RamAirZ

Ok, I'm wiring up my new fuel pump in my 86'. I'm running new power/ground wires to the pump and running the relay supplied with the kit. Now, this setup calls for an on/off switch or ignition power so the pump runs with the ignition on, but I think I can use the stock ECM setup to cycle the pump. Here's a bad drawing of the stock relay (large drawing) and new aftermarket (small drawing)



K, the stock wiring goes like this:

Red=Fuel Pump Prime Connector
Orange= Hot at all times with inline fuse
Blk/White= Ground
Tan/Wht=Powers Pump (according to austin thirdgen, my diagram shows it going to the ecm but doesn't say what for)
Dk/Grn wht= Fuel pump prime, this wire becomes "hot" for a few seconds when I turn the key

My new relay says to do this (has new wiring harness with it):

red=not used
yellow= to fuelpump +
black= ground
blue=to battery + with inline fuse
wht= to on/off switch or ignition power

I'm thinking I can use this relay to serve the same purpose as the stock one based on the diagram, they look to work the same way. I'm thinking I should wire it this way

Stock Red=Red
Stock Orange= Yellow
Stock Black/wht=Black
Stock Tan/Wht=Blue
Stock DK GRN/WHT=White

What do you guys think? That basically goes against what the directions say to do with the new relay but it looks to work the same as the stock setup in design. What do you guys think? I'd like to get this wired up tonight

ternandes

iTrader: (7)

OK... the way that they are telling you to wire it is to have the fuel pump run constantly when the ignition key is ON.

You are correct in assuming that you can wire it the other way to retain the stock function, which IMHO is the way to go. The reason it is wired that way is because the only purpose for the relay is to prime the pump when there is no oil pressure, ie, right before the engine is started.

Once you have oil pressure, power is fed directly to the pump until oil pressure is lost. This is an important safety feature. If, for example, a fuel line were to rupture, the engine would stall, you would lose oil pressure, and the pump would stop. Powering the pump any time ignition is ON would cause the pump to continue to run, spilling fuel until either you emptied the tank or turned the key off.

Also, the stock configuration might save your engine if oil pressure were suddenly lost. Now, it's true that you could still run your fuel pump power through the oil pressure switch, but the stock wiring is doing the job, and doing it right. If it ain't broke...

RamAirZ

I posted this question on a few other forums and your the only one that understands what I'm trying to do lol. Everyone else basically suggests the "ignition on" method, which I don't want to do. Per my diagram, do you see any reason why this won't work? The new relay is a single pole double throw design. Will my idea work with this relay? I drew the diagram exactly how my manual shows for the stock relay and also what my new relay shows on the body of it. The symbol between the blk/wht-grn/wht is different on the stock diagram and my new relay (as in my pic) but is this just another way of saying the same thing? I want to retain the stock design with the oil pressure switch and cycle feature.

ternandes

iTrader: (7)

It will work. The stock relay is SPDT. The symbol is for the electromagnetic coil that throws the switch, in both diagrams.

BTW, is there something wrong with your relay? I am wondering why you don't just leave everything alone and just put the new pump in.

RamAirZ

I find these square relays all the time but sometimes the auto parts stores don't have the stock relay in the store. I figured I'd have a better chance at finding a replacement one day if I need it. That and my factory connector is broken so this will replace it

vetteoz

iTrader: (13)

Wrong
The OP switch for the pump is only there as a backup should the pump relay fail. Under normal operating conditions ,both the relay and OP switch are supplying power to the punp
Should the engine lose oil pressure, the fuel pump relay will still be suppling power to the pump allowing the engine to continue running.
If it worked as you state above ,in any case , at the 4psi setting of the switch your engine would be cactus before the switch operated to cut pump if you were running at revs and lost oil pressure

ternandes

iTrader: (7)

Yeah, they are fairly standard relays. You can use them as ON-ON or ON-OFF depending on how you wire them. BOSCH makes one that I have seen in all kinds of equipment. Wire your pump relay like the stock pump relay and you'll be fine.

vetteoz

iTrader: (13)

The instructions are probably for a carb car where the only source of power would be the ign or through a dedicated pump switch.
In your case the ECM is the "off/ on " switch they recommend so you just wire new relay as you outline above and everything will work like stock.
ECM will prime pump through relay for 2 sec; key on.Then when ECM sees the signal from the dist while cranking it will power up relay in parallel with the oil pressure switch so there are two sources of power to the pump

RamAirZ

Got it hooked up and works wonderfully, you hear the pump prime and shut off, car starts. Now just have to figure out why it starts, idles up and then stalls out. I was throwing a code 34 for the MAF before but it still ran, maybe the MAF is finally out?

ternandes

iTrader: (7)

My bad, I stand corrected. I was relying on a schematic from an aftermarket repair manual, which I should have known from past experience might be wrong.

I looked up some schematics online and discovered that vetteoz is correct. I apologize. In any case, though, I still prefer to stick to the original wiring.

RamAirZ

either way I get the priming feature this way, so I'm happy and it works, the fail safe to keep me driving if it goes out on the road is good too