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ECU wiring for RWD Datsun

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Alex7747

10+ Year Contributor
1,050
5
Sep 27, 2010
Hesperia, California
-'95 eprom ecu
-'97 wire harness
-1g CAS, wired up the Magnus way.. http://magnusmotorsports.com/wp-content/uploads/2010/02/1gina2g.pdf
-6 bolt 4g63t

Okay so I'm at a point where i can beginning doing the wiring for my Datsun. I have the ecu pinouts and i need some help..

I have tried hooking pins 12, 25, and 80 to a 12v source and grounded pins 13, 26 and 92 .http://www.dsmlink.com/images/forums/2GECUPinout.pdf I also grounded all the wires that need to be grounded on the wire harness. But the ecu is not sending and spark to the coils. Is there anyone that can help me manually hook up the use like the guy in the video below??

Does anyone know how this guy did this?! [ame=http://www.youtube.com/watch?v=19Of_BPlbvQ]4G63 Wiring Harness Testing Indoors - YouTube[/ame]

Edit: I found a diagram the guy in the video made...4G63 | HotrodCoffeeShop
Half way down under "91-94 wiring diagram"... How does this look to everyone?
 
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Nice diagram

As far to how the guy did that, he just powered up the harness and replaced the 4g63 with a cordless drill.

I've done that before with the harness on the car just to save the starter and all the dry cranking.
 
Yeah, it took me awhile to stumble on it, and its funny because the guy was replying to a question gafro asked(youtube) and i looked into what he was saying and found the diagram. He's actually a member on here, hopefully he can reply and help me out.

Once i have a 91-94 ecu ill be giving this a try. But its been a while since iv had a DSM so does anyone know the differences if any from 1g sensors and 2g sensors, are they interchangeable? exclude the '90, i know its completely different. Im talking 91-94 and 97-99...

Ignore: http://www.dsmlink.com/images/forums/1GECUPinout.pdf
 
Okay i was back in the garage today trying to get the ecu to just turn on. I assume when pin 36 (the CEL wire) sees 12v it means the ecu is on, correct?

Anyway, i got pin 38 (MFI relay control) and pin 80 (backup power supply) and hooked them up to 12v and got 12v at pins: 36 (CEL), 12(power), 25(power), 92(sensor ground), 13(ground), and 26(ground). Why are pins 92, 13, and 26 getting 12v of power when they are supposed to be grounded?

So next, i grounded pins: 92, 13, and 26, and got 0v across the board.. I'm lost.
does the ecu turn on with just power and no ground?? :confused::confused:
 
Anyway, i got pin 38 (MFI relay control) and pin 80 (backup power supply) and hooked them up to 12v and got 12v at pins: 36 (CEL), 12(power), 25(power), 92(sensor ground), 13(ground), and 26(ground). Why are pins 92, 13, and 26 getting 12v of power when they are supposed to be grounded?

So next, i grounded pins: 92, 13, and 26, and got 0v across the board.. I'm lost.
does the ecu turn on with just power and no ground?? :confused::confused:

You shouldn't have seen +12 on 92(sensor ground), 13(ground), or 26(ground). Are you sure you are counting the pins correctly?

Grounding those when they have power on them is a quick way to burn up the ECU if you don't have a small fuse in the power lead.
 
You're the guy i was hoping to hear from LOL.

Im positive i counted the pins right. When i send power to pin 80 alone and ground nothing, i still see 12v at all the grounds and pin 80 is supposed to see constant 12v. does that mean my ecu is done? Im very confused with the results i got.
 
I've never tried applying 12v to pin 80 alone. It's common practice with connectors that might be inserted while powered to connect the ground pins first and I follow that manually when I work on things. You want the low resistance grounds established before applying power so the current doesn't flow down a side path.

Remember that the diagrams all show the pin out from the perspective of looking into the connector that accepts the plug, so the ECU pin out is looking into the ECU connector.

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My test harness has ground wires to pins 13 and 26.
A fused 12v lead that goes to pin 80, via a relay to pins 12 and 25, and via a switch to pin 92.
It has a connection from pin 38 to the coil of the relay and from the other side of the relay coil to the fused 12v.

I plug it in, turn on the power supply, and flip the switch to turn the ECU on. The ECU will see 12v at pin 92 and pull pin 38 low activating the relay which applies power to pins 12 and 25 completing the power up process.

At that point pin 36 will also go low for five seconds to cause the CEL to turn on, not provide 12v. Most of the signals that ECU asserts are via pulling an external voltage to ground. Those external signals are current limited by either the sensor/solenoid or by the circuit that biases it.

If you look at the wiring diagram you'll note that the CEL light gets powered on one side and the other is connected to the ECU. When the ECU pulls it's pin to ground current flows and when the ECU turns it off the voltage floats back up to close to battery voltage. Same deal with relay coils and injectors.
 

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Okay Steve, i did what you said, and now when i hook the ecu up (12v, and ground) i get 12v at the appropriate plugs, MAF, injector resistor box, cas, O2, isc, (power wire) etc. and 0v at all the grounds, so i think I'm on my way, But I'm not sure what that means... Is there any way to verify the ecu is in fact on? i have all the sensors but the o2 and MAF. However i do not know if my cam sensor is good, its very old. I checked the resistance on my coil pack, at the plug, and i got nothing so I'm guessing the coil pack is done.


Steve, what are your thoughts on the wire diagram above (hotrod cafe) in my first post? Would it be easier just to sell my ecu and go out and find me a 1g ecu and harness and start over and follow that diagram to the "T"? From the looks of the diagram do you think it'll work?
 
Jeremy, thank you for posting that! i could not find that page and ive been looking for weeks now. is the diagram brendon made know to work? my harness is hooked up about 95% like that one. i just have to made small adjustments and itll be exactly like that one. thank you so much ill post back once i make the corrections.

Okay, so i did exactly (checked twice) what the 2g diagram said to do in the link you provided and i got nothing again. Maybe my MFI relay is bad. any ideas?
 
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