What in the hell are those 3 relays on the driver's side fire wall? I'm cleaning up my engine bay for my motor swap and I'd really like to get rid of them...but not sure if they're necessary. I deleted the ECM and at least one of them appears to go to it.

I tried to use a wiring diagram but I'm just more lost now

 

One is fuel pump, the others should be MAF and MAF burnoff....IIRC.

 

Thanks. Key question then: If I'm keeping the mech fuel pump and OPSU, I can delete these relays, correct? The OPSU will run the fuel pump, and the rest are not needed, right?

 

 

What swap?
You need some way of operating the pump relay so the fuel pump will work

Most run a wire from the Ign switch to the Dk green/white wire at the pump relay so it powers up when the key is turned on

 

350 swap. From what I've been told the OPSU will power the fuel pump because they are wired redundantly (in parallel). By keeping the OPSU, I thought the relay could be removed, although it would be removing the redundancy

 

That would be my recommendation to simplify the system only some prefer to remove the OP switch and only use the relay.

 

OK cool. I'd personally prefer an OP switch on the back of the block to a big ugly relay on the firewall lol.

Thanks for the help, as always this site is fantastic

 

the only problem is the pump wont run till you start getting oil pressure which is fine if there is still fuel in the bowl, but if it hasent run in a while or the bowls are dry for what ever reason i can see you having to crank for a while to be able to fill the bowls. i dont know how long i just wired a switch to the relay.

 

Is this EFI or Carb? You said you deleted the ECM and being that your car is an 84 it was probably the CCC ECM. On the other hand, the three relays on the firewall normally came on EFI Cars, don't think a carb car has those relays. Also I don't think any carb cars came with an electric pump.
If this is an EFI motor, you will need the relay to prime the pump and pressurize the rails. If you don't, the car will never start.
If this is a carb motor, you still need the relay to bring fuel into the bowls. If they are dry, your car will never start. In both cases the OPSU will run the car, but not prime/start it.

 

It was a ccc. Now switching to a DP. The HO motors had a fuel pump in the tank. I'm also going to have a mech pump on the block. My main concern was that the in tank pump will run without the relay.

The oil pressure should come up fairly quickly when cranking. In my experience, unless you have just changed the oil and there is no oil in the system, it comes up almost immediately. The OPSU should trip the fuel pump once this happens.

Please correct me if I'm wrong, I'm just trying to make sense of this all.

 

My carb'd car has an in-tank fuel pump along with the mechanical one from factory.

 

It has an intank pump or a sending unit/pickup? I would have thought that it was just a pickup, no pump

If its a pump.....you learn something new everyday.

To the OP, why not do away with the intank altogether and use the block mount pump?

 

Yeah the HO cars in '84 have an intank pump and block pump. Vetteoz at some point in another thread told me it was better to leave it in to prevent vapor lock, etc.

So I'm keeping the in tank and mech pump. Besides, dropping the fuel tank looks like a PITA.

 

It's more of an electric low p.s.i. "pusher pump" to prevent vapor lock.

 

But as noted the pump still has to have time to pressurize the line and refill the carb bowls before you get any gas into the engine.
If you are removing the relay you still have to do something with the relay wiring?
If you were to install a push button under the hood on the existing pump wires, you could use it to run the pump to refill the system before cranking if the car has been siting a while

I believe the discussion was about the fact the in tank is not designed to have fuel drawn through it while it was un-powered; so it either has to be working or removed completely with a mech pump

 

I pulled all the loom yesterday. Realized I also have a fan relay up there. Since I have to leave that, I might as well leave the fuel pump relay too. What's the wiring schematic for it, bypassing the ECM wires? I read somewhere you have to jump the green ECM wire to a power source, not sure if that's true?

 

all the carb diagrams show no pump, but all the injected engines show green/white to pcm as being the control so this wire would have to be cut and instead of going to pcm it would go to a momentary switch with 12v hot on the other side of the switch. then you could use that to prime and once the engine is started or if it had been run you would just start it without messing with any thing

 

Couldn't this also be wired to the ignition so that no switch is necessary? And if that's the case, what wire would it need to be merged with? The wire that goes to the starter?

 

you dont want to do that really. the pump would be on all the time the key is on(regardless if engine is on or off), and you certainly dont want to hook it to the starter

 

So the advice would be to take the green wire, run it to a switch, and then to a power source?

Wouldn't the mech pump on the block need to be pumping for the fuel to get up to the carb, meaning that running a switch that would only be used to pump up fuel without the motor running would be pointless?

 

im not sure about that part, the factory did it that way for some reason, so basically you are just doing what the pcm did for you.

 

I would think the factory method would have been the ECM turned it on when the ignition was on. So in theory, that's probably the best method. There's gotta be a way to wire it so that it only gets power when the engine is running. To the alternator maybe? Not sure, I'm a MechE major and not a electrical major for a reason lol

 

Yeah nevermind that was dumb. Obviously if it's running it will have OP and then the OPSU will run the pump...

 

Trying to clean up everything under the hood and was wondering if I need these relay's or can I take them out? Doing a 383 swap.

 

Ccc ? If your going to a non ccc you can remove the baro sensor and esc.

 

That's what I was thinking but wanted to make sure before I removed them thank you.

 

I think the relay is for the fuel pump.