Tachometric relay wiring query??

[Cozza]

G'day all

I'm installing a tachometric relay to control my electric fuel pump but I am not sure where is best to get the pulse signal from the ignition. I would like to connect it to the tachometer if possible just because i dont want to drag wires out into the engine bay. Now I realise the B/W wire at the tacho is feeding the +ve side of the coil and I'm not sure if this wire will send a pulsing signal to the relay.

I have a 4 wire tacho which I think is the current sensing type but I'm not sure and I don't understand how it works.

 

Anyone know where i can get a signal from inside the cabin? Or do I have to go to the -ve side of the coil?

Any help would be appreciated.

Mick

[Six_Shooter]

I'm not familiar with the device you are trying to connect, but if it is looking for a points trigger, and you have a 240Z, the only place you can grab the signal is from the coil negative connection. It's possible an adapter could be used to convert the current sensing that the tach uses to a points trigger, but in my eyes it way easier and less costly to simply run a wire out to the coil.

[d3c0y]

The stock tacho harness definitely has a wire that goes to the coil but i think it's the positive wire from memory so if you are using a CDI or some sort of high energy ignition make sure its not too much for your relay as it does burn out stock tachos.

 

 

I was looking at doing this too, what relay did you use and how much was it? Last time i got a quote from repco it was dear!

[RLY240]

Just run a new wire from coil -ve, you're going to need it anyway when you install your shift light / monster tach / FIA battery isolator!

Roger

 

[dazzed]

what does a tachometric fuel pump relay do ? I think you also need a different oil gauge sender unit , I think , what is all this for??

[benny]

what does a tachometric fuel pump relay do ? I think you also need a different oil gauge sender unit , I think , what is all this for??

 

 

in the event of an accident, the car should stall(hopefully) when this happens the relay would cut signal to the fuel pump.

[Six_Shooter]

 

in the event of an accident, the car should stall(hopefully) when this happens the relay would cut signal to the fuel pump.

 

If that's what it is for, there are better ways to do it, namely using an oil pressure safety switch.

[d3c0y]

How is that a better way to do it? You have to have an ugly switch hanging out the side of the engine plus run the wire through the engine bay?

[Cozza]

Hey Fellas thanks for all the input.

I am installing an electric fuel pump and have heard rumours that the original wiring is not quite up to the job of driving the pump and a relay is recommended. Therefore I thought why not put in an additional safety measure of the tachometric relay to stop the pump from running in the case of an accident (engine stall).

The relay I have is wired to the ignition switch (on position) as well as getting a pulse signal from the coil. This way the pump will run when the ignition is turned to on, for 2 seconds to prime the system and then again once the motor is running.

I have installed the relay beside the fuse box which is also close to the original fuel pump wiring. I will run a wire to the coil if necessary but would prefer not to have to tape a wire all the way there if I can avoid it.

Today I dummied it up using a long wire all the way to the coil (+ve side) just to see if it works. Turns out it does!! However I am still to test drive it, not confident yet but I have my fingers crossed.

Six_Shooter an oil pressure sensing method is perfectly acceptable although the wiring would be very similar, also it is not as common. Also I am not too keen on passing wires through the firewall if I can avoid it.

Will keep you updated on the progress but thanks again for all your input.

 

Cheers

Mick

[Cozza]

Well good news, a test drive suggests that the signal from the B/W wire at the tacho (supply to the +ve of the coil) is enough to trigger the relay. It seems to work fine.

 

I was looking at doing this too, what relay did you use and how much was it? Last time i got a quote from repco it was dear!

 

Hey Jake I used an AIROD gas safety switch about $15 from a local gas fitter, and then used a 40a relay behind that. Total cost was about $30 and an hour or 3 of my time. Not bad if you ask me.

 

I will post a pic or two tomorrow. Can't upload pics from my phone.

[d3c0y]

Awesome i will be doing the same, so pics would be great.

 

FWIW i run a carter rotary pump off the factory wiring with no relay at the moment and it works fine. I do plan on adding a relay to it in the near future.

[dat2kman]

Jake, the current draw on the Carter will be stretching the boundaries of the stock wiring, and may not be getting full amps. Better to run a dedicated wire with relay control to ensure as close to 100%.

 

i run ignition controlled tachymetric in the fuel injected race Z, i figure that if i get involved in a serious enough hit, ie loss of conciousness, and engine stall, i dont want a 60+ psi fuel fountain getting ignited if lines get torn etc.

I'm running an intank low press high vol lift pump to 2 litre surge, mounted under, then into a Bosch 44 pushing it up front, with a Malpasi reg on the return flow, back into surge pot, not ideal, as returned fuel is warm, but at least pot is kept full, with top o/flow back into main tank.

 

Prior to this setup it was getting inconsistent fuel flows, lean outs and bad surge through right hand corners, ie Qld Raceway and Lakeside!

[d3c0y]

Yeah i was thinking that, but i just googled it and it only pulls a pissy 1.5A max! It is a 4-6psi low pressure 72gph P4070.

 

I would be surprised if the factory wires couldn't handle that and the OEM option electric pump must have drawn about the same, which the wires were designed for.

 

[dazzed]

If that's what it is for, there are better ways to do it, namely using an oil pressure safety switch.

I thought thats what the idea was for ? its a good idea bit complicated much more simple ways to do it, with a 280zx oil sender if you loose oil pressure fuel pump stops ,but unless it is efi ,carbs will have to run out of fuel by this time damage to engine is done

[dazzed]

How is that a better way to do it? You have to have an ugly switch hanging out the side of the engine plus run the wire through the engine bay?

No you dont use a 280zx oil switch or Z31 look similar

[Six_Shooter]

How is that a better way to do it? You have to have an ugly switch hanging out the side of the engine plus run the wire through the engine bay?

 

The problem with monitoring ignition pulses, to run the fuel pump is that if for some reason oil pressure goes away (Oil pump pick falls off, leak bad enough to drain oil, that was not noticed, etc), the engine will continue to run, and damage, if not destroy the engine. When using oil pressure monitoring, it will cut fuel if the oil pressure drops below a certain point, which can be caused by a loss of oil or if the engine stalls for whatever reason, collision, electrical failure, etc.

 

I thought thats what the idea was for ? its a good idea bit complicated much more simple ways to do it, with a 280zx oil sender if you loose oil pressure fuel pump stops ,but unless it is efi ,carbs will have to run out of fuel by this time damage to engine is done

 

Yeah, unfortunately, carbs have this issue. An alternative would be to, instead of cutting supply for the fuel pump, to cut the supply for the ignition. I haven't tried this personally, but I can see it working. The only hitch would be if there was a long enough time in switching between the N.C. and N.O. contacts that cause the engine to stall at start up. A capacitor of appropriate size could correct for this, and only keep the ignition running milliseconds longer than it would without the capacitor.

[d3c0y]

For the record I have Webers, I wasnt thinking of injection.

[dazzed]

I think most tachometric relays are for efi and dont take a dirrect current from the ignition coil , a very low voltage from the ecu triggers the relay, as the relay has a electro magnetic coil inside you may find direct current from a points ignition may damage the relay or effect your ignition system operation at low speeds the relay could flicker to the point of failing, a relay only requires low voltage and amperage as low as 1.5 amps to activate it and are designed to switch on at 350 rpm an switch off at 350 or just below, you will have to run an additional wire from the starter side of the ignition switch  to activate the relay whilst cranking the engine,

[Cozza]

I think most tachometric relays are for efi and dont take a dirrect current from the ignition coil , a very low voltage from the ecu triggers the relay, as the relay has a electro magnetic coil inside you may find direct current from a points ignition may damage the relay or effect your ignition system operation at low speeds the relay could flicker to the point of failing, a relay only requires low voltage and amperage as low as 1.5 amps to activate it and are designed to switch on at 350 rpm an switch off at 350 or just below, you will have to run an additional wire from the starter side of the ignition switch  to activate the relay whilst cranking the engine,

 

Dazzed, I think you are right for ECU'd cars however, I'm not sure nut I think that for some racing governing bodies, a fuel safety device is needed irrelevant of fuel delivery method.

 

In regards to a pulse signal from the ignition, the research I have done shows most people use the -ve side of coil. I understand the -ve side of the coil has +12v most of the time (points closed) then switched to ground momentarily (points open). I can see that this is a definite signal change as it is grounded then not grounded. But, what I was attempting to achieve was reading the signal of change in current through the coil wiring. I figure there is a current draw only whilst the points are closed then the current momentarily stops while the points are open. So far it seems to be working. (I do have electronic ignition but it is the same principal)

 

Also, as the relay is connected in parallel to the ignition circuit it will only draw the current it needs to operate, not the current that the coil needs. The only thing I am worried about is the tacho not reading correctly as I think it is a current sensing tacho and as I am drawing slightly more current (to drive the tachometric relay) the tacho may be slightly out.

 

Not sure it is necessary to run the pump during cranking if you have carbs as hopefully the carbs will be full from the priming stage, Mind you this relay does only have a 2 second priming period which may be a little short so I may have to turn the key on and off a couple times, but I will find out soon enough.

 

Six_Shooter, you are right about engine protection but this is not what I was trying to achieve at the time. Might be worth thinking about cutting the ignition when you lose oil pressure though.

 

d3coy, I think Mallory recommend a 5a fuse for my fuel pump 4070LP. Also, I'm not sure if it is the wiring that was the problem with the original equipment or if it was switching/connections. I remember seeing a recall for the fuel pump kit from somewhere. Maybe in the workshop manual I downloaded from XenonS30

 

Here's is a couple pics of the relays I have installed as well as the signal wire I am using behind the tacho.

The relay on the right of the fuse box is the tachometric relay which activates the relay on the left, which is the main relay for powering the fuel pump. The gas fitter I bought the tachometric relay from recommended not to draw too much power through the tachometric relay hence 2 relays but cheaper than most other options out there.

 

Thanks again for your input Fellas

[dazzed]

Dazzed, I think you are right for ECU'd cars however, I'm not sure nut I think that for some racing governing bodies, a fuel safety device is needed irrelevant of fuel delivery method.

 

In regards to a pulse signal from the ignition, the research I have done shows most people use the -ve side of coil. I understand the -ve side of the coil has +12v most of the time (points closed) then switched to ground momentarily (points open). I can see that this is a definite signal change as it is grounded then not grounded. But, what I was attempting to achieve was reading the signal of change in current through the coil wiring. I figure there is a current draw only whilst the points are closed then the current momentarily stops while the points are open. So far it seems to be working. (I do have electronic ignition but it is the same principal)

 

Also, as the relay is connected in parallel to the ignition circuit it will only draw the current it needs to operate, not the current that the coil needs. The only thing I am worried about is the tacho not reading correctly as I think it is a current sensing tacho and as I am drawing slightly more current (to drive the tachometric relay) the tacho may be slightly out.

 

Not sure it is necessary to run the pump during cranking if you have carbs as hopefully the carbs will be full from the priming stage, Mind you this relay does only have a 2 second priming period which may be a little short so I may have to turn the key on and off a couple times, but I will find out soon enough.

 

Six_Shooter, you are right about engine protection but this is not what I was trying to achieve at the time. Might be worth thinking about cutting the ignition when you lose oil pressure though.

 

d3coy, I think Mallory recommend a 5a fuse for my fuel pump 4070LP. Also, I'm not sure if it is the wiring that was the problem with the original equipment or if it was switching/connections. I remember seeing a recall for the fuel pump kit from somewhere. Maybe in the workshop manual I downloaded from XenonS30

 

Here's is a couple pics of the relays I have installed as well as the signal wire I am using behind the tacho.

The relay on the right of the fuse box is the tachometric relay which activates the relay on the left, which is the main relay for powering the fuel pump. The gas fitter I bought the tachometric relay from recommended not to draw too much power through the tachometric relay hence 2 relays but cheaper than most other options out there.

 

Thanks again for your input Fellas

Yes thats right track cars running under cams regs must have this fitted but not many do, Cams released a diagram of a typical fuel pump cut out circuit and only 1 relay typical 12 volt relay that triggers of the starter and continues to run of oil sender unit no ignition came into it, you can also have a override switch that allows you to run pump without the engine running or a switch to deactivate the pump at an time, manual overide also acts as a theft device and if for some reason your carbs flood you can control the pump operation or when servicing or for any other fuel problem that may arise it is a simple operation and dont need wiring everywhere must be fused also and easy to diagnose if an electrical malfunction arises, zeds are simple so keep it simple, I your just running carbs the pump is only low pressure lucky if it draws 2 amps so not really required to run 2 relays those taco relays will easily run a intank pick up pump and a bosch high flow efi pump in one, which are mostly on volvo saab mercs beemas etc and most have around 8 to 10 pins on them for switching inputs so you can do quite a bit with them just need to know how the circuitry through the relay works some have an externall diagram ,240z and 260z tachos are very sensitive to pick up fields . and interference could effect its accuracy or even damage

[d3c0y]

I think most tachometric relays are for efi and dont take a dirrect current from the ignition coil , a very low voltage from the ecu triggers the relay, as the relay has a electro magnetic coil inside you may find direct current from a points ignition may damage the relay or effect your ignition system operation at low speeds the relay could flicker to the point of failing, a relay only requires low voltage and amperage as low as 1.5 amps to activate it and are designed to switch on at 350 rpm an switch off at 350 or just below, you will have to run an additional wire from the starter side of the ignition switch  to activate the relay whilst cranking the engine,

 

 

I'd be dubious as to it having enough current to damage the relay, as the stock tacho is inductive loop and would work on the same principal right? The only thing is if you run a CDI ignition you will fry it, because it fried my tacho :/