fuel cut off circuit -- wiring question

I have a problem with my XJ flooding out on cold mornings. The engine is a 4.6 stroker running 30lb injectors. The cold weather starting fuel curve is too rich with the big injectors. It runs fine otherwise.

I'm f'n tired of pulling the fuel relay every cold morning to get the motor to start if it takes a notion to down itself.

I plan on installing a fuel cut out in line to the pump. The interrupt is going to be aft of the ballast and ballast bypass relay. In other words, it will be in the main power supply wire to the pump. I will be using a double throw relay with the 87A terminal powering a red LED to alert me to the “pump off” status ("oops" prevention if you will).

My question is, can I power the switched 86 terminal off the pump's power wire that will be feeding the 30 terminal as well, or would it be better to power the 86 terminal from the ignition switch directly?



Thanks,

Bones :skull1:

You could power the switch from terminal 30. Depending where the relay is located, I would rather take from from 'somewhere' close to the switch -- saves running one wire to the relay from the switch.

Also, maybe used a switch with a built-in 12V indicator, rather than wiring it to 87.

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If you want to have the switch/relay cut power to the pump, you need to use contacts 30 and 87a.

In my original plan, the switch was designed to be normally closed for fuel pump operation, so power to the pump should be on the 87 terminal out.

However, I can see benefit in wiring to the 87A (in a switch normally open method). Then I could use a switch with a built in LED to signal pump off status and save routing the separate LED.

I'll have to consider this set up in relation to where I can mount the toggle.

Thanks,
Bones :skull1:

How about just using an SPDT switch? Put in inline with the signal supply on the relay, with one position going to "light" the relay and the other to "light" a pilot for you? No additional relays, little additional wiring, and alles gut, nein? Leastways, that's how I'd do it.

Results?
Switch "ON" - normal function
Switch "OFF" - relay not supplied, indicator for pilot "ON"

That's just off the top of my head, so I don't know which relay terminal to hit offhand. However, the fuel pump relay is supplied with key ON (IIRC) so it should make no odds otherwise.

5-90

Are you just trying to turn the pump off sometimes?

Why not just put a switch in line to the fuel pump, open/close??????

Maybe I'm missing something here? Strocker=bad???????????



hinkley

5-90 said:

How about just using an SPDT switch? Put in inline with the signal supply on the relay, with one position going to "light" the relay and the other to "light" a pilot for you? No additional relays, little additional wiring, and alles gut, nein? Leastways, that's how I'd do it.

Results?
Switch "ON" - normal function
Switch "OFF" - relay not supplied, indicator for pilot "ON"

That's just off the top of my head, so I don't know which relay terminal to hit offhand. However, the fuel pump relay is supplied with key ON (IIRC) so it should make no odds otherwise.

5-90

Click to expand...

5-90 beat me to it. A relay is one more thing to fail, and you need a toggle switch to control the relay anyway, so why not just make it a SPDT toggle and eliminate the relay? Just get a heavy duty switch that will handle the amperage of the fuel pump.

For any moderate to heavy load I think a relay can handle the power more reliably than a switch alone. I also think a relay has the advantage of not increasing the length of wire the power has to flow through to run the pump. If I wire the pump to run through a double throw relay on the 87A terminal there are no moving parts unless the switch is activated.

It also allows me to use any switch I choose both for stealth and aesthetics (yea, bite me; I like my junk to work AND look good. It's a neat concept Hinkly, you should look into it ).
The stealth part will allow it to be used as a theft deterrent also.

Bones :skull1:

I was looking at this from a security perspective aswell.

Using just a switch to interrupt the power to the pump(DG/RD in kick panel) is a clean solution provided that the switch is up to the task.

From what I've measured and read, it looks like the pump will draw 2.5 to 5 Amps. To be safe, I would use a switch rated for 10 Amps.....or a relay. Beware of current ratings on cheap switches.

The guage of the DG/RD wire is 14 AWG.

Eagle, you usually catch on so well...

My idea wasn't to break the power line to the fuel pump, but to break the relay "trip" signal with the switch. This would offer a load to the switch probably measured in milliamperes, rather than switching the probably 10-12 amperes - which was the reason for the OEM relay in the first place.

I'm all for using a relay where necessary to enhance the longevity of a switch, but you just don't need it here. By switching the "trip" line back and forth (and I'd use an LED with a current-limiting resistor for the pilot light) you have a milliamp load to deal with and your wiring is much simplified.

I don't have any trouble doing electrical mods, but I like to make them a simple as possible and keep the use of actual wire to a minimum...

5-90

Eagle said:

5-90 beat me to it. A relay is one more thing to fail, and you need a toggle switch to control the relay anyway, so why not just make it a SPDT toggle and eliminate the relay? Just get a heavy duty switch that will handle the amperage of the fuel pump.

Click to expand...