Fuel injectors rarely go BAD, but when they do, they will cause the engine in your Jeep 4.0L Grand Cherokee (or Cherokee or Wrangler) to miss and/or idle rough. The really cool thing is that they can be easily tested with a multimeter and this article will show you how to do a simple fuel injector resistance test.
Depending on the year of your specific Jeep (1995 and newer), a BAD fuel injector may or may not set a specific fuel injector diagnostic trouble code (DTC) like: P0201, P0202, P0203, P0204, P0205, P0206. In most cases, all you'll see code-wise are misfire codes: P0300, P0301, P0303, P0304, P0305, P0306.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar los Inyectores de Combustible (4.0L Jeep) (at: autotecnico-online.com).
To successfully accomplish the tests in this article, here are some important tips:
TIP 1: The engine in your 4.0L Jeep Cherokee (Grand Cherokee, Wrangler) needs to be at operating temperature to get an accurate snapshot of the condition of the fuel injectors.
TIP 2: If your Jeep doesn't start, you don't have to worry about performing the test with a warmed up engine.
The Fuel Injector Resistance Test
What makes testing the fuel injectors on your Jeep's 4.0L 6 cylinder engine is that they are in plain view and easy to get to.
This makes it possible to check for a bad fuel injector in about 10 to 20 minutes.
Now, to give you an idea of what's involved in testing for a bad fuel injector... we're going to simply check the internal resistance of each fuel injector and compare it to the factory spec.
You can either use a digital multimeter or an analog multimeter for this test.
Alright, here are the steps:
Disconnect the fuel injectors from their electrical connectors.
Grab your multimeter and select Ohms mode on the multimeter's dial.
If you're gonna test them all, probe the #1 fuel injector's two male spade terminals with the multimeter test leads.
Whatever Ohms value your multimeter throws at you, write it down on a piece of paper.
The fuel injector resistance should be within 13.3 to 15.7 Ohms (1991-95) or 10.8 to 13.2 Ohms (1996-2001). If your reading is different, don't panic... write it down and continue testing the other 5 fuel injectors (you'll see why when you interpret the resistance value of all six).
Now, repeat steps 1 through 5 on the remaining fuel injectors.
Let's find out what your specific multimeter test results mean for your 4.0L Jeep Wrangler (or 4.0L Cherokee/Grand Cherokee):
CASE 1: All fuel injectors registered the same resistance values. This confirms that the fuel injector your are 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.
Which Fuel Injector Do I Test First? Do I Test All Of Them?
You don't have to test them all, if you don't have to. This is especially true if you have a repair manual for your specific Jeep SUV and that repair manual has the fuel injector resistance specification.
The main reason I suggest you test them all is to avoid having to search for the resistance value, either online or in a book. Now, don't get me wrong... the more info you have at your disposal, the better. But, if you test them all... you'll find out what the average Ohms value is without having to look it up.