RS Motorsport :: Classic Speed Restored

Hey,

Hi guys. Just finished rewiring my car and amongst other things I fitted a safety switch used in LPG setups. The tacho signal is being directly received from a Crane Hi-6 unit (green wire) then on to the Tacho. The Tacho works but the safety switch is not being activated. Any clue as to why? I've had to temporarily bypass it to get the fuel pump working.

Apparently the signal reqiured is a square wave signal, and it usually operates off the negative side of the coil. The tacho output by the Hi-6 does this so unsure of why its not working. Its a straight wire from the Hi-6 to the relay.

Hi,

those LPG relays are meant to be used with a normal (inductive) ignition; the Hi-6 is a capacitive discharge ignition and connecting anything else (tacho, this relay) to the coil itself is a nono.
The relay 'senses' the voltage-spikes normally seen at the - side of the coil.
Inside the box is an inline zenerdiode (anything between 30 and 60 volts usually).
If you can open the box bypass that zenerdiode and try again.
Or alternatively you can create your own 'voltage-spark' by using the tacho-output to switch on/off a transistor with a small coil (old realy) as a load.

Can make a drawing if you want and send it to Roger M so he can post it here.

Regards, Leon.

Is this box intended to cut the power to the fuel pumps if no current is detected from the coil i.e. the motor is not turning??

I need to put some sort of safety cutout on the pumps in my car to meet the regs and this sounds a decent solution (when working).

the solution I am using is a tachometric relay, the one I have is a Bosch unit

I do know people who use a LPG relay as well with the same effect but have a bypass button to prime the fuel pump / carbies before starting

Sounds like it would be easier just to use an oil pressure switch.

Yes this is exactly what's it's for.

I was originally going to use a tachometric relay but there aren't any wreckers here in Perth that let you look around or any that have a JB Camira or Vk Commodore. Not sure of what else have them. Went and found a new BMW Bosch unit and nearly died when I was quoted $275 so I decided to go down this route.

Unfortunately you can't tap from the negative side of my new Crane LX92 because it's operating at around 500v!

I genuinely can't figure out why the Tacho will work on the same but longer wire thats from the Crane Hi-6 than the relay is. It's really odd.

This unit is perfect for anyone with a normal coil.

Any other suggestions?

Anyone have a tachometric relay for a decent price?

The benefit of this setup over an oil pressure switch is that it self primes briefly when activated and turns off immediately on loss of engine running signal. An oil pressure switch would potentially have pressure in it for a while after a crash and doesn't self prime the pump before turnover.

Awesome I wasn't quite sure what I'd bypass it with but now I know (1 kohm resistor) I'll report back.

If this works then I reckon this would be a great safety fix for on the road and race cars requiring CAMS approval.

I am getting a little lost. These relays used on LPG setups are different from a tachometric relay? Either will work on a standard 1970's Escort ignition system/coil (ie no need to by-pass anything)??

And,

if the ignition is ON but the motor is not turning, does it still cut power to the pumps?

Some great information above....

I picked this idea from a mate who quite often comes up with these simple fixes. I used the alternator wire to dash as the trigger for pump cut off. if the light comes on from either engine stop due to "incident" or even if the fan belt brakes no power to pumps. The Alternator light is connected to a lighting relay which is then connected throu to pumps. If the Alt light comes on for what ever reason it powers relay to disconnect power to pumps. If you need to prime system before start install a switched bypass to a 2 step starter button. 1st step Prime, 2nd step Start. All quite simple without overthinking and costs about $20.

Mik

Ill try and find the wiring diagram if anyones interested

Ok Miniliteman. Now what?

Probably a bit late to add info, but I just wired my electric fuel pump through a new twin male connection oil pressure gauge i.e. NO oil pressure = NO fuel.
Protects engine on start up, especially if it only gets started occassionally like mine and in case of a roll over, petrol supply is cut.

Thanks Leon. I googled what a Zenerdiode looks like, and as you say it's the clear orange and black thing which is below the "this" I marked. It's second inline. I can take it out and solder in something else easily enough. However you've mentioned a few options. A wire, a 1 kohm resistor, a 10 kohm resistor. Which one?

The whole unit was covered in a black plasticy rubber compound to make it waterproof. It took ages to pick it all off! Many thanks for your help so far.

I have decided to use a Holley Blue fuel pump/regulator but am also looking at the Holley fuel safety switch P/N 12-810. It appears to cut power to the fuel pump if there is no oil pressure but also switches the pump on when the starter circuit is powered. Sounds like a good solution to me...

www.holley.com/data/Products/Technical/ ... 0-1rev.pdf

Just curious, what happens if you crash and your engine keeps running?? Not all crashes cause an engine to stop.

An inertia switch will cut out and make the engine/fuel stop if wired correctly. If you're worried about it going off accidentally, put it within reach so you can reset it.

The general thinking there is that if the engine continues to run then the fuel pipes are probably intake. If they were split then possibly the engine would starve of fuel and stall.

I guess an accident could easily result in split fuel with the engine running resulting in possible fire. How far do we go with safety?? Killing the fuel pumps when the engine stalls is a requirement of our (and probably your) regs but theose regs dont seem to worry about accidents involving unconcious occupants and the engine running and fuel spills.........