Fuel Pump Wiring idea

[awd92gsx]

OK....I don't like JTR's fuel pump wiring idea. It's a little antiquated (imho) and is very sparsely written (being borderline useless).

 

So...I've come up with my own little schematic and idea about how I'm going to wire my fuel pump.

 

I'm doing it this way for two reasons.

 

1) For simplicity reasons - other than one new wire running to the back of the car it should be easier to install.

 

2) Less parasitic/voltage drop across all circuits involved. If I understand JTR's system correct they are wanting you to power the fuel pump off of the black/white wire that goes to the HEI distributor. I don't like the idea of doing that. Also, running a thicker guage wire to the fuel pump will allow for less voltage drop across the wire which means more voltage makes it's way to the pump.

 

I'm probably trying to reengineer the wheel here...but, I thought I'd throw the idea out to you guys and get your opinions.

 

 

edit: the oil pressure switch is represented right after the 12v-switched (ign on) (black/white wire)

[DavyZ]

Uuuugh, it's been too long sinvce I last looked at the JTR manual, but didn't they do that for safety sake? I think the fuel pump should run only as long as the disty is spinning, if not fuel could (in certain circumstances) keep pumping into the motor---is this correct? I cannae remember anything, although being a post whore, I'll gladly add to the thread!

 

Davy

[awd92gsx]

Well, if I understand the JTR manual correctly (and without having an actual FSM in front of me) it looks like the BW (black and white) wire supplies the Dizzy with 12v switched (meaning it turns on/off with the key). I assume the BW wire went to the + side of the coil before...

 

Doing it the way I did in the schematic means the fuel pump will operate only when there is oil pressure or you are cranking the car over.

 

In the JTR manual it tells you to not connect the fuel pump system to the solenoid or it will cause the starter to operate when fuel pressure builds up. A simple diode placed in between the Starter Solenoid wire and the Relay keeps that from happening.

 

In all, besides the new fuel pump wire, there is only about 6 to 9 inches of wire needed for the entire setup.

[Guest Drive-ability]

The circuits look sound from here. I would make darn sure to use a good grade diode. There isn't a prime circuit however you can do it this way. I agree concerning it to the ignition system is not at all the way to go. One could always throw in a set of ford inertia switches for insurance. What fuel system is this targeted for?? HEI and a fuel pump could fit a carburetor or a fuel injection engine. The F/I engine has its own fuel pump circuits on board and doesn't seem complicated. The newer systems aren’t redundant as they mostly dropped the fuel pump oil pressure switch and use just a relay. That’s likely because of the computers and to save money.

[280zwitha383]

Sorry to rain on someone elses thread but is it not possible to just hook an actual switch up to the fuel pump. I'm not far from doing my swap and I'm trying to figure out the best way to wire the fuel pump also.

[awd92gsx]

280z,

 

Unfortunately you can't hook up a simple switch to the fuel pump. If you turn the switch on without the engine running it will keep pumping fuel into the carb, causing it to flood inside of your cylinders.

 

Drive,

 

Yeah, I've thought about the grade of the diode, too. What would be easiest is to find a relay that allows for to seperate controls to activate it. That way the two circuits are completely independant of each other. I haven't had much luck finding one, though.

 

Another thought I had would be to wire to seperate relays. One from the ignition and one from the starter solenoid wire. That way there's no possible chance of the circuit backfeeding.

[280zwitha383]

So, in my mind you would simply start cranking the engine, hit the switch to activate your fuel pump, and you should be good. When you want to stop the car you flip the switch off and turn off the ignition. Reguires a little coordination but sounds like sound basic plan. Am I wrong?

[awd92gsx]

In my fuel pump setup there is no switch to turn on the fuel pump...however, if one wanted to add a switch it would be as simple as running the ground from the relay to a switch and then controlling the relay ground.

[Guest tony78_280z]

Umm.. I bought an oil pressure shut off relay from carquest for like $11.00! it has three pins, + from ignition switch, - to fuel pump, and the third goes to the start selinoid, I assume to give juice to the fuel pump when the starter is spinning, then when the ignition switch takes over the juice comes from there. I never used this relay.

 

Instead what I did on my 280z... There is a 5th unused pin on the ignitions switch. (Why the manufacturers put this pin in there and not use it is beyond me.) After testing with a test light, I discovered this 5th pin has power when the car is in the start position just as the pin for the starter selinoid. (If you simply splice the starter selinoid's pin into the the run position, the starter will keep turning even after the car starts.) I spliced this newly discovered 5th starter pin to the run pin on the switch to give juice to (basically everything) the dizzy and the fuel pump when the ignition switch is in either the start, or run position. This is not particularly safe as should the car burst into flames it would continue to shoot gas until the key is turned to the off position, or it exploeds with enough force to sever the wire.

 

Then I scrapped the whole thing to go with a mechanical pump. Anyone want the left over parts? Fuel pump, relay, and pressure regulator. Has less than 500 miles on the whole set up. =)

[2126]

280z' date='

 

Unfortunately you can't hook up a simple switch to the fuel pump. If you turn the switch on without the engine running it will keep pumping fuel into the carb, causing it to flood inside of your cylinders.

 

Drive,

 

Yeah, I've thought about the grade of the diode, too. What would be easiest is to find a relay that allows for to seperate controls to activate it. That way the two circuits are completely independant of each other. I haven't had much luck finding one, though.

 

Another thought I had would be to wire to seperate relays. One from the ignition and one from the starter solenoid wire. That way there's no possible chance of the circuit backfeeding.[/quote']

 

Sorry but I have to disagree with your statement about turning on a fuel pump without the engine running and causing it to flood inside the cylinders!

That could happen if the needle and seats on carbs are shot or you are just running too much fuel pressure. I have my system setup this way and it is working perfectly. Of course there other details involved.

[awd92gsx]

Would you want to leave your pump running with the engine shut off?

 

Besides, it is also a safety feature. It's generally safer to have the fuel pump shut off with the engine

 

I personally see no reason to have to toggle a fuel pump with a switch (unless you are using the switch for security purposes) as it has no advantages...unless I'm just not seeing them.

 

Could you explain why you have yours wired that way for me?