...Continued from the previous page.
After testing the resistance of the fuel injector, write down the Ohms number (value) that your multimeter registered on a piece of paper. Use the image in the image viewer (of the previous page) to write down the cylinder number this reading belongs to).
For the moment, don't worry about what the resistance value should be of each fuel injector. Now, repeat test steps 1 through 3 on the remaining 3 fuel injectors.
Interpreting The Results Of The Fuel Injector Test
OK, now we're gonna' interpret the results of your fuel injector resistance (Ohms) readings... choose from one of the following CASES:
CASE 1: All of the multimeter resistance values are nearly identical. This result indicates that the fuel injectors are not fried internally and are not causing the misfire code or condition.
Now, your vehicle may still be misfiring... my suggestion to you is to check that each cylinder is getting spark and that each has good compression. The following tutorial will help you do (and interpret) the results of an engine compression test:
CASE 2: One of the 4 multimeter resistance values is drastically different: Test all fuel injectors one more time, just to confirm the initial resistance values your multimeter registered. If they are the same as before, then the fuel injector that registered the different resistance value is bad. Replace the fuel injector.
Now, to be a little more specific, let's say that you got the following resistance values:
- Cylinder 1: 12.6 Ohms (similar)
- Cylinder 2: 12.4 Ohms (similar)
- Cylinder 3: 12.7 Ohms (similar)
- Cylinder 4: 8.6 Ohms (different)
Cylinder 4 is the one that is fried, since the resistance value is too great to be considered similar to the other three. Keep in mind that the above values are the ones that you are gonna' see on your specific Nissan vehicle, I'm using them to illustrate what differences you should be looking for.
Which Fuel Injector Do I Test First? Or Do I Test All Of Them?
The biggest reason you should test all of the fuel injectors on your 2.4L Nissan Altima (Frontier, or Xterra), is that you'll get a clear idea of what the average resistance value of each fuel injector should be.
This becomes especially handy (knowing the average resistance of all the fuel injectors) if you don't have a repair manual with the fuel injector resistance specification.
Why does this test work? Well, it's because all fuel injectors have a specific internal resistance that can be measured in Ohms mode on a multimeter. When a fuel injector goes bad, it'll normally have a completely different resistance value than the other ones.
Therefore, the purpose of the test is to find the bad fuel injector by reading its resistance and comparing this reading to at least two other fuel injectors. And since no specific resistance specification is given to compare against, it's important to test them all to find out the average resistance value of them.
My Nissan Doesn't Start
In many cases, the vehicle doesn't start. Specifically, it ‘Cranks but Doesn't Start’ and this may make you think that the fuel injectors are bad.
In this section, I'll explore some of the things you need to check to get to the bottom of this No Start Problem...
... because it is next to impossible to have all 4 fuel injectors go bad (unless someone put sugar in your gas tank and they are clogged, this does happen).
Here are a few things you need to check:
- Do a Fuel Injector Noid Light Test.
- In this test, you insert a Noid Light into the fuel injector's connector and then have someone crank the engine for you as you watch for the Noid Light to blink On and Off.
- If the Noid Light flashes (blinks) On and Off, then you now know that the fuel injector is getting both power and Ground (in other words, it's being activated by the PCM).
- If the Noid Light does NOT flash ON and OFF, then you need to make sure that you have voltage in one wire and that the PCM is Grounding the other.
- 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).
- Check for Spark and Fuel Injector Pulses (with a Noid Light).
- Performing these two tests on ALL of the 4 engine cylinders on your Nissan is important because if you don't have spark AND fuel injector pulses (as checked with a Noid Light), then the crank sensor is bad.
- Check Fuel Pump Pressure.
- If the fuel pump doesn't work and you spray starting fluid into the engine, IT WILL START.
- This may make you think the fuel injectors are bad, when it's the fuel pump causing the No Start Problem.
In the next page you'll find some more thoughts on how to diagnose a bad fuel injector.