How To Test The Fuel Injectors (2.4L Mitsubishi)

How To Find The Bad Or Clogged Fuel Injector

Finding out if a bad fuel injector is the cause of the rough idle (misfire) may seem hard/difficult but it isn't. There's a logical process that we can use to find out what's causing the problem (and see if it's due to a bad fuel injector).

The very first thing that you and I need to do is to find out which cylinder is the 'dead' one. By 'dead' I mean misfiring. Once the misfiring cylinder has been pinpointed then the rest is easy.

OK, below are the diagnostic steps I take when trying to diagnose a bad fuel injector:

1. Find the 'dead' cylinder first.
   • This is easily accomplished by checking for misfire codes (P0301, P0302, P0303, P0304) with a scan tool or code reader.
   • If no codes are registered, the next step is doing a cylinder balance test to find the 'dead' cylinder.
2. Check all 4 ignition coils for spark.
   • It's important to make sure that each cylinder is getting spark with a dedicated spark tester.
     • This tutorial will help you test the ignition coils: Ignition Coil And Crank Sensor Tests (1.8L, 2.4L Mitsubishi).
   • It's important that you check that the spark plug boot and spark plug are NOT soaked (or swimming) in engine oil.
   • You should also remove the spark plugs and check them 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.
3. Check engine compression.
   • After making sure that each cylinder is being fed with spark (and thus eliminating the ignition system as the cause of the misfire), the next step is to check for low engine 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 Test The Engine Compression (Mitsubishi 1.8L, 2.4L).
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.
   • If I've found out that I have a specific 'dead' cylinder and:
     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 and...
     4. I think the fuel injector is clogged, I then swap out that fuel injector with its neighbor.
     If the misfire now follows that swap then I now know that fuel injector is clogged (or bad) and needs to be cleaned or replaced.

It looks a like a long list but it will help you to find out the exact cause behind the misfire problem. What will help you save a lot of time, money and frustration is to first find the 'dead' cylinder. Following the above diagnostic strategy has saved my lunch quite a few times and I think it'll help you too!

More 2.4L Mitsubishi Tutorials

To see all of the 2.4L Mitsubishi specific articles, go to: Mitsubishi 2.4L Index Of Articles.

Here's a sample of the articles, you'll find in the index:

• How To Test The Throttle Position Sensor (2.4L Mitsubishi).
• How To Test The Engine Compression (Mitsubishi 1.8L, 2.4L).
• Testing A Bad Alternator: Symptoms And Diagnosis.
• How To Bench Test The Starter Motor.
• Blown Head Gasket Test (Mitsubishi 1.8L, 2.4L).