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They're just cones!
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Discussion Starter #1
Car: B14
Motor: stock Avenir det
ECU: JWT

My car won't start. Cranks like a champ. ~12v battery voltage. Blue relay under dash buzzes, like it's not getting good power to activate. Voltage from good ground (cig lighter) to pins 56,61,70, and 113 on ECU show around 6v.

I should have battery voltage at these pins, right?
 

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They're just cones!
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Discussion Starter #2
Any guesses? Anything I can try?
 

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SR20DEtroit
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The 4 pins you mentioned all share one common fuse and one common power wire (starting at the battery). Check all fuses under the hood in the fuse/fusible link boxes by the battery.

If those fuses look good, then follow that wire from the fuse boxes to the battery (+) and check for corrosion at the ring terminal or clip at the battery, or however you have it connected.

IIRC, there is a separate power wire for the starter (goes towards the block), and a separate power wire for those fuse boxes which disappears into the fender, goes inside to the fuse box, connects to the main/interior harness and eventually to your ECU. This may explain why you're getting good crank, but a weak ECU voltage.

I think your problem may be corrosion at the battery since you are getting some voltage to your ECU.

Let me know what you find, Matt.
 

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They're just cones!
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Discussion Starter #4
I'll try that this weekend and let you know what happens. Thanks.
 

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They're just cones!
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Discussion Starter #5
Well, I just hot wired one of the pins to the +12v of the battery and it fired right up, for the first time since Easter. :biggthump

I see the wire that runs into the underhood fusebox / fusible link box. It's a clip-in piece that plugs into the battery terminal. I get proper voltage at this point, and also proper voltage at the "Engine control" fuse. After here, does it run into the interior fusebox, or right to the ECU?

Oh, and thanks Sonny, you rule.
 

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SR20DEtroit
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Well, I just hot wired one of the pins to the +12v of the battery and it fired right up, for the first time since Easter. :biggthump

I see the wire that runs into the underhood fusebox / fusible link box. It's a clip-in piece that plugs into the battery terminal. I get proper voltage at this point, and also proper voltage at the "Engine control" fuse. After here, does it run into the interior fusebox, or right to the ECU?

Oh, and thanks Sonny, you rule.
Glad you got that figured out, man. From what I remember, the power supply wires run directly to the ECU, which is weird, because there has to be some fuse popped somewhere unless we're talking melted wires (hopefully not the case). I will doublecheck EL.pdf when I get to Detroit tonight.

S
 

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They're just cones!
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Discussion Starter #7
Okay, update:

I get 12v at the relay on the ECU until I turn on the ignition. Then it drops to ~7v. This works with all three blue relays I have on hand.

There are two engine control fuses in the interior fusebox. If I pull the lower one, everything dies. I have 12v on that fuse.

Where do the white / red stripe ECU power lines get power from? The relay?

I am no electrician, so I can't figure out how I can possibly have half voltage. I figure it would either be all or nothing.

Would there be any harm in running a jumper from an ignition switched 12V source to the ECU to bypass the problem?
 

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SR20DEtroit
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I'm curious as to what your issue is, but I haven't had time to look closely at the elec diagram. Perhaps tonight.

Running a jumper from the ignition switched 12v source to the ECU should be the last resort; if this is done, however, it should be fused and the wires should go directly to the ECU and nowhere else from the ECU. In other words, run a wire from under your dash somewhere (steering column is the best place to tap into a solid connection), fuse it, then run it to the power pins by interrupting the wires at those pins (vs. tapping into... that may cause problems).

There may be all sorts of resistors, inductors, and capacitors before the WR wire; without looking at a diagram of the wiring and the components/circuitry involved w/ that magical wire, it'd be impossible to determine why you're getting 7V instead of 0.

 

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SR20DEtroit
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get 12v at the relay on the ECU until I turn on the ignition. Then it drops to ~7v. This works with all three blue relays I have on hand.
1) Which color wire is at this pin you're measuring (there's two white/blue, one white green, and one white/red)?
2) Where's your ground?
3) Can you doublecheck the voltages w/ the key in the ignition and w/ the key out of the ignition at the following pins on the ECU:
- 70
- 113
- 56
- 61
- 4

Here's the power diagram for your ECU; it goes from the battery to your fusible link box by the battery as a white/blue-stripe, and eventually turning into a white/red-stripe at pins 56 and 61 (power or backup power, whichever). Since you said that pins 56, 61 and 70 are showing the incorrect voltage, the only thing they have in common is that 7.5A fuse (pin/location 41). Doublecheck this fuse.



Here you see the inside of the fuse box and that its a 7.5A fuse; should have a white/blue-striped wire underneath it:



Physical location on the 200:



Makes its way around the driver's side fender and into the cabin:



Clusterf*ck of wires that is the main harness:



Finally to your ECU plug:



Another thing to note is that the wires also go to the EC-CMPS (camshaft position sensor, distributor)... I don't know if this could be causing an issue though. Just as a test, try unplugging the harness at the distributor, then check and see if your same relay you tested earlier goes from 12V to 7V when you go to ignition. ;)

 

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i know this is an old thread but i think im having the same problem also. When i start my car (96 200sx se with a RR swap) it will sputter and die almost immediately unless i give it gas for bout 5-10 secs, then it will idle or the ecu will lose power and then die. Ive chased wires and found that there is a power wire goin from the ecu to the coil which is not gettin 12v. (safe to say ecu isnt either?) I also cant get a reading from my tps...I will try running a power wire to the ecu and see if that fixes my issue also...
 
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