94-95 & 96-97 MAF Delete Discussion - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-20-2007, 01:13 PM   #21
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Quote:
Originally Posted by Braineack View Post
ODBI will still get a CEL without a AIT signal.
Sure, if you kept your stock ecu to trigger a CEL.

Standalone MS ftw!
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Old 11-20-2007, 02:13 PM   #22
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Originally Posted by whaaamx5 View Post
sam, according to diy installation thats why i did pins 3&4 for the IAT
http://megasquirtpnp.com/models/mm94...495_manual.htm
look half way down the page...
You use pins 3 and 4 because the MSPNP is wired to use those pins as input for the GM AIT sensor.
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Old 11-20-2007, 02:37 PM   #23
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use you pins 3 & 4 because 3 is the sensor ground, and 4 is the output to the ECU. So should build your harness to pick up the AIT sensor signal off the factory harness. Make wiring extremely simple/easy....
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Old 11-20-2007, 02:50 PM   #24
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OK, im a little less confeused now
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Old 11-20-2007, 03:54 PM   #25
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Originally Posted by whaaamx5 View Post
OK, im a little less confeused now
I'm not... I think I need a diagram.

The problem I see here is that there is only one signal line (4).

1) Chassis Ground (SHARED)

2) Sensor Ground (SHARED)

3) 5V (SHARED)

4) Red/Wh = Signal

5) 12V (SHARED)

So, the ecu can't measure resistance/current change on the heater or it can't measure AIT. Unless both signals are being kicked out on the same line, like say in a PWM. This is the issue I'm having. The ONLY line not shared (per the schematic) is pin 4. One wire = one signal. WTF?
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Old 11-20-2007, 04:26 PM   #26
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beats me
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Old 11-20-2007, 04:35 PM   #27
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#3 is the intake sensor....it shouldn't be a shared signal. it's simply the input for the ECU to read the AIT from.

Take voltmeter from the #3 pin on the harness and (94-95 2P Red/Black) (96-97 3K Red/Black) and you'll have no resistance. it goes straight from the harness to the ECU.

Since the MAF only has two functions, temp and airflow, you can easily assume the red/green wire is the MAF signal. Black/Blue & Black/Lt Green are always grounds, all years. White/Red is always +12v, all years.

Last edited by Braineack; 11-20-2007 at 08:13 PM.
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Old 11-20-2007, 05:24 PM   #28
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Originally Posted by reddroptop View Post
Sure, if you kept your stock ecu to trigger a CEL.
I did, to control A/C & Idle.... and I don't get a CEL. I don't get it but Meh!
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Old 11-20-2007, 06:28 PM   #29
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Quote:
Originally Posted by Braineack View Post
#4 is the intake sensor....it shouldn't be a shared signal. it's simply the input for the ECU to read the AIT from.

Take voltmeter from the #4 pin on the harness and (94-95 2P Red/Black) (96-97 3K Red/Black) and you'll have no resistance. it goes straight from the harness to the ECU.

Since the MAF only has two functions, temp and airflow, you can easily assume the red/green wire is the MAF signal. Black/Blue & Black/Lt Green are always grounds, all years. White/Red is always +12v, all years.
My bad... pin 3 isn't a shared 5V. So pin 3 through a resistor to ground should deal with one function... pin 4 through a resistor to 12V should provide the second?
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Old 11-20-2007, 08:12 PM   #30
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well, you'd be smart to wire your GM AIT sensor directly through the MAF harness....that way you kill two birds with one stone, the ecc sees it and is happy and MS sees it and is happy.

the MAF signal is a guess, but an educated guess. I assume as long as the ecu sees something between 0-5v it won't throw a code.
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Old 11-20-2007, 08:37 PM   #31
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Quote:
Originally Posted by Braineack View Post
well, you'd be smart to wire your GM AIT sensor directly through the MAF harness....that way you kill two birds with one stone, the ecc sees it and is happy and MS sees it and is happy.

the MAF signal is a guess, but an educated guess. I assume as long as the ecu sees something between 0-5v it won't throw a code.
Problem being that my AIT is already wired in on an independent wire and the bung has already been welded to the cold side pipe right next to the TB. I really don't want to re-wire that **** since it works atm.

why would it be any smarter to wire in the GM AIT instead of a static resistor? it's not like the stock ECU is going to know what is going on anyways since the GM and stock sensors have difference resistance curves.
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Old 11-20-2007, 08:53 PM   #32
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its just easy if you haven't already wired it. otherwise try a resistor, see if it throws a code, if it does, jump your ait wire to the stock one.
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Old 11-20-2007, 09:36 PM   #33
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Hurry up and try this out guys, I need to install my MS this weekend and need to decide what im doing so I dont have to run extra wires.
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Old 11-20-2007, 11:43 PM   #34
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I ran my AIT back through one of the wires in the A/C harness (there's 3 wires that go back to the ECU if I remember correctly). And the harness is right there next to the TB in the 94. But I don't have A/C. It made a nice alternative to running a wire across the engine bay to the MAF connector, or running a completely separate wire.

I'm running standalone, so I can't offer any wisdom on the CEL issue.

-Mike
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Old 11-21-2007, 09:55 AM   #35
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Originally Posted by Saml01 View Post
Hurry up and try this out guys, I need to install my MS this weekend and need to decide what im doing so I dont have to run extra wires.
I probably won't get this figured out this weekend. My turbo should be done tonight so I'll be tuning for the next few days. I figure I'll just unplug it and live with the CEL for now. I've got a month to figure this out before I have to get inspected
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Old 11-21-2007, 11:07 AM   #36
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Originally Posted by Arkmage View Post
I probably won't get this figured out this weekend. My turbo should be done tonight so I'll be tuning for the next few days. I figure I'll just unplug it and live with the CEL for now. I've got a month to figure this out before I have to get inspected
Fine, so then its on me. What do I have to do exactly?

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Originally Posted by Braineack View Post
its just easy if you haven't already wired it. otherwise try a resistor, see if it throws a code, if it does, jump your ait wire to the stock one.
Luckily I have two AIT sensors on my table, both GM. I think ill just take the one I wont use and plug it in, just need to know which pins to plug it into and which to jump with a resistor.
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Old 11-21-2007, 11:27 AM   #37
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Sam I'd get it running with the MAF attached and share the factory sensor. Make sure as is kosher and no CELs as is. Go ahead and get the GM sensor installed where you want it, but leave it disconnected.

then when you are confident everything is good, remove the afm and wire the sensor up into the harness, then try the resistor. Not sure what size you'd want, something to drop 12v to 4v.
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Old 11-21-2007, 12:00 PM   #38
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So where would I jump the resistor, 12volt and the signal line? That wont work.

Im guessing you want me to use the MS because the car wont run if I just plugged in the AIT without the MAF.
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Old 11-21-2007, 12:05 PM   #39
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yeah, get the MS running using the MAF.


then remove the MAF and replace it with the GM AIT. and try jumping the MAF signal with the resistor.
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Old 11-21-2007, 12:08 PM   #40
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Quote:
Originally Posted by Braineack View Post
yeah, get the MS running using the MAF.


then remove the MAF and replace it with the GM AIT. and try jumping the MAF signal with the resistor.
Dude wait.

The wiring doesnt make sense.

The AIT gets wired into 5v, and signal. Whats left? Sensor Ground, 12v, and Chassis ground. I cant wire in 12V + resistor into the Signal, I am no electrician but that doesnt sound right.

Last edited by Saml01; 11-21-2007 at 12:28 PM.
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