Checking to see if a fuel injector has failed, and causing your 3.2L equipped Isuzu to misfire or idle rough, isn't a hard test to do.
When a fuel injector fails, it's usually due to the fact that its internal coil winding has suffered a short-circuit problem or an open-circuit problem.
For you and I, this means that we can use a multimeter (in Ohms mode) to check the fuel injector's resistance and find out if its bad (or not).
The fuel injectors have a factory resistance specification and in this tutorial I'll show you how to test them.
Contents of this tutorial:
Symptoms Of A Bad Fuel Injector
Fuel injectors can fail in one of several ways. Here are some of the most basic types of fuel injector failures:
- The fuel injector's internal winding suffers a short-circuit problem or an open-circuit problem. This causes the fuel injector to stop injecting fuel.
- The fuel injector becomes clogged and doesn't spray correctly or not enough fuel.
- It comes on and does not turn off (due to electrical issues). In other words: it does not pulse on and off but stays on all of the time spraying a tremendous amount of fuel as soon as you turn the ignition key to the ON position.
The symptoms of a failed fuel injector are pretty much the same ones no matter how it fails. These symptoms are:
- Rough idle.
- Lack of power.
- Hesitation when you accelerate your 3.2L Isuzu Amigo (Rodeo, Trooper or Honda Passport) down the road.
- Misfire trouble codes (OBD II equipped only):
- 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.
The focus of this tutorial is to see if the fuel injector's internal coil has failed (and thus causing the fuel injector to stop injecting fuel), but testing for a clogged injector isn't that much more complicated and I'll show you how in the next page.
Checking The Injector's Internal Resistance
To find out if any one of the fuel injectors in your Isuzu are fried... we're gonna' check the resistance of their internal coil winding.
If the fuel injector is bad, this coil winding will have a short or an open.
As mentioned at the beginning, this is a very easy test that can be accomplished with a simple multimeter. The multimeter will set to its Ohms (Ω) mode to check the injector's resistance.
By the way, the instructions below call for testing all 6 fuel injectors on your 3.2L V6 equipped Isuzu Amigo (Rodeo, Trooper).
IMPORTANT: On the 1993 to 1997 Isuzu SOHC 3.2L engines, the upper intake manifold plenum must be removed to access the fuel injectors. If your specific 3.2L Isuzu falls into this category, take a look at the following section: Fuel Injectors Under the Intake Manifold Plenum.
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:
Disconnect the fuel injectors from their harness connectors.
NOTE: To identify which cylinder the fuel injector belongs to, see the above illustration with the cylinder # id for the 3.2L Isuzu V6.
Set your multimeter to Ohms (Ω) mode and:
measure the resistance of the fuel injector across its two male spade terminals with the multimeter test leads (see the illustration in the image viewer).
Write down the resistance value that your multimeter records for the specific fuel injector you're testing. The illustration above will help you identify the cylinder # the fuel injector belongs to.
Repeat steps 1 through 3 on the remaining fuel injectors.
NOTE: The Isuzu fuel injector factory manual resistance specification is: 11.8 to 12.6 Ohms.
Let's find out what your specific multimeter test results mean:
CASE 1: All fuel injectors registered the same resistance values. This confirms that the fuel injector you're testing is OK.
Here's why: If any one of the fuel injectors were bad, your multimeter would've registered a completely and totally different resistance value (for that fuel injector). Since your resistance (Ohms) value were the same for all, this is an indication that the fuel injectors do not have an internal electrical fault.
CASE 2: One of the fuel injectors registered a completely different resistance value. This indicates that the fuel injector is BAD. Replace the fuel injector.