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Old 11-01-2007, 11:44 AM   #1
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Default Removing the MAF without a CEL (ODB-II)

Heres a question. What advantage does keeping the Maf and interfacing it with the MS provide if I am still going to use the MAP for fuel calculation?

I wont be pulling my maf because of emissions reasons, so I might as well use it if it provides a benefit. This is in reference to your post mentioning removing R4 if you are retaining maf.
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Old 11-01-2007, 11:48 AM   #2
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does the MAF have anything to do with emissions?


pulling the resistors on the board is because MS shares the sensors with the ECU and it alters the reading from the bias resistance. You could leave them both in and figure it out when loading easytherm values, it's just a suggestion.

example:

I had R7 installed. My coolant temps showed 190 when the fans switched cruise when truly they come on at 210. So my temps we about 30 too low. Pulled the resistor and they come on at an indicated 210.
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Old 11-01-2007, 12:25 PM   #3
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Originally Posted by Braineack View Post
does the MAF have anything to do with emissions?


pulling the resistors on the board is because MS shares the sensors with the ECU and it alters the reading from the bias resistance. You could leave them both in and figure it out when loading easytherm values, it's just a suggestion.

example:

I had R7 installed. My coolant temps showed 190 when the fans switched cruise when truly they come on at 210. So my temps we about 30 too low. Pulled the resistor and they come on at an indicated 210.
Well if there is no MAF present I get a CEL. So its going to stay plugged in. I was wondering if I could put it to good use?

-----------------

Why do you jumper XG1 to TachSelect and not like the manual states in step 52? unless this is one of the miata specific mods?
I will have to follow the manual on this step because I am using a stim, so im curious why this has to be how you did it.


Do the miata specific modifications go in place of a step, or in conjunction to a step(s)? I would guess in place of step 65.
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Old 11-01-2007, 12:30 PM   #4
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Originally Posted by Saml01 View Post
Well if there is no MAF present I get a CEL. So its going to stay plugged in. I was wondering if I could put it to good use?

false. as long as you make sure the ecu sees some sort of resistance for the AIT circuit (IE, share the signal) then it wont throw a code.

example: http://www.youtube.com/watch?v=u_azjL8kBlQ


For the Hall sensor, optical sensor, coil negative terminal or points:

* Jumper XG1 to XG2 on the bottom side of the PCB, near the 40 pin socket,
* Jumper OPTOIN to TACHSELECT on the bottom side of the PCB, near the DB37 connector, opposite the heat sink.
* Jumper TSEL to OPTOOUT on the bottom side of the PCB, near the center.



if you follow the mega manual, it will take you x5 as logn to build. follow the pic i posted and just install the corresponding component, should only take 1-2 hours.

Last edited by Braineack; 11-01-2007 at 12:44 PM.
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Old 11-01-2007, 02:02 PM   #5
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Originally Posted by Braineack View Post
false. as long as you make sure the ecu sees some sort of resistance for the AIT circuit (IE, share the signal) then it wont throw a code.

example: http://www.youtube.com/watch?v=u_azjL8kBlQ

Ok, so you want me to share the signal from the AIT sensor with the ECU?

edit: NVM step 65 is for MS2 stuff. had to read it a few times to understand.

Last edited by Saml01; 11-01-2007 at 02:20 PM.
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Old 11-01-2007, 02:21 PM   #6
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This thread went from a how to to a FAQ in less than 1 pg....impressive?
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Old 11-01-2007, 02:26 PM   #7
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This thread went from a how to to a FAQ in less than 1 pg....impressive?
Is that a bad thing?

I am about to dig up all my threads and make a massive "BEGGINERS FAQ".
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Old 11-01-2007, 02:33 PM   #8
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Originally Posted by Saml01 View Post
Ok, so you want me to share the signal from the AIT sensor with the ECU?

yes. easiest way to do it, is wire the db37 harness directly into the AIT circuit. then wire the AIT sensor into the MAF harness itself. both the MS and ECU will share the signal and be happy, as long as you remove R7 and use the stock rx7 bias resistance value in easytherm.

you shouldn't get any check engine lights.
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Old 11-01-2007, 04:01 PM   #9
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false. as long as you make sure the ecu sees some sort of resistance for the AIT circuit (IE, share the signal) then it wont throw a code.
Braineack... your car is not OBD2 is it? I don't think this will work on the OBD2 cars as the MAF is watched by the diagnostics, and outputs a PWM rather than a linear voltage. You can trick the AIT with a resistor or by hooking it into the same AIT used for the MS, but the MAF signal is a bit more difficult to replicate. I don't think it will care if the signal changes or not, but it will be looking for a PWM or will probably throw a code for the MAF.

Codes are important where I am for passing emissions. OBD2 cars don't get sniffed, but if we have a CEL we won't pass.
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Old 11-01-2007, 04:53 PM   #10
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you are correct, i forget about odb-II issues.


a 12v source heats the sensor right? when it cools the voltage drops.

would not a simple resistor between the stock ecu and MAF harness not work? it doesn't really need to read the signal other than to know its changed. the harness will still get the +12v signal, so the only thing that's not happening is the resistance dropping. Or a just resistor from a ground to the MAF signal?
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Old 11-01-2007, 07:08 PM   #11
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Quote:
Originally Posted by Braineack View Post
you are correct, i forget about odb-II issues.


a 12v source heats the sensor right? when it cools the voltage drops.

would not a simple resistor between the stock ecu and MAF harness not work? it doesn't really need to read the signal other than to know its changed. the harness will still get the +12v signal, so the only thing that's not happening is the resistance dropping. Or a just resistor from a ground to the MAF signal?
Not quite... the ECU doesn't do the calcs for the flow rate, there is a circuit inside the MAF which calculates the mass air flow and kicks it back to the ECU as a digital PWM signal. Now, I can't prove this as yet on the miata, but it's been my experience from working with Bosch Motronic in the past. I'll update you once I have tested a few options and know what works. I'll send you all of the OBD2 compliance data once I have the turbo finished and I pass inspection with MS in parallel in January.
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Old 11-02-2007, 01:42 AM   #12
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You could always just leave the maf connected, just tuck it away in the engine bay out of sight.
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Old 11-02-2007, 10:26 AM   #13
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You could always just leave the maf connected, just tuck it away in the engine bay out of sight.
That's the backup plan... but ideally I'd like to get the clutter out of the way.

I've learned my lesson about resistors to replace heater elements. This time I'm getting a big fat *** resistor with a heat since with hounting holes to screw down in the bay... that $0.50 radio shack caught my car on fire.
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Old 11-02-2007, 11:10 AM   #14
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What about the resistor that has to come between the LC1 and the ECU? Big heatsink for that as well?
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Old 11-02-2007, 11:33 AM   #15
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Old 11-02-2007, 11:52 AM   #16
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Could you disassemble the Hotwire housing and just stick the element and related electronics into, say, your turbo inlet pipe? That would get rid of the clutter/restriction of the MAF. Or do you think the change in pipe diameter would change the signal enough to still throw a code?
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Old 11-02-2007, 12:00 PM   #17
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not sure. I'm going along the lines the the ecu won't care what the signal is, as long as it sees a signal.
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Old 11-02-2007, 12:36 PM   #18
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Could you disassemble the Hotwire housing and just stick the element and related electronics into, say, your turbo inlet pipe? That would get rid of the clutter/restriction of the MAF. Or do you think the change in pipe diameter would change the signal enough to still throw a code?
I don't understand what you mean by disassembling it. But I bet if you kept the MAF in the air intake tract after the filter it wont make the slightest difference in the amount of air flowing in to matter.

========

I still dont understand why we need a resistor coming from the LC1 to the ECU. I understand that our O2 element is heated, all the resistor does is slow the current down. How does that effect the ECU?

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For the O2?
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Old 11-02-2007, 12:47 PM   #19
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lc1 doesn't need a resistor.
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Old 11-02-2007, 01:24 PM   #20
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Originally Posted by Saml01 View Post
I don't understand what you mean by disassembling it. But I bet if you kept the MAF in the air intake tract after the filter it wont make the slightest difference in the amount of air flowing in to matter.
I'm not familiar with the MAF used in the OBDII Miatas but in my experience there are two types of Hotwire MAFs, those with a housing and those without.

The first type are a sealed unit that will attach inline with the intake tract somewhere, has all the electronics contained inside and a probe which sticks into the path of airflow. The second is just a self contained probe that will bolt to the outside of one of the intake pipes and the probe portion will protrude into the intake piping.

I assumed that if you couldn't find a use for the MAF other than preventing a code you would want to eliminate it as a source of restriction and or clean up your engine by eliminating it. If its the second type it would be easy, if the first you would have to do a bit more work by reducing it down to the components that you actually need to prevent the CEL.

As for not being a restriction, I would agree except if it is a different size than the piping you could use if it wasn't there.
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