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Old 07-29-2020, 10:43 PM   #1
guciodog11
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Member#: 160264
Join Date: Sep 2007
Chapter/Region: Tri-State
Location: S.I, NY
Vehicle:
95 20G'd EJ255 GC8

Default EJ257 in a GC8-no ECU power

Hi everyone,

Completed my forged internals 257 build and dropped it into my GC. The car previously ran without any electrical issue for months. New motor worked great, idled for a total of 20+ hours before being driven. First small speed bump blew out SBF #2, which is the GC equivalent of SBF #5 I believe.

I swapped out fuses on the side of the road but a few blocks later it blew again.

Towed the car home, threw in fresh fuses, started right up without a glitch. The next morning it was completely dead: no ECU power, no CEL light with ignition on, fuel pump not turning on.

After numerous swaps of relays and fuses under the hood, The motor started up but died after 30 seconds, taking SBF #2 with it again. Replacing the fuse did nothing, same no power issue as before.

Factory wiring diagram is useless as the harness is an 05 LGT, connected to a 04 STi ECU, and merged with a 95 L body harness.

Would anyone have any tips on how to diagnose this problem? I changed every possible fuse already, and every relay under the hood. I'm at wits end with the car and seriously thinking of parting it out and going with a more reliable project car.

Thanks!
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Old 07-29-2020, 10:48 PM   #2
2slofouru
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You need to consult the person that did the merge. There may be a 12v+ wire somewhere shorting to ground if you hit a bump hard enough. Otherwise they may have run too many devices on a single 12v+ circuit and it's overheating and blowing the fuse.
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Old 07-29-2020, 10:56 PM   #3
guciodog11
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Member#: 160264
Join Date: Sep 2007
Chapter/Region: Tri-State
Location: S.I, NY
Vehicle:
95 20G'd EJ255 GC8

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Quote:
Originally Posted by 2slofouru View Post
You need to consult the person that did the merge. There may be a 12v+ wire somewhere shorting to ground if you hit a bump hard enough. Otherwise they may have run too many devices on a single 12v+ circuit and it's overheating and blowing the fuse.
The merge was done by Zephyr over 11 years ago, and he hasn't been active for over 2 years now unfortunately

Interestingly it does not blow fuses anymore, There is just no current going to either the ECU or fuel pump at all. At times it's intermittent which is the most confusing part, once every 50-60 ignition cycles the CEL and fuel pump goes on and dies.

Do you think just buying an STi harness and throwing it in would work? I dont think it would have to be merged with the body harness at all other than the RPM gauge.
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Old 07-29-2020, 11:03 PM   #4
2slofouru
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There is no reason a professionally merged harness won't handle the different engine setup. So long as their isn't wiring damage or a fried device shorting it, there's no benefit to doing more wiring swapping. The issue likely has to do with something you messed with during the swapover, like the main computer ground rings at the passenger rear side of the engine having a loose bolt or a wire being shorted because you tightened a metal part down on a section of the harness on the engine somewhere. Just keep following the harness around the engine and see if you spot anything pinched, cut, or disconnected ground rings.

Don't freak out and give up that quick, it's likely something ridiculously simple and you will laugh after realizing you almost gave up because of it.

Zephyr has a good rep, I would expect his work to be solid.
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Old 07-29-2020, 11:08 PM   #5
guciodog11
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Member#: 160264
Join Date: Sep 2007
Chapter/Region: Tri-State
Location: S.I, NY
Vehicle:
95 20G'd EJ255 GC8

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Quote:
Originally Posted by 2slofouru View Post
There is no reason a professionally merged harness won't handle the different engine setup. So long as their isn't wiring damage or a fried device shorting it, there's no benefit to doing more wiring swapping. The issue likely has to do with something you messed with during the swapover, like the main computer ground rings at the passenger rear side of the engine having a loose bolt or a wire being shorted because you tightened a metal part down on a section of the harness on the engine somewhere. Just keep following the harness around the engine and see if you spot anything pinched, cut, or disconnected ground rings.

Don't freak out and give up that quick, it's likely something ridiculously simple and you will laugh after realizing you almost gave up because of it.

Zephyr has a good rep, I would expect his work to be solid.
Oh he did great work, my old 255 worked flawlessly till it dropped a valve :/

I sure hope it's something stupid. Im going to pull my FMIC piping tomorrow and remove the harness to see if there's anything going on. I'd expect these kinds of issues immediately after dropping in the motor, but not months and hours of running time. To be fair, wiring and ECU stuff is like magic to me so I could definitely be wrong!

Thanks for the help!
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Old 07-31-2020, 05:58 PM   #6
guciodog11
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95 20G'd EJ255 GC8

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checked all the grounds, all under hood relays and still nothing...


if anyone wants a new built motor and a clean '95 L shell for cheap let me know!
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