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Old 04-23-2012, 01:00 PM   #1
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Default Electrical expertice needed! and can TPS and MAP sensor share power and ground?

I currently have a GM 3 bar MAP sensor wired through the MAF harness, but getting power from the TPS 5v wire. I have wires running directly from the IAT to the ECU (I set it up this way when I installed my MS1). The 2 sensors are currently sharing the ground when connected this way, if I'm not mistaken.

Two reasons I ask this question:

-I originally got power from the TPS as a quick, easy way and used a vampire tap - I hate these and don't trust it. I would like to make the install cleaner, and using the 5V from the MAF harness would do that.

-The larger issue is that I'm having a really weird problem that I'm now thinking is related to my wiring somehow (Originally I thought it was my AEM unit or calibration):
- When I apply any throttle at all, the engine stumbles and dies. What makes me think it's an electrical issue is that the same behavior occurs when I hook up a timing light and pull the trigger. It's like the electrical load causes the car to stall. But not just any load, because I can turn on the A/C and the engine continues to run.
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Old 04-23-2012, 01:01 PM   #2
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IAT isn't powered, so no.
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Old 04-23-2012, 01:06 PM   #3
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Um, duuuh. I knew that I swear. I shouldn't post when I'm at work. Wrong question I guess. Have to edit the title.

What I really am asking is if I can get power for the MAP sensor from the AFM harness, and if there will be any issue with using that. I've seen several posts and articles where power is sourced from the TPS and I'm wondering why the AFM 5v isn't used instead.
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Old 04-23-2012, 01:07 PM   #4
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OK, can't edit the title..
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Old 04-23-2012, 01:09 PM   #5
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the TPS 5v is sourced from the AFM harness on the 90-93.


but yeah, since both are input sensors they should share the same ground, and since both need 5v for power, they should share the same power as well.
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Old 04-23-2012, 01:35 PM   #6
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No problems with this at all.

There is only one +5 Vref from the ECU, and it's ultimately going to wind up feeding all of the sensors which need +5 (TPS, MAF/VAF/MAP, EGR, etc). So it matters not in the least whether these feeds are spliced into a common line or made as home-runs to the ECU.

The same applies to sensor ground.
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Old 04-23-2012, 01:47 PM   #7
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OK, so the Red/Blk wire from the AFM part of the harness - is this 5v? I saw in an old post that it was listed this way (https://www.miataturbo.net/megasquirt-18/94-95-96-97-maf-delete-discussion-14166/), but when I look at the 95 wiring diagram it doesn't seem to connect back to the 5V ref. supply. Looks like it goes to 2P, which the AEM chart lists as IAT/ Air Temp.
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Old 04-23-2012, 01:48 PM   #8
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So any thoughts on how the hell the timing light is causing the engine to stall? Seems really weird....
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Old 04-23-2012, 01:48 PM   #9
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its actually 2K
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Old 04-23-2012, 02:24 PM   #10
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Quote:
Originally Posted by Braineack View Post
its actually 2K
The 5v reference is 2K, correct. The Red/Black wire from the AFM goes to 2P.

I'm just trying to determine if there is a solid 5v wire at the AFM connector that I can use to power the MAF.
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Old 04-23-2012, 02:26 PM   #11
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2P is the AIT sensor input. the MAF doesn't have a 5v soure IIRC.


the 5v wire is lt green/white. goes to the EGR and TPS from 2K
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Old 04-23-2012, 02:34 PM   #12
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Quote:
Originally Posted by soloracer View Post
I'm just trying to determine if there is a solid 5v wire at the AFM connector that I can use to power the MAF.
I'm confused by the use of the terms "AFM" and "MAF" in this context. Is this for your '95 or for a '90-'93 car? (We typically use the term AFM to refer to the VAR sensor on the 1.6 engines, and the term MAF to refer to the hotwire sensor on the 1.8 engines. No Miata had both an AFM and a MAF.)


In the stock wiring harness for a '95, there is not a supply of +5 at the MAF sensor connector. The MAFs in the 1.8 cars are all supplied with +12 from the main relay.

If you are using an external IAT sensor, then you can hijack the wire that used to feed IAT from the MAF to the ECU, and back-feed 5v into this wire from the ECU to whatever thing you have plugged into the MAF sensor connector.
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Old 04-23-2012, 02:35 PM   #13
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Quote:
Originally Posted by Braineack View Post
2P is the AIT sensor input. the MAF doesn't have a 5v soure IIRC.


the 5v wire is lt green/white. goes to the EGR and TPS from 2K
OK. That's what I thought. I was confused by the pinout in the post referenced above. The OP in that discussion had indicated that there was a 5v wire. Looks like there isn't. So basically I just need to make that TPS wire connection neater or pull power from EGR line if I want to ditch the vampire tap.
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Old 04-23-2012, 02:38 PM   #14
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Sorry, that should have read "MAF connector that I can use to power the MAP."

Trying to do too many things at once....

Quote:
Originally Posted by Joe Perez View Post
I'm confused by the use of the terms "AFM" and "MAF" in this context. Is this for your '95 or for a '90-'93 car? (We typically use the term AFM to refer to the VAR sensor on the 1.6 engines, and the term MAF to refer to the hotwire sensor on the 1.8 engines. No Miata had both an AFM and a MAF.)


In the stock wiring harness for a '95, there is not a supply of +5 at the MAF sensor connector. The MAFs in the 1.8 cars are all supplied with +12 from the main relay.

If you are using an external IAT sensor, then you can hijack the wire that used to feed IAT from the MAF to the ECU, and back-feed 5v into this wire from the ECU to whatever thing you have plugged into the MAF sensor connector.
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Old 04-23-2012, 02:41 PM   #15
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Quote:
Originally Posted by Joe Perez View Post

....If you are using an external IAT sensor, then you can hijack the wire that used to feed IAT from the MAF to the ECU, and back-feed 5v into this wire from the ECU to whatever thing you have plugged into the MAF sensor connector.
Hmm, this gives me an idea. I don't want to do that exactly just because I don't want to mess with the stock harness layout. However, I removed the stock MAF connector and pins, and replaced with a weatherpak connector which just happens to have an extra spot....
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Old 04-24-2012, 10:25 AM   #16
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Looks like the timing light thing actually was a crappy calibration file after all. I created a new one using my old MS1 spark map, and it really improved things.
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