ECU keep alive

[Bicyclops]

Wiring my '02 donor S after a severe diet as in basically everything stripped out of the harness. I'll be disconnecting the battery using a contactor. Can't help myself. I'm an aircraft guy. ;-) I'll have an always hot buss for stuff that needs to be. Which ECU connectors have to be all the time hot? I'll have hazards on the hot buss. Anything else I should put there?

Ed Holyoke

[lance corsi]

You’ve described my system. Using contactors to power up everything else. I will also be using a garden tractor battery. Had a fancy agm braille battery but it didn’t make it. I think the ecu is all that needs constant power.

[Bob_n_Cincy]

My under dash disconnect switch turns of everything including the ECU. If i don't expect to drive it for a few days, I turn it off.

I use a 10 lbs AGM powersports battery (Jetski battery). If the leave my switch on, it will suck my battery down in 30-60 days.

After having my disconnect switch off, my engine takes a few extra revolutions to start.
Bob


Info added for +12 Memory power for ECU
02-05 WRX ECU pin D10
06-07 WRX ECU pin B5
04-07 STI ECU pin B19
04-07 FXT ECU pin B19

[Bicyclops]

Hmmm.... I was thinking that I didn't want to erase any learning the ECU does and start over every time, but what do I know? Seems like there's more than one wire carrying current to the ECU. Do they all want to stay hot?

Seems like I read somewhere that there's a wire to the instrument cluster that wants to stay hot to keep the trip odo, too.

I'm using an Odyssey PC 680. Got 5 years out of a pair of those in my plane. Pricey but solid. You don't want to run it all the way down and not immediately recharge it, tho. Sulfates. I used two of them because I have two electronic ignitions - no magnetos to keep it running if I mess up the electron supply.

In my airplane I use battery contactors that disconnect everything except a battery buss that keeps my EFIS from forgetting what time it is. Takes the GPS longer to figure things out when it doesn't know what time it is.

Ed

[Bob_n_Cincy]

Hmmm.... I was thinking that I didn't want to erase any learning the ECU does and start over every time, but what do I know? Keeping the memory powered is best, Turning the switch off is the same condition as swaping the battery.

Seems like there's more than one wire carrying current to the ECU. Do they all want to stay hot? No, othere wires that power all the sensors and actuator that would drain the battery quickly. The other wires that bring 12 volts to the ECU are all turned off by the ignition switch.

Seems like I read somewhere that there's a wire to the instrument cluster that wants to stay hot to keep the trip odo, too. That is True, I persoally don't really care if the trip odomerter reset every time I turn off the battery.

I'm using an Odyssey PC 680. Got 5 years out of a pair of those in my plane. Pricey but solid. You don't want to run it all the way down and not immediately recharge it, tho. Sulfates. I used two of them because I have two electronic ignitions - no magnetos to keep it running if I mess up the electron supply.

In my airplane I use battery contactors that disconnect everything except a battery buss that keeps my EFIS from forgetting what time it is. Takes the GPS longer to figure things out when it doesn't know what time it is.

Ed

Bobs comments in red

[Bicyclops]

Info added for +12 Memory power for ECU
02-05 WRX ECU pin D10
06-07 WRX ECU pin B5
04-07 STI ECU pin B19
04-07 FXT ECU pin B19

Thanks, Bob.
So that's the black/red wire on B137 on the '02 WRX?

That seems to also pick up the fuel pump relay and the main relay among other things. I was figuring to wire those separately to fuses after the battery contactor. When I think about it, the main relay may be superfluous if the batt contactor is shutting off everything but the memory. Oh wait, there's the accessory position on the key switch. Don't know that I'm running much on that.

Speaking of fuel pumps, I am running two AEM pumps (one in a swirl pot). Do you think the stock fuel pump controller is good for both of them ampwise? I guess the alternative would be to use the fpc for the swirl pot and just let the lift pump run full tilt on a separate relay. It won't make any pressure to speak of, just overflow back to the tank.

Ed

[Bicyclops]

I'm hoping to not be letting the car sit long enough to run the battery down here in (currently) rainy SoCal. ;-) I'm thinking that trip ODO will be useful for figuring gas mileage and is my fuel gauge anything like accurate.

Ed

[Bob_n_Cincy]

Thanks, Bob.
So that's the black/red wire on B137 on the '02 WRX? That is correct

That seems to also pick up the fuel pump relay and the main relay among other things. I was figuring to wire those separately to fuses after the battery contactor. When I think about it, the main relay may be superfluous if the batt contactor is shutting off everything but the memory. Oh wait, there's the accessory position on the key switch. Don't know that I'm running much on that.

Speaking of fuel pumps, I am running two AEM pumps (one in a swirl pot). Do you think the stock fuel pump controller is good for both of them ampwise? I guess the alternative would be to use the fpc for the swirl pot and just let the lift pump run full tilt on a separate relay. It won't make any pressure to speak of, just overflow back to the tank. I do NOT think the fuel pump controller can handle 2 pumps. The fuel pump controller veries the speed of the pump depending on engine load. So the FPC should control the pump feeding the fuel rails. The pump feeding the swirl pot can run off the fuel pump RELay.

Ed

Bob

[Bicyclops]

Bob

That is what I was thinking, Bob. As I understand it, the fpc slows the pump down when the car is idling or at low power so as to not needlessly heat the fuel up by over pumping when there would be no problem maintaining rail pressure.

It looks as if the instrument cluster hot wire is A10, a blue/red wire in the green connector I10. On page METER-04 it is labeled POWER CIRCUIT and traces back to what looks like a straight battery + connection through a fuse of unknown amperage.

Ed

[Dave 53]

Thanks, Bob.
So that's the black/red wire on B137 on the '02 WRX?

That seems to also pick up the fuel pump relay and the main relay among other things. I was figuring to wire those separately to fuses after the battery contactor. When I think about it, the main relay may be superfluous if the batt contactor is shutting off everything but the memory. Oh wait, there's the accessory position on the key switch. Don't know that I'm running much on that.

Speaking of fuel pumps, I am running two AEM pumps (one in a swirl pot). Do you think the stock fuel pump controller is good for both of them ampwise? I guess the alternative would be to use the fpc for the swirl pot and just let the lift pump run full tilt on a separate relay. It won't make any pressure to speak of, just overflow back to the tank.

Check out the 2-13-22 "Surge Pump Return Hose" thread in the fuel system forum that discusses wiring 2 fuel pumps.

[Rob T]

My fuel pump controller started to flake out at the track and blew up two track days before I knew what was going on. I use my car on the track only. Rather than replace it, I have bypassed the fuel pump controller and put in a separate switch and relay for the fuel pump. The advantage of this is that I can crank the engine after it sits for a while to get the oil pressure up, before enabling the fuel pump and it starts. I haven't noticed any adverse impacts of doing this in the 6 or so track days since I made the mod.

[Bicyclops]

Thanks, Rob.

I can only hope to track the car at some point. I've got it set up to survive that if I get there with swirl pot and dry sump. She'll primarily be a street car. We've got some lovely canyon roads around here I can't wait to try.

A switch for the fuel pump doesn't sound like such a bad idea. They say to disconnect the crank position sensor for the oil pressure build before first engine start. What a pain to get to though. I'm thinking about pouring some oil into the engine to help prime the sump pump. Might take a while to suck it up there.

I don't pretend to know what I'm doing. It's always been motorcycles, trucks, and airplanes before this. I will be able to monitor fuel temperature but I don't even know how much above ambient is wrong.

Ed

[Bicyclops]

Check out the 2-13-22 "Surge Pump Return Hose" thread in the fuel system forum that discusses wiring 2 fuel pumps.

Thanks, Dave.

My harness is chopped into pieces so I don't really have to worry about locating where splices are for the most part, just have to wire every little thing up and hope I don't miss anything. The aftermarket fuel controller looks like it could handle both pumps what with a 30A fuse and all. I think I'll wire the OEM controller to the surge tank pump and let the tank pump run full tilt for now and see if it causes problems.

Ed

[Bicyclops]

You’ve described my system. Using contactors to power up everything else. I will also be using a garden tractor battery. Had a fancy agm braille battery but it didn’t make it. I think the ecu is all that needs constant power.

Howdy Lance,

Thought I'd share how I'm doing mine. I have the battery hot wire landed on a contactor. A #8 wire goes from that terminal through a slow blow fuse to a six position fuseblock - battery buss. The contactor coil is switched through the key sense switch on the steering column. When I insert the key, the contactor closes sending current to a starter contactor through a buss bar. It also feeds a series of slow blow fuses which in turn feed more fuse blocks. One of these slow blows feeds the fat white wire of the ignition switch. The ignition on position (green wire) feeds an eight position fuse block which I will use for the coils of relays - fuel pump etc. Having a starter contactor means that I don't need an always hot fat wire all the way back to the starter and I have jumpered the starter wire to the solenoid. I do have a wire to the alternator which will remain hot when the batt contactor is closed. It is protected from the battery by an ANL - basically a heavy slow blow fuse. My fuse blocks and relays are mounted on fold down panels in the center console with 1/4 turn fasteners so I can get at them easily if I need to along side the road. Oh I hope not! to quote Jose Jimenez when asked if that was a crash helmet he was carrying.

Thanks to all for advice on keep alive circuits. Those will be on the battery fuse block.

Ed

20230111_162232.jpg
Fuse blocks accessible in front of the seats.

20230111_180115.jpg
Contactors and slow blo buss

[lance corsi]

Bicyclist, we are using 2 relays, 150 amp, to deliver voltage to my two fuse blocks. One is brought on when the key is in the acc position, both on in run position. My buddy is doing the wiring, so can’t get into the weeds with you yet. We’re making our harness from scratch.

[lance corsi]

Bicyclops! Dang spellcheck!

[Bicyclops]

Bicyclist, we are using 2 relays, 150 amp, to deliver voltage to my two fuse blocks. One is brought on when the key is in the acc position, both on in run position. My buddy is doing the wiring, so can’t get into the weeds with you yet. We’re making our harness from scratch.

Roger that, Lance.

The weeds are getting pretty deep over here. ;-) There have been moments, and probably will be again, when I regret doing a from scratch harness until I look in the corner and see twenty pounds or so of rat's nest that isn't going onto the car. My friend who wires up interplanetary probes for JPL helped me out with the harness dissection and splicing up to the dieted engine harness. We'll just have to see how far along I can get before she's got time to help me figure out how to hook the rest of it back up. Power distribution I've got a pretty good handle on. The ECU? I'll have to take it one wire at a time.

I got my fuel pumps, relays, and pump controller all wired up today. I took Rob's advice and wired the pump relays to a switch for cranking without fire for oil pressure purposes. It's hidden so I can also use it for theft deterrence.

Ed

[Bob_n_Cincy]

This is how my ECU harness ended up looking.

ecu.jpg

The bundle on the far left goes to the front of the car. The rest go to the engine and transmission.

[aquillen]

I did some 24 signal carrying wires from the dash area back to the engine area for various signals including everything needed to work the stuff behind the driver including cruise, clutch, engine and trans signals. Then a 10 guage 12V fused from the front to back there. In the engine bay behind the driver is the ECU and TCM (with some tweaks it fools my 3.0 H6 ECM into thinking I have an automatic transaxle). All this runs along the left rail inside the body "sail". On top of the stack of ECM and TCM is a general purpose automotive relay and fuse box that handles all necessary power switching back there. Totally custom plan but still based on Subaru prints since it is after all still a Subaru setup with the OEM ECM, etc. No wires run in the center tunnel so I can pull the fuel tank without that fuss ( a connector setup would allow the same of course). But I'm really happy with this arrangement and it shows how few wires are really needed to make it all work front to back. There is another harness next to this stuff for the rear area lighting of course...