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AEM EMS4 Timing and Trigger Polarity

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Hi guys,

This is my first time tuning a standalone ECU on a Honda Prelude H22 and I have to say very hard in comparison with ECU reflashing.

I decided to make my own harness instead of buying a PnP one for my EMS-4, this way I will understand more about ECU connections. I followed all the HPA steps and after a lot of free nights I started up my car.

So my car is idle perfectly, I checked my timing at cranking before starting the car and it matched with my laptop, my AFR is stable until I get 3000-3500 RPM when my car starts bogging or shutting down. So after some attempts I took my timing lamp to see if my timing at idle was matching my laptop and certantly it is. If I rev my car more than 2000 rpm, my timing becomes unstable and as far as I get to 3000 rpm I cannot even see the timing mark on my crank. Actually, I tried to fix it playing with the "Pickup Delay Comp" parameter with no luck.

On the "Setting Base Ignition Timing - Post Startup" you said it could be a wrong polarity in my trigger sensors but my question is about the EMS-4 harness.

It only has 2 pins, 1 for cam sensor mag and 1 for crank sensor mag (picture 1), and only 1 common ground pin. My car harness has different pins for cam/crank signals and cam/crank ground signals (picture 2). So I connected terminal number 2 (picture 2) to EMS-4 pin 22 (picture 1) and terminal 4 (picture 2) to EMS-4 pin 21 (picture 1). Because EMS-4 only has 1 ground pin I connected terminal 12 and 14 (picture 2) to EMS-4 pin 19 (picture 1).

My cam/crank sensors are MAG Rising Edge according to AEM base calibration. I do want to solve my issue without damaging anything on the ECU so, do you thinkg it will be safe to reverse polarity of these sensors? or trying with MAG Falling Edge configuration? (picture 3)

Thanks in advance.

Ok if you have wired the ECu as per your diagram then it would be typical for the trigger pattern to be a falling edge trigger. Selecting rising edge trigger would give you the effect you're seeing as it is effectively the same as having the polarity reversed. Try selecting falling edge for both triggers and test again. You will need to adjust your base timing when you make this change though.

Hi Andre,

Actually, changing my Crank MAG sensor configuration from Rising Egde to Falling Edge solved the issue. Also, I tried changing my Cam MAG sensor as well but didn't work so I left it set as Rising Edge.

So now, my timing is stable along my RPM range and no timing errors. But my car keeps stutteding, shaking and weak acceleration when I fully press the throttle. I also thought that it might be something related to my injectors because at full load it gets too rich or too lean, I cannot even drive the car so I checked the "injector offset vs battery volts" table according to AEM base calibration and it was a small difference according to my injectors specs but still with the same issue.

Then, check my "Injector phase" and adjusted exactly to 0ยบ degrees at TDC exhaust stroke according to AEM procedure (picture attached), but I'd like you to explain to me how can I adjusting the "injector advance" table because AEM base calibration could be a little wrong as well. I know, injectors should open right after TDC exhaust and close before BDC intake, right? but how can they affect my engine by advancing o retarding?

What else do you think it might be causing this issue?

Thanks in advance.

I'd be very surprised if the injector timing is your issue. Unless you have very large injectors fitted to the engine, injector timing normally has the most effect at idle and low rpm/cruise. At high rpm/high load the injector duty cycle tends to be quite high so ultimately the injector is open for most of the engine cycle anyway so moving the timing of the injection achieves little. There are also two schools of thought about injector timing - One is to inject when the intake valve is open so the fuel makes its way straight into the cylinder and the other is to inject against a closed valve so that the heat of the intake port and valve vapourises the fuel.

Is your fuel map correctly calibrated? I'd be inclined to think that is where your issue is likely to be. Is the problem noticeable just during a throttle transient or any time your at WOT? Does the engine tune up correctly? Is it responding to tuning changes as you'd expect? What sort of ignition timing are you using?