What causes the SBF's to blow?

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James614
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What causes the SBF's to blow?

Post by James614 »

So, im drivig to lunch today and do a spirited pull in 1st gear, and it dies. After shitting bricks for a moment, I see that the CEL doesnt come on with the ignition and unsurprisingly, one of my green SBFs in the main fusebox was toasted.

This happened during my swap, but I shrugged that off as a wiring issue. Well, now I have no wiring issues. Ive been over all my grounds, im running the GD COP conversion using stock wires and connectors (but outside the main harness). And I have my AWIC pump running off the A/C circuit, which has been fine for 2 years now (long before my swap or any electrical issues). Im completely clueless as to why this would happen :-/
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
James614
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Re: What causes the SBF's to blow?

Post by James614 »

May have found my answer. After replacing the SBF and driving 50ft, it started throwing crazy knock lights and sputtering and had almost no power. Almost thought my new fuel pump was taking a shit, until black smoke started billowing from the hood scoop. After taking a moment to shit even more bricks, I checked it and found that my O2 sensor harness was set on fire from resting on my down pipe (not just melted, it was on fire and the flame was climbing towards my engine harness!). Must have forgot to zip-tie it back in place after a changed my clutch. Oh well, pulled that out and she runs fine again (is there no cEL for a bad/missing O2 sensor?)

So, I'm betting the wires grounding out on my down pipe caused the SBF to blow. Scratch what I said about not having any wiring issues ;)
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
mike-tracy
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Re: What causes the SBF's to blow?

Post by mike-tracy »

Holy shit bricks batman! Glad you figured the cause! Yeah as far as a CEL for O2 sensor issues, I've never seen them without a sensor installed. A marginally bad sensor didn't throw one for me either.
1992 Legacy SS 5mt, build in progress
Josh Colombo wrote: Mon Jan 14, 2002 10:23 am Wait....I'm confused now.
Legacy777
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Re: What causes the SBF's to blow?

Post by Legacy777 »

Which SBF blew? They should be numbered on the fuse box lid.
Josh

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1990 Legacy (AWD, 6MT, & EJ22T Swap)
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James614
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Re: What causes the SBF's to blow?

Post by James614 »

It was sbf 2.
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
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Re: What causes the SBF's to blow?

Post by Legacy777 »

SBF 2 feeds MB-3 which feeds the ignition relay, fuel pump relay, and injectors. MB-3 doesn't directly tie into the O2 sensor wiring, but hopefully fixing the O2 sensor is the issue.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
James614
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Re: What causes the SBF's to blow?

Post by James614 »

Well when you say it isn't directly tied into it, that sounds like it still goes through there somehow. I will crack open my wiring diagrams tonight (@#$%) and see if I can find anything else I should check on. Its possible the O2 sensor was a coincidence, but that's an awfully well timed coincidence.
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
wtdash
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Re: What causes the SBF's to blow?

Post by wtdash »

So....U gonna build a house....w/all those 'bricks'?
Glad you figured it out.

Td
Turbo Subies:
'87 GL-10 Turbo - SOLD
'90 BJ EJ22T/DOHC & 5speed swap - SOLD
'04 FXT, Forged internals, VF39, STI TMIC, Cobb AP- SOLD
'93 Legacy SS - 5-speed, SOLD :-(
'02 WRX -SOLD
'96 BD-turbo'd-SOLD
'98 SF - NA-T
91Beater
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Re: What causes the SBF's to blow?

Post by 91Beater »

You likely have rubbed or melted through one of the big fat wires and shorted out to something on grounded component.
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