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subpoop

red wire by the ecu/no start

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my father was given a 91 legacy wagon and it won't start. cranks fine but no spark. checked it out and found out the brain was toast, at least it smelled like it. got a new used brain and went to hook it up and found a red wire next to it that was burned in half. got a fuse holder but don't know what amp fuse to put in or what that wire does. the only book i have is a haynes which ndoesn't have a very good wiring diagram. help

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You need to find a factory service manual. You should easily find one online. 

Once you have this, find the ECU pinout schematics and trace that red wire. It’ll explain what it is, and if it’s a power wire, which I reckon it is, you’ll know what you need. 

Alternatively, use a multimeter to check continuality with the wires at the power relay and see if there’s any link there. The other wire/place to check is the permenant power wire - any red wire at the back of the fuse box and see if there’s a link.

Wires don’t just burn out either. There must be a reason such as a stez permenent power wire being removed and the exposed wiring grounding out to earth. 

Really, you *should* be able to just reconnect that wire and go from there without issue - so long as all the proper fuses are used in the fuse box under the dash and the bonnet.

All the best with it. 

Cheers 

Bennie

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went and looked at it myself instead of relying on others and found out it didn't go to the ecm but it was in a bundle of wires right next to it. tthe red wire was single on one end and the other side going up split into two wires all of them red. i need a diagram telling me where the various connectors are. this one is white and it hangs around the ecm area on the drivers side.  payday i am going to look at one in the wrecking yard because the ecm was disconnected and laying under the seat., and i was told don't try to start it without the case being grounded. i could bypass the burned wire but i want to find out what caused it first. i took pictures but cannot find my usb cord for my camera and i have a hard time transferring it to these e mails.

Edited by subpoop
more wining and bitching.

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the link I gave you above will have that kind of information.

you might have to do a little digging around to find the exact file you need, but it is there.

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i looked and still cannot find out where the red wire goes to  i twisted it back together and it cranks but no spark.. found mention of an ign relay but where is it ? the haynes book shows the ecm on the passenger side but it is definitely on the drivers side trying to see if the crank sensor has power as well as the igniter but my brain is farting right now  and i cannot figure out where the power comes in to theses sensors. i know they come from the ecm  but which wire is which? also found out the car is a 90.

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A few points:

First, if you're trying to repair wiring faults, "twisting together" wires doesn't cut it.  Either solder them or use a crimp connector (butt splice).  Twisting will not give you the reliability you need.

Second, Haynes manuals, while usually generally useful, do not contain model year specifics accurate enough for debugging electrical problems.  They just don't, and you shouldn't try to do this based on their drawings, because you'll be wasting your time chasing ghosts.  Somewhere, somehow, you need to find the exact drawings for your car.  (This is a problem across the board, not just with Haynes' Subaru manuals.)

Third, assuming your engine uses the same type of sensors as mine (which start at '95), they are passive devices that are unpowered - that's why they only have two wires.  They're called "variable reluctance" sensors, and you can think of them as sort of like the volume control on an older stereo (which are variable resistors - potentiometers  - that don't need to be "powered").  (A lot of newer audio equipment uses more complicated rotary controls like optical shaft encoders that are "active" devices and do need to be powered, but that's not what we're talking about here.)

The upshot is that if you want to see whether the sensor is producing the pulses it's supposed to, you really have to put an oscilloscope on it.

 

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2 hours ago, jonathan909 said:

Second, Haynes manuals, while usually generally useful, do not contain model year specifics accurate enough for debugging electrical problems.  They just don't, and you shouldn't try to do this based on their drawings, because you'll be wasting your time chasing ghosts.  Somewhere, somehow, you need to find the exact drawings for your car.  (This is a problem across the board, not just with Haynes' Subaru manuals.

there is a link above to a site that has FSMs for pretty much all Subarus, including 1st gen Legacy specific info (90-94)

link to the 90-94 specific stuff: http://jdmfsm.info/Auto/Japan/Subaru/Legacy_Outback/1990-1994/

Granted - the wiring diagram is labeled 1990, but it would be MUCH more useful to him than a Haynes or Chilton's could ever hope to be. 1990-1994 did not change much at all - a few minor, mostly cosmetic things.

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None of the ECU wires will be running separate from the wrapped harness.  My guess is that's an old wire someone added in. (probably poorly).  I would honestly ignore it unless you REALLY Think it's part of the factory wiring.  At any rate you can test the ignition relay and power to ECU.  

 

First, does CEL light with key on?  if so, the IG  relay is working.  and ECU has power.

Test the Yellow wire at the Alternator for 12v with key on.  If it has power, so does the rest of the injector harness and the ECU sensors. 

If that's all good and no start still I would look at the wires behind/under the throttle body.  There are connectors there, 3 on a bracket.  3 pin crank sensor(gray) 3 pin Cam sensor (white) and 1 pin for knock sensor.  Check the crank and cam sonsors  particularly.

ECU case does not need to be bolte to ground.  it grounds through the wires on the intake.  If CEL lights, ECU has ground.

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i have power to the coil and the igniter and as soon as i find my test light i will see if the test light pulses at the two outside wires at the coil.  i changed the crank sensor because the bottom was dented and changed the cam sensor and the igniter as well i found out someone put a used coil in and i measured them as well  the primary on no's 3 and  7 measured .9 ohms and the no's 1 and two measured .7 ohms the secondary was fine on both according to Haynes. so i think it is the coil. those wires are a pain to fish through to the connectors in the back. still no spark tho. how do i test the two sensors just look for the flash at the test light?

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the timing belt is fine. found out there is no power to the ecm. it is supposed to go to the yellow wire with the red trace and it is supposed to be 12v constant. there is power to the fuse and through the fuse but then it disappears i am trying to get the fuse box out because it splits off into two wires so somewhere in that mess a wire is bad or the junction where it splits is bad. if i apply 12v to the ecm can i test it that way? when i test it out on the engine the light is supposed to light up and flash in time with the crank but it doesn't light up.

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