AEM EMS Tutorial Notes

[Intropy]

Another question:

I just bypassed my resistor pack and noticed in the wizard they have injectors listed with <P&H DRIVER> and then the rest just have their brand/model, high or low impedance. Is there a setting that tells the driver to operate as P&H or saturated? Or does it only operate as P&H? It lists the stock 3000gt injectors as 3ohm. I assume any low imp injector listed without the prefix <P&H DRIVER> was tested with a resistor pack inline to produce battery offset numbers that were meant for use in the series 1 box with its saturated driver...?

Injector Latency / Battery Offset Primary / Injector Drivers (Peak & Hold)

The driver on the EMS is always peak & hold. Deleting the resistor pack lets you take advantage of this. Yep, any injector listed in the setup wizard that is not prefixed with <P&H Driver> is intended for use with the resistor pack. If you delete it, you'll want to choose the closest P&H driver.

Now that being said... unless you are just lucky enough to be running one of the 10 or so injectors listed in the wizard, you're going to need to be critical of the values. Remember that with P&H, the resistors are gone and the EMS supplies full battery voltage to the injector until the desired current level is reached, at which point it backs down. This is obviously going to change the way the injector responds at different battery voltages and thus require a change to the Batt Offset Primary table. When you select a P&H injector in the wizard, that table is the ONLY thing you are changing (well, and Inj Size, which is only used by wizards). So the question is really how to make sure your offset values are right. You have 4 options:

1. Use a value published online, if available.
2. Get AEM's approval to mail your injectors to them for testing. They'll give you an offset table.
3. Pay someone to do it.
4. Do it experimentally.

I don't recommend option 4, but if you're just trying to get a car running and tuned, what you want to check is that changes to your fuel map behave as expected.

Batt Offset Primary adds a duration (observable in the channel Fuel Trim Bat-Pri, in mS) to your injector pulse for a given voltage. Let's say that the correct pulse for a given RPM, load, and desired AFR is 4ms (observable in Fuel Inj 1 Pulse). You're at 14v and the Batt Offset Primary table is 0.5ms at 14v. This means it is adding 0.5ms to your pulse. If it was 0, your pulse would be 3.5ms.

In order to know if that's right, you obviously need another data point. Say our AFR in the above example was 13.2. Let's try to make it 12. So we need to remove 9.1% in that cell (12 / 13.2 = .909). You can do this easily by choosing that cell in AEMTuner and pressing 'E', then '-9.1', 'Enter' (or AEMPro style, you enter 90.9).

If you don't get the desired AFR, you need to adjust Batt Offset Primary (and your fuel map) until you do. When you get predictable results from changing your fuel map at various locations, you know you're close. Obviously, this can only be done with any sort of precision on a dyno, and you can really only do it for the operating voltage ranges of your car.

[Intropy]

A question.

I want to hook up a switch to activate logging. I'd like to use my cruise control switch. There is a wire that is 12v switched on. Can I attach that 12v to a lowside(ground switched) input? I assume I would need to put a small resistor on that line to act as load? Or am I doing it wrong? The other way I was thinking was using that 12v source to activate a relay that is just connected to ground on one end and switch input on the ems.

I can't remember how the cruise control switch is wired but you can certainly use it. One side must go to ground. The other side will be wired to one of the AEM's high side switch pins, such as switch 5 (pin 107/37) or switch 6 (pin 114/44). Then select that as your switch input in the ECU Internal Logging setup screen. No resistor necessary.

The way AEM lists switch input options is a little confusing - it will be either:

• GND=ON - this is the "normal" option, which means that the software switch is on when the hardware switch is closed.
• 12V=ON - the opposite: the software switch is on when the hardware switch is open ("floating").

[Memphetic]

Thanks, I need a wiki so other people can edit it.

You can put this on my wiki. FrozenApps Wiki

[SpikeyGG]

Intropy, this is an awesome thread. Thanks for posting it so long ago. I made a post on 3SI about a month ago asking for these types of details, one guy responded. He basically said: "don't ask here because no one knows." Anyway, I wanted to thank you because it gives me some idea of which cylinder I see as knocking -- very useful thread.