AEM F/IC writeup

Ok I think my theory about the current being split to ground is garbage. The resistor in this configuration does basically nothing. I measured the voltage the AEM sees with and without the resistor and it's identical, about 1.6V with just the ignition on, and about 2.2 at idle. There is practically no current running through these wires, so no amount of resistors is going to change the voltage, unless you set up a divider. Which means put another resistor in series with the first one to ground and tap between the two resistors. Look up voltage divider. I believe this is what they meant to put on the Miata diagram, and whoever drew it messed up and forgot the second resistor.

I also tried the bypass jumper that came with the AEM. The car started and immediately stalled. I then cut the resistor since I wanted to be sure I wasn't altering the MAF signal, and it still stalled. Then I plugged the AEM back in and it still stalled. I then measured the MAF output voltage and it was sky high 8.24V. Now I second guessed myself that maybe the resistor was lowering the voltage and I just measured the current incorrectly.

So I hooked the car back up stock and it started just fine, no CEL. Then I went to go measure the MAF output and my multimeter died on me. Fuse blew, and I couldn't find a replacement. I soldered some wire across the fuse terminals and it was still dead. It's fried. So I am done for today.

I have given some thought to this MAF situation. We really shouldn't be intercepting the MAF signal. The AEM can output 5.87V max, which is nowhere near the 12V max of our MAF. Even if you setup a voltage divider or use a potentiometer and get the signal within the AEM's range, you'll have to compensate with twice the fuel and you'll never be able to have a true base calibration.

I am curious what my CEL is. I am going to buy a scanner tomorrow when I buy a new multimeter. I am guessing it's a lean code since it took a couple minutes for the CEL to pop up. Could also be an O2 code, since I did not follow the AEM instructions and put an isolation resistor on the O2 wire. I think this is why I got a few 0's in my data log.

Hopefully, I'll get some more time this week to play with it.
 
jdwk said:
Ok I think my theory about the current being split to ground is garbage. The resistor in this configuration does basically nothing. I measured the voltage the AEM sees with and without the resistor and it's identical, about 1.6V with just the ignition on, and about 2.2 at idle. There is practically no current running through these wires, so no amount of resistors is going to change the voltage, unless you set up a divider. Which means put another resistor in series with the first one to ground and tap between the two resistors. Look up voltage divider. I believe this is what they meant to put on the Miata diagram, and whoever drew it messed up and forgot the second resistor.

I also tried the bypass jumper that came with the AEM. The car started and immediately stalled. I then cut the resistor since I wanted to be sure I wasn't altering the MAF signal, and it still stalled. Then I plugged the AEM back in and it still stalled. I then measured the MAF output voltage and it was sky high 8.24V. Now I second guessed myself that maybe the resistor was lowering the voltage and I just measured the current incorrectly.

So I hooked the car back up stock and it started just fine, no CEL. Then I went to go measure the MAF output and my multimeter died on me. Fuse blew, and I couldn't find a replacement. I soldered some wire across the fuse terminals and it was still dead. It's fried. So I am done for today.

I have given some thought to this MAF situation. We really shouldn't be intercepting the MAF signal. The AEM can output 5.87V max, which is nowhere near the 12V max of our MAF. Even if you setup a voltage divider or use a potentiometer and get the signal within the AEM's range, you'll have to compensate with twice the fuel and you'll never be able to have a true base calibration.

I am curious what my CEL is. I am going to buy a scanner tomorrow when I buy a new multimeter. I am guessing it's a lean code since it took a couple minutes for the CEL to pop up. Could also be an O2 code, since I did not follow the AEM instructions and put an isolation resistor on the O2 wire. I think this is why I got a few 0's in my data log.

Hopefully, I'll get some more time this week to play with it.
Click to expand...

Nice and useful information. Really would like to see what comes of this.

on a side note, has anyone tried using the MAF simulator MAP function of the FIC? you know.....where the there is no MAF and the internal MAP is translated into a MAF signal?

My hope is that all the FIC bugs get flushed out before I decide to get one. So technically you guys are my guinea pigs ;-P
 
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Glad to be of service haha. I agree with jdwk that altering the MAF signal is not the best way to tune the FIC. I am thinking maybe I should just reconnect the MAF wire so the FIC does not intercept it, and I bet the car would run fine. First, I'm going to consult tech support and see if they agree that it would be okay, but I don't really see how it wouldn't be. I think using the other fuel maps for the onboard MAP sensor and altering the injector pulse would be much more effective.
 
Just got off the phone with AEM, and it looks like swirlfx was on the right track. They told me to disconnect the MAG output negative (MagO-) wire and leave it disconnected so the FIC reads it but does not intercept the ECU signal. Then I was told to take the MAG output positive (MagO+) wire and switch it from a intercept to a tap connection (3 way connect, 2 ends of the ECU wire and 1 FIC wire). Now that I think about it, the MAF wire really shouldn't be doing anything to affect the ECU even with a resistor wired in. The only way it would alter the signal is if I were to change the map in the software, but for now it is all 0's and I have the mode set to percent so it is altering the MAF signal by 0% across the board which does nothing.

I will try to get these wires switched by tonight so I can let you guys know the results. Fingers crossed.
 
Ricktalife said:
Just got off the phone with AEM, and it looks like swirlfx was on the right track. They told me to disconnect the MAG output negative (MagO-) wire and leave it disconnected so the FIC reads it but does not intercept the ECU signal. Then I was told to take the MAG output positive (MagO+) wire and switch it from a intercept to a tap connection (3 way connect, 2 ends of the ECU wire and 1 FIC wire). Now that I think about it, the MAF wire really shouldn't be doing anything to affect the ECU even with a resistor wired in. The only way it would alter the signal is if I were to change the map in the software, but for now it is all 0's and I have the mode set to percent so it is altering the MAF signal by 0% across the board which does nothing.

I will try to get these wires switched by tonight so I can let you guys know the results. Fingers crossed.
Click to expand...

Ok what you've just wrote makes no sense. Which MAG? The crank mag or the cam mag or both. Either way, all MAGO wires go out to the ECU, they do not read signals. Tapping a signal with an output makes no sense. You can supply additional current as in the case of the O2 sensor, but you can't retard timing that way. If you simply tap the cam signals, you will not be able to retard timing which is the hole point in going this route instead of the SSAFC.

In any case, leaving a wire to the ECU dangling like Swirl had makes absolutely no sense.

I've read on the AEM forums that the FIC has trouble reproducing crank and cam signals with some cars. This could be an issue as well. I did drive my car around though, so I think we are ok as the car isn't going to run at all if the cam or crank signals are messed up. Would be nice to know what code I threw though.
 
Sorry I meant the Crank MAG wires. Yea I don't really understand it either but that's what the guy told me. Though as you could assume, it didn't work... I am so ****** pissed off at the lack of help you find from AEM. I'm gonna call them again and they better give me a god damn straight answer.
 
Dam it seems like everyone is having trouble with this FIC. But i have it installed and my car runs great. Like i said before i didnt do the install. Ill see if i can get some free time this week and write up a diagram of the way mine is set up. Hopefully that would help out.
 
Ok I called them again and now they are telling me there are a couple ways to wire it up depending on the car... but I asked which is more common and they told me to try this:

MagI+ intercept to sensor (wire 22)
MagI- tap wire 21
MagO+ intercept to ECU (wire 22)
Mag0- leave disconnected? (still confused about that..)

Seems pretty similar to the hall style setup, but whatever. I don't see where the MagO- wire can really go, so I suppose it is just supposed to be disconnected on this type of setup. The guy from AEM told me that some ECU's don't like the negative output and it can throw them off, so I suppose I will try leaving it disconnected and see what happens. If that doesn't work I could try tapping it into ECU pin 21 along with the MagI- wire, but something tells me that won't work. I can't mess with it anymore tonight and I'm busy tomorrow night so it may be a couple days before I can hook these up unless I use my lunch break tomorrow.
 
Mazdap5_T said:
Dam it seems like everyone is having trouble with this FIC. But i have it installed and my car runs great. Like i said before i didnt do the install. Ill see if i can get some free time this week and write up a diagram of the way mine is set up. Hopefully that would help out.
Click to expand...

That would be great, but in the mean time does my last post sound similar to what yours looks like? If you can check your crank sensor wires and tell me how they are hooked up I will take care of the diagram.
 
Ricktalife said:
That would be great, but in the mean time does my last post sound similar to what yours looks like? If you can check your crank sensor wires and tell me how they are hooked up I will take care of the diagram.
Click to expand...


I honeslty couldnt tell you. And my car is stored at a friends house atm and i cant get there right now. Ill see if i can go by sometime before the end of the week. Thats the best i can do for now
 
That would really help out Mazdap5_T. As soon as you can get to it that would be great.

Yeah, if you just tap the negative signal with the MAGI-, then you can leave the output (MAGO-) dangling.

This is probably fine, and you'll just lose some of the timing retard ability since you can only adjust the positive half of the differential signal. I still don't understand why they need to alter both the crank and cam signals to retard timing. Seems like you would simply need to alter one and keep the other the same.

This is exactly what I plan on doing with the MAFO+, just let it hang, since our ECU is never going to like it anyway, and hook the ECU straight to the MAF signal.

I do think the fuel trim should be based on MAF though, not TPS, and will probably play with the resistor values to get it more in line.
 
Seems like if you have it wired up right, you will love it.............but you have to wire it up right first!
 
Well I already massacred my wiring harness... I really don't want to rip this thing out once it is finally in.
 
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