BRAT fuel system issues

[The Chariot]

I bought a Subaru Brat (manufactured 10/85) that needed some work.  I have done a lot of work already, but one thing I am perplexed on are the issues with the fuel system.  The previous owner (before the owner I bought it from) had an aftermarket fuel pump rigged up under the bed with it being powered by wires running inside the cabin and connected to the radio harness.  This is obviously not an ideal situation and I want to get things back to normal.  What I discovered though is two issues.  Issue #1) I assume the reason they ran their own wiring is because I am only getting 2.7V when the key is turned to the last position before cranking which will not activate the pump (I bought a brand new pump which I confirmed to be in working order when hooked to 12V).  I figured maybe there is a bad ground, so I ran a ground wire directly to the battery and tested again with the multi-meter to get the same result.  Issue #2) They had the fuel supply line connected to the smaller return nipple of the gas tank and the return line from the engine was capped off.  I discovered the reason for this is because the larger nipple that feeds the fuel supply line is plugged up inside the tank.  I stuck a hose on there which I could neither suck nor blow via the power of my lungs.  I could use a compressor to add more pressure and see what happens, but I am not sure if I could do some damage that way.  I read about an internal sock that can get clogged up.  Any ideas on what to do with either of these issues would be greatly appreciated.

[naru]

Where are you getting 2.7 ?

The pump should have 0.0 volts unless the engine is actually turning.

[The Chariot]

Where are you getting 2.7 ?

The pump should have 0.0 volts unless the engine is actually turning.

There is 2.7V coming through the wiring of the pump harness at the last key position before cranking, then 0.0V when cranking.

[naru]

Normally,the pump is powered by a special relay called a revolution sensor.

It will only power the pump when it sees primary ignition pulses from the coil.(engine must be turning)

Pump voltage SHOULD be 0 or 12V.

Not uncommon for those relays to go bad and be difficult to source thus the wiring hack job.

The revolution sensor is located either under the dash or hood depending on year/model.

Not sure about yours.

Search revolution sensor for more info.

 

I would add a normal relay triggered by the ignition switch if unable to source a revolution sensor.

You lose the safety feature of the pump stopping w/the engine then though.

 

Some folks have cleared the tank line/sock w/compressed air.

Subaru stupidly made the sock non-servicable.

Only car I have ever heard of w/this terrible feature.

[GeneralDisorder]

You will have to drop the tank most likely and open it up (cut it open) to service the "sock" which is a metal mesh tube of sorts. Probably best to take the tank to a radiator shop, etc and have it redone. 

 

The Fuel Pump Control Unit (FPCU or Revolution Sensor if you prefer) is mounted to the bracket for the hood release cable near the handle under the dash. It's either a 6 pin block box or a 5 pin blue box depending on computer controlled carb or not. In the more common black 6 pin unit it also controls power to your choke. 

 

Yes the factory one is getting hard to source. You can use an aftermarket unit to do the same job. Don't bypass or the engine could continue running in an accident:

 

https://www.amazon.com/Revolution-Electronics-Electric-Controller-Primes/dp/B00BNZ05JM

 

GD

[Subaru Scott]

You will have to drop the tank most likely and open it up (cut it open) to service the "sock" which is a metal mesh tube of sorts. Probably best to take the tank to a radiator shop, etc and have it redone. 

 

The Fuel Pump Control Unit (FPCU or Revolution Sensor if you prefer) is mounted to the bracket for the hood release cable near the handle under the dash. It's either a 6 pin block box or a 5 pin blue box depending on computer controlled carb or not. In the more common black 6 pin unit it also controls power to your choke. 

 

Yes the factory one is getting hard to source. You can use an aftermarket unit to do the same job. Don't bypass or the engine could continue running in an accident:

 

https://www.amazon.com/Revolution-Electronics-Electric-Controller-Primes/dp/B00BNZ05JM

 

GD

 

Hey cool! I never knew those existed.

 

You can also hook it up with a relay, triggered from your oil pressure switch.

[Subaru Scott]

BTW, now that I think about that, if you do a relay off the oil pressure switch, you will probably want a prime circuit. You could do this with a momentary push button, or with a wire from the start circuit, with a diode to keep the pump circuit from backfeeding the starter.

[GeneralDisorder]

Unless it's a digi-dash car or DL model it will have a gauge sender and not the pressure switch. 

 

But yes GM used pressure switches as primary or backup fuel pump control on many of their vehicles. You can do it that way if you prefer.

 

GD

[Subaru Scott]

Unless it's a digi-dash car or DL model it will have a gauge sender and not the pressure switch. 

 

But yes GM used pressure switches as primary or backup fuel pump control on many of their vehicles. You can do it that way if you prefer.

 

GD

Yes, good point. You will need to add an oil pressure switch if you have a gauge.

[The Chariot]

You will have to drop the tank most likely and open it up (cut it open) to service the "sock" which is a metal mesh tube of sorts. Probably best to take the tank to a radiator shop, etc and have it redone. 

 

The Fuel Pump Control Unit (FPCU or Revolution Sensor if you prefer) is mounted to the bracket for the hood release cable near the handle under the dash. It's either a 6 pin block box or a 5 pin blue box depending on computer controlled carb or not. In the more common black 6 pin unit it also controls power to your choke. 

 

Yes the factory one is getting hard to source. You can use an aftermarket unit to do the same job. Don't bypass or the engine could continue running in an accident:

 

https://www.amazon.com/Revolution-Electronics-Electric-Controller-Primes/dp/B00BNZ05JM

 

GD

I located the FPCU on my BRAT.  It happens to be the black box with 6 pins.  I hope I salvaged one of those from a previous Subaru, but am not able to visit my storage to check right now.  On the tank, I wonder if using compressed air is worth a shot or should I be concerned that could blow the sock to bits or damage something else in there?

[Subaru Scott]

I would try blowing it out, just start slow. Seems to me you got nothing to lose 

[The Chariot]

I would try blowing it out, just start slow. Seems to me you got nothing to lose 

That is what I am leaning towards unless I hear otherwise. 

[Bratastick]

I could not get my fuel line to unstop even after cutting the tank open. There is one 90 degree bend and one 180 degree bend and the line was completely solid at the end where the sock was. The actual sock was fine, just the line was plugged. Ended up cutting the line and removing it, unplugging it then silver soldering it back in place. Don't think you could hurt anything with compressed air, maybe you will have success. You can see the pickup w/ sock if you remove the sender unit.

[GeneralDisorder]

It may (probably will) plug up again. Call your local radiator shop. It's not as expensive as you think. About $200 usually. Well worth it to have an epoxy lined tank.

 

GD

[The Chariot]

I could not get my fuel line to unstop even after cutting the tank open. There is one 90 degree bend and one 180 degree bend and the line was completely solid at the end where the sock was. The actual sock was fine, just the line was plugged. Ended up cutting the line and removing it, unplugging it then silver soldering it back in place. Don't think you could hurt anything with compressed air, maybe you will have success. You can see the pickup w/ sock if you remove the sender unit.

Good to hear from someone who encountered this problem.  Was it crud that got sucked through the sock and plugged up the line, or corrosion on the interior of the line itself?  I assume it was just some crud since it sounds like you reused the same line that was in there.

[Bratastick]

I think it was just a build up of sediment over time. There was a lot of crap in the tank. The baffles had pretty much rusted away and all of that was on the bottom. The bottom of my tank was actually coated with a tar like substance. I think it was some sort of sealer from the factory. It was compromised so I had to remove it.

 

I did a write up on my repair. The car had been sitting for an extended period of time, probably 20 years.

 

http://www.ultimatesubaru.org/forum/topic/161908-anybody-ever-cut-open-their-fuel-tank/?hl=%2Bopen+%2Btank 

[The Chariot]

I think it was just a build up of sediment over time. There was a lot of crap in the tank. The baffles had pretty much rusted away and all of that was on the bottom. The bottom of my tank was actually coated with a tar like substance. I think it was some sort of sealer from the factory. It was compromised so I had to remove it.

 

I did a write up on my repair. The car had been sitting for an extended period of time, probably 20 years.

 

http://www.ultimatesubaru.org/forum/topic/161908-anybody-ever-cut-open-their-fuel-tank/?hl=%2Bopen+%2Btank 

Wow.  That fabrication is really something.  Glad to see the write up and pictures as well to get an understanding of how those lines run around inside.  I can imagine mine has a bunch of crud in there too.

[The Chariot]

UPDATE:  I found a fuel pump control unit in my storage area!  Upon replacing the previous one, I did a voltage test again which revealed I was getting about 9.5V at the pump wiring harness when cranking although it would jump briefly to about 11.5V as I toggled the key back to stop cranking.

 

As for the gas tank, I blew 115 PSI into the fuel supply nipple and that broke nothing loose.  I also poked wire in there which I got it to go probably 20 inches until it stopped, but no progress with that either.  So... I went ahead and rigged up the fuel supply hose to the fuel return nipple (bass ackwards) like they had it rigged up when I bought it (and also capped the return line).  I cranked it over a bit and sure enough the BRAT fired up and ran pretty smooth.  So at least I got somewhere, but obviously not ideal in its current state of being.

I was glad to have it running, now I am curious if that was a bad idea capping off the fuel return line in order to get it running.  I am hoping to fire it up again soon just to move it around the property and tinker with it, but not sure if I could be doing damage.

[Bratastick]

I ended up having to use a drill bit to dig out part of the crap in there so there was no way air pressure would have done it. The return line is a lot smaller than the supply, but it may provide plenty of flow. 

[The Chariot]

I ended up having to use a drill bit to dig out part of the crap in there so there was no way air pressure would have done it. The return line is a lot smaller than the supply, but it may provide plenty of flow. 

Having the fuel supply line connected to the smaller fuel return nipple does seem to provide enough flow, at least while parked there.  Driving it under load may make a difference, but apparently the previous owners had driven it that way.  The fuel return line is capped off because it has no place to go and I am not sure what effects or consequences that may have.

[Bratastick]

The return line inside my tank had pin holes in it at the top of the 180 degree bend. It would not have substituted for a supply line. Your tank is probably in better shape than mine was.