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AEM Infinity Injector Trigger Puzzle

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AEM Infinity 506


FIC 850cc Low Impedence Injectors with a ballast resistor wired into it.

Problem: The injectors don't seem to be opening. I have put the AEM Infinity into Diagnostic mode and have triggered the injectors manually. I do not hear any clicking when triggering the injectors.


1. 12V is read using a voltmeter on the ballast side of the injector wiring.

2. 5-8V is read on the ECU wire side of the injector (depending on the injector and possibly length of time ecu is on) I've gotten different voltage readings on same injector.

3. when reading the voltage on the ecu side of the wire and triggered half the time a .5v drop is seen on the reading. this does not happen every time.

4. Using a test light on the ecu side pin of the injector plug. Light is wired to 12v power and other side touching ecu pin. When trigger pressed in diagnostic mode of ecu I can see a light however it is extremely dim. I actually didn't notice the light the first couple times.

5. I wired the Engine Harness Myself!

6. Early in the install of the ecu when testing my wiring. I forgot to connect the engine ground but put power to the ecu. I am wondering if it I possibly fried a circuit on the ECU.

I have attached my wiring documentation. I have double checked continuity on all connections.

Attached Files

2. Seeing 5V-8V at the ECU's injector pins is not normal. Both of the injector's wires should be 12V most of the time, and the ECU will pull one of those wires down to 0V briefly to activate the injector. Be sure the ECU is receiving 12V power at pin C1-68, the injector driver circuits won't work properly without this.

3. The ECU triggers the injectors for about 5 milliseconds when you press the 'trigger' button in the software. Most multimeters show a smoothed/averaged reading when measuring DC voltage , so you're not going to see the voltage readout change from 12V to 0V when an injector is triggered. As an example, try using your multimeter to measure your the injector wires on another (port-injected) car while the engine is idling. Don't try this on a Direct Injected car, the voltages are different.

4. This might happen if the ECU is not receiving 12V power at pin C1-68. It's also possible the injector circuit isn't working properly, see below.

5. Your harness spreadsheet is inconsistent about whether RSTR.1 connects to BODY1.3 or BODY1.6, good idea to double-check this and update the doc to match the harness.

6. If you've confirmed the ECU is receiving 12V power at pin C1-68 but the injector outputs aren't working correctly, you may have damaged the circuits inside the ECU. It's difficult to say which wiring problems will actually damage hardware based on internet conversations like this. Email or call AEM tech support directly, they can get you info about pricing and turnaround time for having an ECU inspected. The contact info is on the paperwork that came with your ECU, and on the aemelectronics.com website. If you've already emailed or called them, please wait for them to reply rather than sending a second email. Our guys work 5 days a week, and it can take some time to get caught up on emails and voicemails that had been left during the weekend.

Another thing to try is double-check the injectors click if you briefly tap the trigger wire to ground. Don't do this while the trigger wire is connected to the ECU, remove the wire from the ECU harness and briefly tap it to ground. I've heard of injectors getting stuck if they sit for long enough, even brand new ones. Be sure the ballast resistor is still connected, it's rare but possible to damage a low-impedance injector by sending it too much current.

Hope that helps,


Thank you so much for this response. I was able to find the problem. The resistor wasn’t being powered! I had wired up pin 8 instead of pin 1 by accident. That phantom 5v 8v power must have been coming from the resistor. All the power being pushed through the connected injectors. I was able to fire up my car and begin the tuning process. So far I just have one more mystery to solve. Again thank you so much for the help.

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