Fuel pump stops when release break pedal (Legacy 92).

[geo_a]

Subaru Legacy 1992 (turbo)

The car starts normally with breaks applied, however, as soon as I release break pedal the engine chokes and dies.

At the beginning the problem occurred occasionally, about twice a year and I didn’t pay much attention to it, as I could eventually start the car after few tries. But once I couldn’t manage to start it and the car was towed to a garage. They replaced the fuel pump. The problem reoccurred few months later and became persistent.

This time I tried to figure out the problem myself (I know very little about cars, please be easy on me).
I discovered that releasing break pedal cuts off current to fuel pump (there is a switch under the pedal but I don’t know how it relates to ECU or the relay). As long as I hold the break the engine runs fine. The pump itself works fine (I have wired the pump bypassing the relay, through a manual switch, and it works). I suspected the fuel pump relay, so I switched the fuel pump relay with the sunroof one but this didn’t help (I hated removing the dashboard!!!). There is an error code flashing but I am not sure how to read it.

Any insights, ideas, suggestions? Could this be ECU (ouch)?

Thanks in advance
George

[Binford]

Bad ground? Only thing I can think of is something bad (coroded) in the wiring itself. Have you checked the connector under the rear seat?

[vrg3]

Welcome to Legacy Central, George. Please take the time to glance through all the sticky threads in each forum.

The pump itself works fine (I have wired the pump bypassing the relay, through a manual switch, and it works).

Can you explain this more? How did you do this wiring? Was the car driveable while this bypass was in place?

Also, do the brake lights work correctly? Both when the car is on and when it's off?

When the fuel pump cuts off and the engine stalls, does the "Check Engine" light on the dash turn/stay on?

You say there's an error code flashing -- now that you know how to read engine trouble codes you can clarify.

This is an odd problem. As Binford says, it may be a bad ground. The fuel pump and brake lights do share the same ground paths. I'm having trouble thinking of a way that ground failing could cause this problem (if anything, it seems like it would go the other way -- pressing the brake pedal would kill the pump), but bad grounds are known for causing weird symptoms.

The two grounding points that both these devices use are as follows:

1) Under the right front seat. To access it, you remove the seat and peel back the carpet. There are two grounding points on the little ridge running laterally across the car; this one is the outboard one. If you have ABS (all American turbos do), the ABS computer is actually held in place by the screw that goes through this grounding point.

2) In the rear, either behind the left taillight (if it's a wagon) or somewhere behind the trim at the back part of the trunk (if it's a sedan). If it's a sedan, the wire comes off the harness between the two license plate light connectors.

You could try inspecting one or both of these ground points, and maybe run a new 10 AWG ground wire from there (or from the black wire on the fuel pump assembly) to the engine block.

[geo_a]

Can you explain this more? How did you do this wiring? Was the car driveable while this bypass was in place?

I found a wiring in the trunk that connects a break switch (under the break pedal) with tail lights and fuel pump. When I apply breaks, the same current that powers tail lights goes to the fuel pump. The fuel pump wire is separated from tail lights circuit by a diode (also in the trunk, under a rug). Now I am not sure if this is original by design (to power up the pump by applying breaks) or it was added by previous owner for some reason. I haven’t seen this part on a diagram. Do you guys know if this is by design?

I connected a permanent 12v to that wire that connects the fuel pump (in the trunk) and added a switch next to the driver seat. Basically, I power up the pump directly. The car is drivable but feels out of tune. Sometimes after 30-40 minutes of driving I start hearing a little rumbling noise coming from front/left and at the same time I feel loss of power, not very significant (just enough to feel that something is not right). After a minute or two the car starts stalling. After I stop and restart the engine the problem goes away. On rare occasions when I can start the car and drive w/o using the bypass, it drives perfectly.

Also, do the brake lights work correctly? Both when the car is on and when it's off?

Yes the break lights work fine.

When the fuel pump cuts off and the engine stalls, does the "Check Engine" light on the dash turn/stay on?

After the engine stalls the “Check Engine” light stays on together with all other dashboard lights.

You say there's an error code flashing -- now that you know how to read engine trouble codes you can clarify.

The “Power” light flashes only after I drive with the bypass. There are 16 short flashes, but I am not sure how to read them. Maybe this is related to my tweaking and not the original problem? I am sooo confused! When I don’t use the bypass and the engine stalls on startup - there are no error codes flashing. I measured today voltage from the fuel pump relay (BR wire) and it seems fine: there is a signal on ignition and it stays on for about 1-2 sec after the engine stalls. I also hear a click coming from the fuel pump on ignition.

You could try inspecting one or both of these ground points, and maybe run a new 10 AWG ground wire from there (or from the black wire on the fuel pump assembly) to the engine block.

I cleaned the connector under the passenger seat (I hope I found the right one but no luck. Tomorrow I will try to run extra ground wire to the pump, as you suggested, and check other ground connectors.

Thanks guys so much for your tips!

[Legacy777]

Sounds like you have electrical issues/short/alternator, or something.

Read the codes from the ECU & TCU.

Instructions
www.surrealmirage.com/subaru/engine.html
www.surrealmirage.com/subaru/trans.html

[geo_a]

I disconnected today the power pump from the tail lights circuit and the car started normally. Restarted the engine dozen of times, drove around the block – it worked!

It looks like faulty diode drained current from the pump. I still don’t know why the pump was wired to the break switch but I suspect that was added for some reason (???) and was not manufacture’s design.

Josh, thanks for posting the links. I connected black testing connectors as per Engine Tips and the “Check Engine” light constantly flashes with interval about 1 sec. There are no short-long sequences, just a permanent blinking with the same interval. Does this mean there are no error codes in memory?

[vrg3]

Woah. That is weird. The brake light circuit and the fuel pump circuit are definitely not supposed to be wired together at all. Maybe a previous owner was high when doing some repairs or something.

Something still may be weird about your fuel pump wiring... I don't see how the diode could drain current from the pump without popping a fuse unless the wiring to the pump is in very bad shape.

[subawhatsubawho]

Part of some sort of anti-carjacking or some sort of weird alarm system???

[vrg3]

Maybe.

[Legacy777]

Josh, thanks for posting the links. I connected black testing connectors as per Engine Tips and the “Check Engine” light constantly flashes with interval about 1 sec. There are no short-long sequences, just a permanent blinking with the same interval. Does this mean there are no error codes in memory?

Yeah, if you get steady blinking of the CEL, there are no codes stored.