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Old 08-12-2007, 11:12 PM   #21
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Megasquirt diagrams all show one to ecu and other to ground. The ecu wants a 5v reference, and the setup works by using the IAT sensor as another bias resistor.

This is for the GM and other sensors just wired up.
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Old 08-13-2007, 12:00 AM   #22
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AIT on a stock harness is 2P, red with a green stripe.....6th over on the big harness on the bottom.
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Old 08-13-2007, 12:06 AM   #23
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here:




the 5vref is 2K



this will help as well:

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Old 08-13-2007, 12:19 AM   #24
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Thanks I thought it was the R/G @ 2P, but my diagram wasn't anywhere near as clear as yours.

So, one lead from the AIT sensor to 2P, and the other to the sensor ground (on the head, pass side, by fuel rail) should be the ticket. Or does 1 lead go to 2P, and the other to 2K? I dunnooo....
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Old 08-13-2007, 12:53 AM   #25
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According to MS site... one is ground other is to ecu.

But mine isn't exactly reading right yet.
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Old 08-13-2007, 10:09 AM   #26
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Hi Ben,

You should see 5 volts on pin 2P with the IAT sensor disconnected. The MSPNP sends a 5 volt signal on that line; there's a 2.49K resistor inside the MSPNP, and the IAT sensor forms the second half of a voltage divider.

So with the IAT sensor in place, you will see a somewhat lower voltage. You'll only see voltage on the red and green wire; the other wire is a ground.

Let me know what you find there; we'll get this one fixed one way or another.
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Old 08-13-2007, 12:28 PM   #27
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Thanks Matt.

Today I have 4.77V at the AFM harness.
I am going to try to re-crimp those tiny little spades onto the IAT sensor wires and reconnect to the harness. Wish me luck.
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Old 08-13-2007, 01:28 PM   #28
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AIT sensor works again.
All wiring believed to be good.
Problem suspected to be loose ribbon cable connector inside of MSPNP unit. It was not pushed firmly into the daughterboard. (my unit has been opened up 2 or 3 times for modifications)

I was not able to get a good crimp on one of the spades. The connection is more or less taped on now. I'll deal with it in the next few days.
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Old 08-13-2007, 01:45 PM   #29
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hmmm
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Old 08-13-2007, 11:08 PM   #30
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Hurm... i measure 2.41v for my temp sensor... I also compared the sensor ohm wise to another new sensor.. .and its fine.

I wonder wth is wrong with mine.
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Old 08-13-2007, 11:19 PM   #31
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Got to drive the car appx 50 miles today, temp sensor seems fine.
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Old 08-13-2007, 11:27 PM   #32
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<-- jealous
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Old 08-13-2007, 11:35 PM   #33
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haha, then I won't tell you about my WOT pull through the gears until 6100 rpm in 5th. I was going for 7k, but I let off because w/o the undertray the front felt floaty and there was oncoming traffic.

and I also won't tell you that my ignition misfires seem to have gone away since we did some ground alterations.

all-in-all, it was a good day for the miata.
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Old 08-13-2007, 11:44 PM   #34
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Then be a saint... and help me remedy my IAT issue
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Old 08-14-2007, 12:20 AM   #35
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The GM sensor may or may not be a good choice, the thermistors used in the LS1's react quite slowly, you're better off buying a thermistor for $10 in the right range....
I can supply a source and part # if you need, just chop the "cage" off the GM sensor and solder in the new, then glue cage back on, done.

the one on the GTO was quite poor and the IAT->timing tune very conservative, so at a light the IAT would go up, and the thermistor wouldn't read a cooler temp until into 4th gear, making for the suck.
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Old 08-14-2007, 12:27 AM   #36
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Now someone thinks about that... I want to at least get it running off the gm sensor first. I can muck with a nicer sensor later.

I'm running one side to 2C ground (blk/lt.grn) and 2P (iat sensor).

Going outside now (at neo's prodding) to try the ground directly to chassis/motor. I'll be back in a min.
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Old 08-14-2007, 12:30 AM   #37
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Quote:
Originally Posted by Splitime View Post
Now someone thinks about that... I want to at least get it running off the gm sensor first. I can muck with a nicer sensor later.

I'm running one side to 2C ground (blk/lt.grn) and 2P (iat sensor).

Going outside now (at neo's prodding) to try the ground directly to chassis/motor. I'll be back in a min.
why not just test it with an ohm meter?
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Old 08-14-2007, 12:52 AM   #38
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I am, it reads fine as far as i can tell. I get solid ohm readings and voltage when on.

So it must be a MS config issue... bah!
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Old 08-14-2007, 09:14 AM   #39
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black/green is a sensor-->motor ground. look over on the pass side, between the fuel rail and firewall. there's like 8 black/green wires between 2 bolts.

my car had some major grounding issues. we ended up running 2 extra main grounds from the MS to the motor. we also ran all the acccessories that were formerly grounded with the MS (gauges, wb controller) to the same ground point on the motor, but through their own wires.

yesterday was the first test ride, and I believe everything to now be good.

Philip, I'd be interested in that replacement thermistor. Though I don't see that type lack of response with my sensor. I was watching it with a close eye yesterday.
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Old 08-14-2007, 09:42 AM   #40
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www omega.com

part #44005
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