The Fuel Injector Test
There's a good chance that you already have one (or several) specific fuel injector you want to test or you don't know where to start.
If you want to test just one fuel injector or several, this will be your starting point. If you don't know where to start, I suggest you do a cylinder balance test to find out which cylinder is the one that's ‘dead’ and could possibly have a bad fuel injector.
If possible, do the fuel injector resistance test with a slightly warmed up. If your Dodge or Jeep SUV or pickup has been running for a while and it's hot, let it cool down for about an hour. If it's completely cold, crank up the engine and let it warm up for about 20 minutes.
Although having the engine warmed up helps to get a more accurate snapshot of the condition of the fuel injectors, it's not that critical.
So, if you have already removed the fuel injector or fuel injectors, or the vehicle cranks but does not start, etc., you don't have to install the fuel injectors and start the engine to warm her up. You can test them cold (and off of the vehicle).
Alright, here are the steps:
Unplug the fuel injector from its electrical connector.
- Disconnect the one that you suspect is bad and at least 2 others.
- You can test all of the fuel injectors if you want or need.
Place your multimeter Ohms mode.
- You'll be measuring the internal resistance of the fuel injectors in a few moments.
Probe the fuel injector's two male spade terminals with the multimeter test leads.
- In case you're wondering, it doesn't matter which test lead (black or red) you use on which terminal on the fuel injector, since the polarity doesn't matter in a simple resistance test.
Write down the Ohms (resistance) value that your multimeter is registering on a piece of paper. Write down what engine cylinder that fuel injector belongs to, too.
- Now, repeat the above steps on the remaining or other 2 fuel injectors.
Interpreting The Results Of The Fuel Injector Test
Before taking a look at what your results mean, I want to tell you that it's normal for the fuel injector resistances to vary a bit. For example, if you were to get the following resistances:
- 13.5 Ω for Injector #1
- 14.5 Ω for Injector #2
- 13.9 Ω for Injector #3
The difference in the above resistance values would be normal since they are small and not drastic (the values are hypothetical and won't reflect what you'll get on your particular vehicle).
What would accuse the fuel injector as being bad would be if the following values were recorded:
- 2.5 Ω for Injector #1
- 14.6 Ω for Injector #2
- 13.9 Ω for Injector #3
The resistance for injector #1 would be a dead give away that it's fried because its resistance value is way too radically different from the rest.
OK, choose from one of the following test results:
CASE 1: All tested fuel injectors registered about the same resistance values. This confirms that the fuel injector your are testing is OK.
CASE 2: One of the four fuel injectors registered a completely different resistance value. This indicates that the fuel injector is bad. Replace the fuel injector.
Should I Test All Of The Fuel Injectors?
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 4.7L Dodge or Jeep SUV or pickup 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.
I work in an automotive repair shop and sometimes our professional auto repair data information does not include the fuel injector resistances. So what I do is check at least 3 other fuel injectors, besides the one I suspect is bad, to get the average fuel injector resistance and go from there.