Load Testing Fuel Injectors

[97ranger4x4]

I have a couple of questions.

I just had the shop diagnose my truck since I couldnt do it myself with the help of my GF stepdad. Basically I had a P0300 random Misfire, P0303 Cyl 3 Misfire, P0305 Cyl 5 misfire, P0174 Bank 2 Lean codes.


He said that the injector on Cyl 5 was causing the misfire. He said cyl 3 isnt misfireing and if I clear the CEL, it should come back without the Cyl 3 misfire.

He said he did a relative compression test and it passed twice.

He said when I take off my intake he said to check for shorts within the wireing. He said when he had it hooked up to their monitoring system, the injector was going back and forth between working and not. I think the injector itself is fine it might just be a bad connection. Note I replaced all 6 injectors with OEM motorcraft injectors 3 months ago. I also replaced all 6 plugs with motorcraft plugs and new wires.

But none the less, I need to know how to test the wires for the injector? I have the factory service manuals at home, but I figured it would be best to post here where some great minds can give input.

When I get home I will grab my service manuals and read up on what the procedure is for testing the injectors.

 

[97ranger4x4]

bump

 

[feellnfroggy]

To test teh wires for go get a continuity tester. A voltmeter/ammeter will also tell you how much elctricity is flowing through when the injector is activated.

With the two of these tools it should give you enough info to figure out what you need to know with the wiring.

 

[97ranger4x4]

Well I looked in my GF stepdads service manuals and saw that the injectors should be between 11-18 ohms. We both have voltmeters but I will need to see what a continuity tester is and how to use it.

So my questions is, the shop manuals dont tell me how to test the injectors. Do I just take the injector out with the truck off and just put one lead on one pin, and the other lead on the other pin to measure the resistance for that injector? Unfortunately I have to take the whole intake plenum off so there is no way to have the truck running. Assuming the injector is within the 11-18 ohm spec. how would I test for a short in the wiring?

Thanks,
Keith

 

[JeffWS]

The two wires at the injector are a 12 volt constant (w/key on), and a ground that is controled by the computer. A noid light is used to see if the wires are working. You may use a test light too. The light should flash while cranking, if the engine is running it would flash very fast.

 

[97ranger4x4]

So I picked up a noid light at Napa today. So if I understand this whole process correctly I should:
1. take off the Intake Plenum and all of the necessary electrical connections.

2. Take an ohm meter and check the resistance between the two pins on the injector with the truck off. If within spec of 11-18 ohms, then the injector is working fine.

3. Take the noid light, and connect it to the fuel injector harness and crank the motor over without turning on. If getting the proper signal I should see a flashing Noid light. If the light does not flash or stays on (no flashing) then I have a problem further down the line.

4. Replace injector if bad, or track down further wireing issues. reasemble intake plenum and enjoy a truck that is running correctly!

Did I miss anything?

 

[JeffWS]

The injector resistance should be between 11-18 ohms, but they should be real close to each other.
You can test the injectors with the engine running by using a long screw driver. Place the driver on the injector and the handle against your ear. You will hear the injector opening and closing, and they should sound the same.

If you can remove the injector wire wo/pulling the intake, do so.

Let us know the results.

 

[97ranger4x4]

There is no way for me to pull the injector wire with out taking the intake off. This will be the third or 4th time taking the intake off so its not that big of a deal. I have a mechanics stethescope that I can place on the injector at idle and listen to it open/close and compare it with others. That might save me from taking it all apart.

thanks for the input. I will be working on it Friday-Sunday since I have those days off.

 

[97ranger4x4]

Okay so I just did an OHM resistance test on the #5 injector (which is supposed to be bad) and it read around 5 ohms. I did # 6 and it read 15 ohms. According to the factory manual, it should be between 11-18 ohms. So 15 sounds like it is right in the money.

So I called up Autozone and they can get me a GP Sorenson fuel injector for like $43 and the ford dealership can get me a motorcraft injector for like $99. The GP sorenson has a 1 yr warrenty. I just replaced these injectors like 3 months ago with Motorcraft So I am kinda pissed that it went out early. How important is it to have motorcraft injectors? Anyone use GP Sorenson?

 

[JeffWS]

I have not used the GP injectors.
My only concern with another type injector is that if the resistance value is different and it allows a different amount of fuel into the cylinder, the fuel mixture (trim) won't be as accurate. You might want to ohm test the GP injector before you buy one.
Try to return the Motorcarft injector.

 

[97ranger4x4]

I ended up just paying for the motorcraft. I said F this, I dont wanna do this again. So I will call up Rockauto where I bought the injectors and try and return it.