An alternative to a Hacked MAF

[justjuiceit]

Has anyone tried using a resistor with the MAF to compensate for larger injectors instead of hacking the MAF?

[WDRacing]

There have been a few discussions on similer idea's. I don't think it will work.

[justjuiceit]

Unless the voltage increase is not linear with the increase of airflow, I don't see why it wouldnt work. I do remember reading someplace that you would have to run it through some processing and then an amplifier. How exactly does the SAFC work?

[MikeMurphy]

juice, go read the wiring diagram on the apexi website and you will see how it works.

I dont think resistors will work at all. They alter the signal, but dont alter the duration of the signal, thus the injector pulse length will still be the same. Injectors are either open, or closed.

someone correct me if im wrong, but im pretty certain im right.

[justjuiceit]

I wouldn't see why the duration of the signal would change, because the way I thought MAFs worked was that they determined the mass of air by supplying a constant voltage supply, the more voltage applied the more mass that is flowing. If the voltage was decreased, then the computer would think there was less air flowing and would decrease the pulse length. Using a resistor to decrease the voltage by 37% would fool the computer that it was receiving that much less air, so the computer would not inject as much fuel. How much affect does the O2 sensor have?

[justjuiceit]

By the way, I was talking about putting a resistor with the MAF, and not the injectors.

[MikeMurphy]

my bad. I was thinking injectors for some reason. Im a goof .

[justjuiceit]

no problem, I looked at the wording for my question and I could see how easily you could have came up with that; I edited the question to be a bit more clear

[ziggy682]

Well, I just came upon this exact situation. My car was broken into, and my SAFC 2 was stolen. I'm running 370cc injectors, because I'm going turbo soon. So, I was in a delima, because my car wouldn't run right with the bigger injectors without anything to correct their flow.

I did some serious searching, because I thought exactly what you're thinking. That if you put a resistor inline between the MAF and the ECU that would pull voltage down 27%, the car would run right. Here's why I don't think this will work after I did research on it.

Because of the design of the circuitry in the MAF, if you place a resistor inline after it, it will not function properly. Basically, because the circuitry shouldn't be seeing any resistance, it will affect the voltage output when it does. I know this doesn't really make much sense, but my brother has been in electronics for 15 years and he was much better at explaining it too me. Although, he wasn't 100% sure it wouldn't work, because we didn't have a wiring diagram of the MAF circuitry.

Basically, the way to get it to work would be to build a circuit that reads the voltage from the MAF, then creates a new voltage source that is 27% lower. Again, I'm not very good at explaining this, but it made sense when it was explained to me.

However, there is an easier solution. To get my car to run right, we just let in air that was not metered by the MAF. Basically we just cut a hole in the intake pipe after the MAF and played with the size. I roughly tuned it with my air/fuel gauge(I know they're not that perfect, but they're better than nothing), and then put a temporary "filter" over it to keep some dust out. Believe it or not, I can't tell the difference driving my car now from driving my car with the SAFC.

I believe this is a very viable alternative to the hacked MAF setup. Obviously, my solution is just temporary, but you could find the right size hole, attatch a pipe to it, and put a breather filter over the end. WDRacing has talked about this before, and I can tell you from experience that it does work, however I am still NA, so I can't tell you how safe it is under boost.

Mike

[justjuiceit]

I would be very interested what exactly your brother proposed, since I know electrical gurus that know nothing about cars, but can whip me up what I tell them too! According to Joe Pettit, "the hot wire sensor by Bosch measures electrical current in milliamps. Current flowing through the wire heats it to a temperature that is always above the inlet air temperature by a fixed amount. Air flowing across the wire draws away some of the heat, so an increase in current flow is required for it to maintain the fixed temperature. Low current at idle and high current at WOT. The current necessary to heat the wire is proportional to the mass of air flowing across the wire. A temperature sensor in the MAS provides a correction for intake air temperature so that the output signal is not affected by it. A circuit in the MAS converts the current reading into a voltage signal for the ECM. The output of is not linear with respect to airflow; its sensitive to low air flow and less sensitive at high air flows"

[huguetpj]

To keep the electronic circuit inside the MAF as simple as possible, I'm pretty sure Nissan did not include an impedance separator at the output. Thus if you connect a resistor bridge at the output to make the ECU read less voltage you would affect the balance in the circuitry itself thus causing the MAF to malfunction. I think I saw a MAF circuit somewhere so I'm stating this of the top of my head, but I'm about 90% sure. But when dealing with any kind of sensing equipment you need and impedance separator of some kind to read the signal.

The best way to do this is how the SAFC does it. Use an amplifier/divider circuit to alter the MAF voltage signal. The circuit will have a high impedance input (as does the ECU and SAFC) so it won't affect the MAF circuit. The circuit will only need 1 IC, 2-4 resistors and 1 variable resistor (potentiometer - not sure about the translation). The variable resistor will allow you to "tune" the signal coming out. The SAFC does this electronically and can change values with revs. The simple circuit will give you a single +-% throught the rpm range.

Don't remember the code for the IC, but if you go into Jameco or Digikey and look for amplifier you'll eventually find it.

[ziggy682]

Yes, huguetpj said exactly what my brother said. Sorry I couldn't explain it better.

[:: orion ::]

Running a bypass tube is the same thing as hacking the MAF, but not as accurate (filter # 2 gets dirty, different vacuum/flow through the bypass tube as the RPMs increase, etc...).

Do a search for the old hacked MAF threads, there was a lot of discussion about different ways to do it...this has all been discussed before.

- Brian

[WDRacing]

But a bypass tube that starts at the first filter just in front of the MAF will ingest the same temp air and from the same source. Also eliminating the need for a second filter. In theory it will work exactly the same as changing the diameter of the maf itself. Simply allowing unmeasured air to enter the motor.

WD

[:: orion ::]

Agreed...but I find it easier to just slap the internals of the MAF into a 3" tube and add some fuel pressure to tune.

I'll probably run a bypass someday on my S13, just to see how it does...I can swap the fuel rail from the turbo S14. We'll see what the wideband says...hehe.

- Brian

[WDRacing]

Yeah, I'm gonna be doing some playing with mine as well. I'll let ya know how it goes.