. You don't need a scan tool or any other expensive or exotic test equipment to follow the step-by-step instructions in this article.
Now, it's pretty rare for a fuel injector on a Quad 4 engine to go BAD, but that doesn't mean that they don't. What sucks when one does go BAD, is that the fuel injection computer usually doesn't set a fuel injector diagnostic code... it usually sets a misfire code (P0300, P0301, P0302, P0303, P0304) which will lead you to believe that the problem lies in the ignition system.
Contents of this tutorial:
Tools You'll Need:
- Pen and Paper
Symptoms a BAD Fuel Injector
The OBD II PCM on your 2.4L Quad 4 equipped vehicle has the capability to set a fuel injector diagnostic trouble code, but it rarely does:
- P0201 -Cylinder 1 Injector Circuit Malfunction
- P0202 -Cylinder 2 Injector Circuit Malfunction
- P0203 -Cylinder 3 Injector Circuit Malfunction
- P0204 -Cylinder 4 Injector Circuit Malfunction
What you will see is normally a misfire code (but not always):
- P0300 Random/Multiple Cylinder Misfire Detected.
- P0301 Cylinder 1 Misfire Detected.
- P0302 Cylinder 2 Misfire Detected.
- P0303 Cylinder 3 Misfire Detected.
- P0304 Cylinder 4 Misfire Detected.
What you'll definitely see is a rough idle condition and one or more of the following conditions:
- Bad gas mileage.
- Engine will run with a ‘dead’ cylinder... in other words, it will idle rough.
- Engine will have a miss when you accelerate the vehicle.
- Black smoke coming out of the tailpipe.
- Won't pass the yearly emission verification test.
Testing The Fuel Injector With A Multimeter
If your car starts and runs, I suggest you test the fuel injectors with the engine warmed up. If your Chevy, or Pontiac, or Olds, or Buick 2.4L Quad 4 equipped car doesn't start... you don't need to worry about this.
Usually, if a fuel injector does go BAD on your car, it will be only one out of the four (although this is not an absolute truth)... Still, I suggest you test all four and the following test instructions assume that all 4 fuel injectors will be tested.
Alright, here are the steps:
OK, to get started, disconnect all four fuel injectors from their electrical connectors.
Grab your multimeter and set it in Ohms Mode and probe the #1 fuel injector (or whatever fuel injector that you want to test) with the multimeter test leads.
If you don't have one and need to buy one, take a look at my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
Your multimeter will register a resistance value, whatever this number is, write it down on a piece of paper, along with the number of the cylinders this reading belongs to. You'll be using this resistance value to compare it to the other three in a few moments.
If you don't know the numbers of the engine cylinders, use the image in the photo viewer as an aid.
The average fuel injector resistance value will be about 12 Ohms. These Ohms values may not be exactly what the fuel injectors will register on your car, if this happens, don't worry too much about this. You'll see why in the interpretation of your test results in CASE 1 below.
Let's take a look at what your test results mean:
CASE 1: All of the multimeter resistance values are nearly identical: This resistance test result means that none of the fuel injectors are fried electrically. The cause of your rough idle or misfire condition is due to another reason.
Here's why: When a fuel injector does fry electrically, the resistance value that the multimeter will register for this fuel injector will be radically different than the values that the multimeter will register for the others.
CASE 2: One of the four multimeter resistance values is drastically different: Re-test that fuel injector once again and if the multimeter registers the same value as before... then that fuel injector is fried and needs to be replaced.