AEM F/IC writeup

Yeah I think Rick and I are stuck with our purchases. We'll have to sell it on ebay if it comes to that, or just find someone on the forums that has more experience with piggy backs. The patch harness I have is still good for any piggy back or monitoring system though, so shouldn't have a hard time selling that.

I didn't have time to make any progress last night but I did buy a new multimeter and a code scanner. I measured the MAF output right at the MAF and it was 1.6V with the ignition on, car off, 1.9V at idle, and got up to 2.5 with my wife tapping the gas pedal in neutral.

This is right in line with what is in my log file, so the resistor is not a voltage divider (the resistance between the MAF and PCM is essentially zero). However, what it has to be doing just by defintion of Ohm's law is drawing 1.2Kohm x ~1-5V or a couple milliamps of current. I must have just not got my leads in well enough to read that small of current. The AEM must need some current to detect the voltage. I should log the AEM without the resistor and I bet I'll see 0v.

Tonight, I think I'll just convert the MAF signal to a tap, and probably put the resistor on the O2 signal per the main AEM instructions. Not sure why Swirl chose to ignore this part of the instructions but it is very explicit in the main instructions and also clearly labeled in the miata wiring diagram, so I don't think it's something we should leave out.

Also I was reading the notes on the datasheet on the SplitSecond PSC1-001 (which is what everyone calls the AFC). It is a signal modifier that is a 5V device as well, and in the case of the MSP, it is used to modify the MAF signal. However, they would have the same 5V limit that I ran into, yet plenty of people running strong with it.

I need to read up on the SS install and take a look at those maps. Could give me some insight in what is going on here.
 
Yea I had the SS AFC before this, but I did not perform the installation. I can't recall off the top of my head which wires were intercepted and which were tapped, but something tells me the MAF wire was only tapped along with the 02 wire. Once I change the crank sensor wires once again, if the car still doesn't run then I will check my MAF and 02 wire. Probably the easiest thing to do with that would be to put it back to the stock connection and go from there.
 
I wish I would have logged the exact wires and pins I used when I turbo'd and installed this into a friends MP3.
from what I remember the resistor is to help set the idle. I used a 1k and a 220 ohm to get just over the 1.2k
and it worked great. the car runs fine with no dead spots, slow to spool but pulls hard when it gets going. set at
15psi right now. If needed I can try and dig up my papers and info I used. I have one sitting here for my MSP
too but that wont go on till just before spring since it's put away for winter.
 
OK reading through the SSAFC install notes, threads etc. It appears that the SSAFC, is actually a PSC1-020, specifically for the MSP. I can't find the exact specs on it on their site, but they have others that are capable of higher voltage outputs. I am guessing the SSAFC can handle 9v. Not sure what the max of our MAF is, but scaling from my readings, I am guessing 9v is good for about 350hp or so.

The SSAFC also completely intercepts the O2 reading unlike the read/output of the AEM, which seems like the better way to go, than this tapped output method AEM uses.

The AEM is a WAY more capable unit, but its MAF input and output are not setup for our cars. I doubt anyone who has this unit working on an MSP has the MAF output going to the PCM, and hopefully MazdaP5_T can verify that for us.

Here is a thread I found with some info on a particular boosted miata setup. He didn't hook up the MAF at all. Looks like getting the O2 to work correctly will be fun as well. All sorts of resistors appear to have been used. Maybe MazdaP5_T can let us know what he used. I am thinking you just need enough resistance that when the AEM switches to send mode the current goes to the PCM and not back to the O2 sensor.

http://forum.aempower.com/forum/index.php/topic,26583.msg137862.html#msg137862
 
speedracer said:
I wish I would have logged the exact wires and pins I used when I turbo'd and installed this into a friends MP3.
from what I remember the resistor is to help set the idle. I used a 1k and a 220 ohm to get just over the 1.2k
and it worked great. the car runs fine with no dead spots, slow to spool but pulls hard when it gets going. set at
15psi right now. If needed I can try and dig up my papers and info I used. I have one sitting here for my MSP
too but that wont go on till just before spring since it's put away for winter.
Click to expand...

Do you remember putting a resistor between the O2 sensor and the AEM tap point on pin 60? All the instructions say to do this, but Swirl did not put one there.

Yes the 1.2k ohm originally worked fine, mainly because I think the car was cold and it was not using the O2 signal. Once the car warmed up it through a code and stalled after a while.

Also, you would have run into the 5V clamp problem. I guess you could have set it to 5.87V, but it still would have hit it's limit pretty early in the RPM range at 15psi.
 
I went in to the maf settings on the FIC and set it to what ever it told me to. the only stalling issue I had was when we were VTA from the BOV.
so I relocated the maf and that took care of that problem. he has no fuel cut yet.
 
Thanks for the input speedracer. I bought a pack of 220 ohm resistors that I was hoping I could use just wasn't sure if the extra 20 would make a difference. So the question that remains is whether we are supposed to put a resistor on the MAF wire or the 02 wire, and also if we should intercept the MAF wire instead of tapping it or maybe we shouldn't touch that wire at all. I haven't had any time to continue working on the crank sensor wires, and the bad weather isn't helping the matter.

I will start making an updated wiring diagram so I can piece together this rather confusing thread I have made lol.
 
ok this is what I found originally sent to me by twistiert:
get a 1.2kohm 1/2 watt resistor and put it between the maf 14b wire and power ground
4a wire l l
l l
l--resistor--l
l l
l l
4a 14b
I have wrote down that you use the 4A wire ( power ground )from the FIC and bridge it with the resistor to the 14B (maf wire)
if I remember right you only tap into them dont cut them.
 
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Well that's interesting, I don't think I ever would have figured that out lol thank you. I started the revised diagram in an excel spreadsheet so once I get the car to start and idle smoothly I will finish it up and post it on the first page. I will jot down your instructions.

edit: ok question.. if I read your description correctly I will be using the 14b MAF wire from the FIC and bridging it with a resistor to the 4a power ground wire. you said to do a tap connection, so I assume you mean to have the MAF wire from the ECU uncut. that is all good with me but what am I supposed to do with the 15b MAF signal output wire? the AEM instructions say that 14b and 15b are supposed to intercept the MAF wire, but if I do what you suggest then the 15b wire will be left disconnected.

edit edit: nevermind I misread your instructions, but I just want to clarify... I leave the 4a wire connected as per AEM's instructions, and tap into it with the resistor which will be connected to the 14b wire, so I will basically have a T looking setup correct?
 
Last edited:
Hey guys idk if this helps but I also tried to get my MAF to work with that 1.2 res and it did squat so I went back to my original configuration which runs off of the MAP for ignition, o2, and MAF. Just put MAP as the load input and as far as I know that's what it uses to manipulate each of those signals. I also don't have the MAF running through the FIC with that. I just wanted to see if I could get the MAF to work with it is why I tried the resistor.
 
I would have to double check but I'm sure you connect 4A and 14B just like the AEM wire diagrams say but then you bridge the two with
the resistors. ( 4A pwr gnd to ECU pin 77 ) --resistors-- ( 14B maf in + to ECU pin 88 )
hope this helps clear things up a bit
 
Okay that makes a lot more sense why you referred to it as a bridge haha.. I was totally lost for a bit, but assuming it works that sounds like a simple fix.
 
Don't disappoint me Ricktalife!

Im not going to even try to decipher what you girls are talking about. Ill just stay in the background and splurt out random posts that really don't make any sense ;-)
 
HighSpeed said:
Don't disappoint me Ricktalife!

Im not going to even try to decipher what you girls are talking about. Ill just stay in the background and splurt out random posts that really don't make any sense ;-)
Click to expand...

Sorry dude! That job is taken.
 
OK guys, I made a lot of headway tonight.

Ricktalife, did you never look at the mazda wiring diagram? You have to start from this thread to get anywhere.
http://forum.aempower.com/forum/index.php/topic,20181.0.html

Notice they say with a 1kohm resistor you need to adjust MAF values +15% to run stock.
I think Twistiert/Swirl etc used a higher resistor to reduce the pull down on the voltage so they would be closer to stock without adjustment.

Let me try to explain why. First thing I did was try the bypass with the resistor removed and the car ran fine. So all my wires are hooked up correctly. If you haven't gotten this far, this is where you want to start. Then I tapped the MAF signals with my multimeter and put it in my lap and drove around. The MAF voltage is nowhere near linear, there is a look up table in the PCM for sure. At WOT, it hits 4.0 volts just past 3k rpms. Now remember, I have intake, WGA, and SMIC, so this could be a little higher than stock, but I peaked out at 4.6V around 6k rpms.

So mystery solved, our MAF is 0-5V just like you would expect from a MAF. Now the crazy thing. I hook the AEM back up without the resistor, and it immediately dies. With just the ignition on though I am looking at the readings in the AEM software and it's got 5.96 in, 5.87 out, both peaked, so I measure with the multimeter and it's 8.24V again. I wasn't insane the other night. Here is why.

MAFs work by heating up a wire and measuring the resistance across the wire. The more air that flows across it, the more it will cool down and the lower its resistance will be. In a Mazda MAF, 12V is provided to the MAF and the output is a tap of a voltage divider (if you haven't looked up voltage divider please do so now). A known resistance on the ground side and the hot wire on the voltage side. With no air moving the wire is about 12% of the known resitance, creating 1.47V. When air starts flowing the resistance decreases and the voltage drop across the wire decreases. The nice thing about this is I am willing to bet our MAF is capable of sending higher than 5V if you had some serious horsepower.

A Honda on the other hand, has a 5V source. The colder the wire gets, the closer to 5V the AEM will see, but it will never go over.

Now for the tricky part, some of that "known resistance" required for that voltage divider is actually in our PCM. I pulled out the PCM and literally measured the resistance across pins 88 and 77 (103/76/51/24 also work), and sure as s*** it's 1016 Ohms. I even turned on the ignition without the PCM in the car, and as expected, without that 1016 Ohms, the ratio is no longer 12% but more like 67%, and you get 8.07 volts.

This is why AEM says to use a 1kOhm resistor but you have to adjust the MAF values to have a good baseline. Not sure how twistiert and swirl came up with 1.22kohm, but that's too high. You want to match the PCM exactly. Also 15% as the Miata guys said is too high as well, but they probably just wanted to error on the rich side, or maybe their PCM is slightly different. In fact, maybe it differs from car to car a little bit, but to know exactly, just measure across the two pins. Piece of cake.

The reason I got fuel cut is because, 1.22kohm is way to high so I hit 5v way too early. I was clamped at 5V but our PCM will cut out at 5V on the dot. And fuel cut is a terrible misnomer. It is spark cut. Fuel cut was back when we had distributors and couldn't shut off the ignition. If you look at my logs from Sunday, I was dumping tons of fuel in, and as soon as I hit 5V, it actually spiked up to 130%. Gas was probably dripping out my exhaust pipe, but since it was cold, no backfire.

So tomorrow I will go buy the correct resistors to match, but really you could just tap the MAF IN and leave the MAF OUT disconnected and all would be fine. Altering the MAF is the cheap SSAFC way to tune. We have control over the injectors themselves which is much more powerful. What it does is allow us to clamp the MAF voltage if we want to make big horsepower and not trip the PCM cut. The SSAFC can clamp the MAF voltage too I assume, but then what? They can't control the injectors, so the only way to get more power is to put in bigger injectors and reduce the MAF signal. Our injectors may tap out around the same time our MAF hits 5V, so maybe it's a moot point, but more is better than less.

Well it took all night but my understanding took a few big leaps tonight. I know it's really hard to follow, and I'll try to make legit spreadsheets and diagrams when I have time to help everyone out.
 
Last edited:
jdwk said:
OK guys, I made a lot of headway tonight.

Ricktalife, did you never look at the mazda wiring diagram? You have to start from this thread to get anywhere.
http://forum.aempower.com/forum/index.php/topic,20181.0.html

Notice they say with a 1kohm resistor you need to adjust MAF values +15% to run stock.
I think Twistiert/Swirl etc used a higher resistor to reduce the pull down on the voltage so they would be closer to stock without adjustment.

Let me try to explain why. First thing I did was try the bypass with the resistor removed and the car ran fine. So all my wires are hooked up correctly. If you haven't gotten this far, this is where you want to start. Then I tapped the MAF signals with my multimeter and put it in my lap and drove around. The MAF voltage is nowhere near linear, there is a look up table in the PCM for sure. At WOT, it hits 4.0 volts just past 3k rpms. Now remember, I have intake, WGA, and SMIC, so this could be a little higher than stock, but I peaked out at 4.6V around 6k rpms.

So mystery solved, our MAF is 0-5V just like you would expect from a MAF. Now the crazy thing. I hook the AEM back up without the resistor, and it immediately dies. With just the ignition on though I am looking at the readings in the AEM software and it's got 5.96 in, 5.87 out, both peaked, so I measure with the multimeter and it's 8.24V again. I wasn't insane the other night. Here is why.

MAFs work by heating up a wire and measuring the resistance across the wire. The more air that flows across it, the more it will cool down and the lower its resistance will be. In a Mazda MAF, 12V is provided to the MAF and the output is a tap of a voltage divider (if you haven't looked up voltage divider please do so now). A known resistance on the ground side and the hot wire on the voltage side. With no air moving the wire is about 12% of the known resitance, creating 1.47V. When air starts flowing the resistance decreases and the voltage drop across the wire decreases. The nice thing about this is I am willing to bet our MAF is capable of sending higher than 5V if you had some serious horsepower.

A Honda on the other hand, has a 5V source. The colder the wire gets, the closer to 5V the AEM will see, but it will never go over.

Now for the tricky part, some of that "known resistance" required for that voltage divider is actually in our PCM. I pulled out the PCM and literally measured the resistance across pins 88 and 77 (103/76/51/24 also work), and sure as s*** it's 1016 Ohms. I even turned on the ignition without the PCM in the car, and as expected, without that 1016 Ohms, the ratio is no longer 12% but more like 67%, and you get 8.07 volts.

This is why AEM says to use a 1kOhm resistor but you have to adjust the MAF values to have a good baseline. Not sure how twistiert and swirl came up with 1.22kohm, but that's too high. You want to match the PCM exactly. Also 15% as the Miata guys said is too high as well, but they probably just wanted to error on the rich side, or maybe their PCM is slightly different. In fact, maybe it differs from car to car a little bit, but to know exactly, just measure across the two pins. Piece of cake.

The reason I got fuel cut is because, 1.22kohm is way to high so I hit 5v way too early. I was clamped at 5V but our PCM will cut out at 5V on the dot. And fuel cut is a terrible misnomer. It is spark cut. Fuel cut was back when we had distributors and couldn't shut off the ignition. If you look at my logs from Sunday, I was dumping tons of fuel in, and as soon as I hit 5V, it actually spiked up to 130%. Gas was probably dripping out my exhaust pipe, but since it was cold, no backfire.

So tomorrow I will go buy the correct resistors to match, but really you could just tap the MAF IN and leave the MAF OUT disconnected and all would be fine. Altering the MAF is the cheap SSAFC way to tune. We have control over the injectors themselves which is much more powerful. What it does is allow us to clamp the MAF voltage if we want to make big horsepower and not trip the PCM cut. The SSAFC can clamp the MAF voltage too I assume, but then what? They can't control the injectors, so the only way to get more power is to put in bigger injectors and reduce the MAF signal. Our injectors may tap out around the same time our MAF hits 5V, so maybe it's a moot point, but more is better than less.

Well it took all night but my understanding took a few big leaps tonight. I know it's really hard to follow, and I'll try to make legit spreadsheets and diagrams when I have time to help everyone out.
Click to expand...

English Please! I think I read something about a flux capacitor or something

J/K, I am starting to understand what is going on here. We may need a new "how-to" with specific instructions......that is of course, everything works according to your theory. Thanks for taking one for the team.
 
Nice dude! I think you explained everything very well, cause I understand it and I'm no electrician haha. Those are some interesting facts you mentioned about our MAF and are very good to know. I was planning on tuning with the injectors as well, but since I already bought a shitload of resistors I will just use a 1k and a 100 to get 1.1k which is about as close as we can get without tuning I imagine. So here's my list of corrections to make:

MAGI - changes to tap
MAGI + changes to intercept sensor
MAGO + changes to intercept ECU
MAGO - leave disconnected

Add 1.1k resistor to bridge MAF IN + and PWR GND (tap both ends)
Reconnect MAF wire
MAF IN + changes to tap
Disconnect MAF OUT +

If any of my notes seem wrong please let me know. I will be starting on this as soon as I get some free time.
 
HighSpeed said:
English Please! I think I read something about a flux capacitor or something

J/K, I am starting to understand what is going on here. We may need a new "how-to" with specific instructions......that is of course, everything works according to your theory. Thanks for taking one for the team.
Click to expand...

Lol flux capacitor... never gets old. I agree a "how-to" with pictures would definitely help other members translate this mess, and we could just link this thread to it and vice versa. No worries though, we will conquer this s***. Just need to be patient, and not lose our tempers lol. Again many thanks to jdwk for the detailed explanation of his findings.
 
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