justanothermp5
Banned
- :
- Rust Bucket
im not even following this thread regularly, and that guys post made a ton of sense
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AEM F/IC writeup
- Thread starter Ricktalife
- Start date
im not even following this thread regularly, and that guys post made a ton of sense
Nah, I was just keeping this thread slightly on the light side. I follow what he is saying but I need to see what he is talking about as well.
Yeah I know its really hard to follow without diagrams. I'll try to scan some in at work tomorrow.
So rather than try to make some exact resistor I just bought a .1 to 1k potentiometer at rapeyou shack, I mean radio shack. I put it in series with a 470 ohm and set it to 1016 ohm exactly.
I put the bridge in as per the Miata wiring diagram (same as swirl), hooked the wiring harness up to the AEM and measured 1.47 V with the ignition on, exactly what I measured directly from the MAF with only the stock PCM hooked up. Perfect.
However, I open up the gauges and see the AEM is reading 1.32 V, not 1.47 V. So the AEM has a little bit of load itself or is simply calibrated differently than my multimeter. I saw the same ~10% discrepency when I logged the MAF signal on the analog input last night.
I decide to see if 1.32 V according to the AEM is the same as 1.47 V to the PCM, and it's definitely not. The car starts but immediately dies, in hindsight I should have just measured the MAFO+ signal. Instead, with just the ignition on, I adjusted the potentiometer until the "Maf in" read 1.47 V in the AEM software. I then start the car, and it idles and then drives nearly normal. If I was at a red light long enough the RPMs would drop to 500 and the car would almost stall before revving back up, but overall it seemed ok. I didn't peg it since I don't have the wideband hooked up and don't completely trust this resistor setup, but I decided this is at least a good starting point to tune and started putting the LC1 in.
I got the cables in through the gromet (by the way a utility knife works way better than a drill), but was too tired to start soldering again in the footwell.
If you want to intercept the MAF signal the pot is definitely the way to go. I am not even sure what resistance it's set at now, but what you need to do is measure the voltage of your MAF when it is hooked up only to the PCM. Then, hook it up to the AEM and adjust your resistance to ground until the AEM outputs the same voltage. Do this roughly in the same time period as that voltage will change with temperature and barometric pressure. Also the AEM doesn't output exaclty what it says it does, probably because it's not expecting that 1016 ohm resistance in the PCM and the resulting load.
For reference, I just measured voltage directly at the MAF, 1.56V, while the AEM said Maf in and out was 1.49 V, yet I measured 1.43V on the output.
This should get you to the same point as me, whether or not you understand my voltage divider and Honda vs Mazda theory. As for the other wires, I did put a 1k ohm on the O2 sensor wire. But I did not disconnect any other connections. I am intercepting all four cam and crank signals as per the AEM instructions.
The unfortunate thing about this, not counting the 4 day headache, is since we'll all have slightly different resistance values, we won't be able to share maps. If we can get all our MAFO+ signals to match our stock MAF readings, then we should be be pretty close, but it's not exactly a straightforward procedure. In fact, I would recommend anyone not familiar with a potentiometer, just tapping the MAF, and you'll be good up until you max out the PCM.
So rather than try to make some exact resistor I just bought a .1 to 1k potentiometer at rapeyou shack, I mean radio shack. I put it in series with a 470 ohm and set it to 1016 ohm exactly.
I put the bridge in as per the Miata wiring diagram (same as swirl), hooked the wiring harness up to the AEM and measured 1.47 V with the ignition on, exactly what I measured directly from the MAF with only the stock PCM hooked up. Perfect.
However, I open up the gauges and see the AEM is reading 1.32 V, not 1.47 V. So the AEM has a little bit of load itself or is simply calibrated differently than my multimeter. I saw the same ~10% discrepency when I logged the MAF signal on the analog input last night.
I decide to see if 1.32 V according to the AEM is the same as 1.47 V to the PCM, and it's definitely not. The car starts but immediately dies, in hindsight I should have just measured the MAFO+ signal. Instead, with just the ignition on, I adjusted the potentiometer until the "Maf in" read 1.47 V in the AEM software. I then start the car, and it idles and then drives nearly normal. If I was at a red light long enough the RPMs would drop to 500 and the car would almost stall before revving back up, but overall it seemed ok. I didn't peg it since I don't have the wideband hooked up and don't completely trust this resistor setup, but I decided this is at least a good starting point to tune and started putting the LC1 in.
I got the cables in through the gromet (by the way a utility knife works way better than a drill), but was too tired to start soldering again in the footwell.
If you want to intercept the MAF signal the pot is definitely the way to go. I am not even sure what resistance it's set at now, but what you need to do is measure the voltage of your MAF when it is hooked up only to the PCM. Then, hook it up to the AEM and adjust your resistance to ground until the AEM outputs the same voltage. Do this roughly in the same time period as that voltage will change with temperature and barometric pressure. Also the AEM doesn't output exaclty what it says it does, probably because it's not expecting that 1016 ohm resistance in the PCM and the resulting load.
For reference, I just measured voltage directly at the MAF, 1.56V, while the AEM said Maf in and out was 1.49 V, yet I measured 1.43V on the output.
This should get you to the same point as me, whether or not you understand my voltage divider and Honda vs Mazda theory. As for the other wires, I did put a 1k ohm on the O2 sensor wire. But I did not disconnect any other connections. I am intercepting all four cam and crank signals as per the AEM instructions.
The unfortunate thing about this, not counting the 4 day headache, is since we'll all have slightly different resistance values, we won't be able to share maps. If we can get all our MAFO+ signals to match our stock MAF readings, then we should be be pretty close, but it's not exactly a straightforward procedure. In fact, I would recommend anyone not familiar with a potentiometer, just tapping the MAF, and you'll be good up until you max out the PCM.
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Ricktalife
Member
- :
- 2012 Subaru WRX
So intercepting both crank sensor wires didn't give you any problems? I did that already and the car still died on me, so it must be the MAF wire that's ******* s*** up. I'm thinking I will just reconnect the MAF wire back to stock at least for now. I mean, do we really need the MAF signal for anything unless we are tuning via the MAF voltage map? We already know that's not an effective way to tune anyhow.
Yes, if you haven't tried getting the car to work without the MAF wire hooked up at all (straight to PCM, no tap), then that's where you need to start.
No you don't really need the MAF, as you probably read from the turbo Miata thread, his MAF signal was not hooked to the AEM at all.
If you are just tapping the MAF, I would still be careful of the input impedance on the AEM. When I was running around with just the MAF signal tapped, it was idling a little rough. I pulled the tap and it smoothed out. This might be why the Miata guy didn't even tap his. I unfortunately didn't have a good look at the multimeter when I pulled the tap. This is also why I had to adjust the my pot a little higher than 1016 ohms. I'll try to measure the resistance across it now.
The reason I am intent on using the MAF feature, is because I live in AZ, and temperatures will reach 120 degrees in the summer. The AEM does not have an IAT sensor like the car does, so I have to infer the temperature by the MAP and MAF reading. If my MAP is high and my MAF is low, then my IAT is high, and I need to run richer to prevent knock, or pull timing. In colder weather like now, I can get away with running leaner.
Unfortunately, the ignition map is 2D, and I can only choose MAF or MAP, not both. I wonder if I can convince AEM to put that in a firmware update.
No you don't really need the MAF, as you probably read from the turbo Miata thread, his MAF signal was not hooked to the AEM at all.
If you are just tapping the MAF, I would still be careful of the input impedance on the AEM. When I was running around with just the MAF signal tapped, it was idling a little rough. I pulled the tap and it smoothed out. This might be why the Miata guy didn't even tap his. I unfortunately didn't have a good look at the multimeter when I pulled the tap. This is also why I had to adjust the my pot a little higher than 1016 ohms. I'll try to measure the resistance across it now.
The reason I am intent on using the MAF feature, is because I live in AZ, and temperatures will reach 120 degrees in the summer. The AEM does not have an IAT sensor like the car does, so I have to infer the temperature by the MAP and MAF reading. If my MAP is high and my MAF is low, then my IAT is high, and I need to run richer to prevent knock, or pull timing. In colder weather like now, I can get away with running leaner.
Unfortunately, the ignition map is 2D, and I can only choose MAF or MAP, not both. I wonder if I can convince AEM to put that in a firmware update.
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Also if you want to try this pot trick out. The reason you can't just stick in any resistor and scale with the AEM is because the relationship is not linear. The resistance of the MAF wire changes with the voltage output, so it's a second degree equation. (aka a parabola, as in the percent difference from stock is much less as the resistance of the MAF wire decreases). And I would type it in here, but it doesn't simplify into anything that is typable. I could give you an excel sheet you could use that formula to fill out you MAF table for a given resistance value. That 15% crap from the AEM forums might get it to run, but it will be more and more rich the higher the maf signal. But it is best to just get a potentiometer and get it exact.
On the output however, there apparently is some output impedence, and a long with the 1016 ohms of the PCM, we have ourselves another voltage divder. Thankfully, the output impedence of the AEM and input impedence of the PCM should be fairly static, and so that small voltage drop should be linear. It means for us to run perfectly stock, we will have to adjust the values +4%. So unfortunately, a zero baseline map is not possible using the MAF out.
By my math, I am currently running 4% too lean, which in our cars, is probably a good thing. I'll wait until I get the wideband hooked up before I put my money where my mouth is though.
As a side note, a very crappy riced out Neon was trying to egg me on while I was data logging last night. "Not yet buddy, not yet."
On the output however, there apparently is some output impedence, and a long with the 1016 ohms of the PCM, we have ourselves another voltage divder. Thankfully, the output impedence of the AEM and input impedence of the PCM should be fairly static, and so that small voltage drop should be linear. It means for us to run perfectly stock, we will have to adjust the values +4%. So unfortunately, a zero baseline map is not possible using the MAF out.
By my math, I am currently running 4% too lean, which in our cars, is probably a good thing. I'll wait until I get the wideband hooked up before I put my money where my mouth is though.
As a side note, a very crappy riced out Neon was trying to egg me on while I was data logging last night. "Not yet buddy, not yet."
Ricktalife
Member
- :
- 2012 Subaru WRX
Ok that makes sense why you would use the MAF, but yea I think that has been the heart of my problem so it is going back to stock. I plan to work on it tonight so hopefully it will be ready to reassemble by the end of the night. My car needs cleaned out BAD.
I will adjust my wiring diagram based on your results.
I will adjust my wiring diagram based on your results.
Ricktalife
Member
- :
- 2012 Subaru WRX
Ok I posted my 'nearly complete' wiring diagram. I will convert it to a photo once it is finished so you don't have to download to view it. Please let me know if there are any mistakes.
719prottege
Member
- :
- 03 msp
so is it all hooked up well now?
Ricktalife
Member
- :
- 2012 Subaru WRX
so is it all hooked up well now?
As a matter of fact, YES! Lol I just took it for a test drive after switching the MAF wire back to stock and the crank sensor wires back to intercept. It was that bloody MAF wire that was causing all the problem I don't know why I didn't just put it back to stock in the first place. I will work on finishing the diagram for you guys. Can't wait to get a base tune so I can have my turbo back with no fuel cut.
719prottege
Member
- :
- 03 msp
saweeeeet!!!! now i can order mine! haha good thread man!
guess i will pick mine up today.
You suck..........
Let me know if you have issues. I really hope this will get me to my goals
justanothermp5
Banned
- :
- Rust Bucket
Nah, I was just keeping this thread slightly on the light side. I follow what he is saying but I need to see what he is talking about as well.
that wasnt directed towards you lol i was just saying in general
Ricktalife
Member
- :
- 2012 Subaru WRX
So what are the draw backs from not intercepting the MAF wire to tune? Will you just be tuning with MAP?
Yea that's about it. The MAF signal is just one way of tuning the FIC, and considering you need to use resistors just to make it work, it is obviously not the optimal solution. Instead I am tuning with the FIC's onboard MAP sensor which measures in atmospheric pressure, referred to as PSIA. This is much more effective than just measuring PSI like the SSAFC users do, because as you can assume it takes the atmospheric pressure wherever you are located and applies it to your fuel map so you can easily tune it to your city's elevation.
So for example, if the atmospheric pressure in my city/county/whatever is 15.0 and I am boosting a solid 10 psi, then the PSIA on my fuel map would go up to at least 25psia because the formula is just simple addition. PSIA = P(atmospheric) + P(boost). The AEM instruction manual posted on page 1 explains this concept.
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