Megajolt & Fuel Pumps
Turbo Mini Forums

I've had a search, but can't find anything specific about what I'm thinking about.

In my clubby, I'm going to be running an SPi tank & pump with a filter king to get the fuel preasure right and megajolt for the spark.

I have noticed that there are 4 programable outputs on the MJ units.

Could I program one of these outputs to trigger the relay that will power the pump?

I'm trying to find an efficient way of only running the fuel pump when the engine is turning/should be running and this seems like a good idea.

Does anybody else do it this way? Has anybody got a better idea/siolution? I don't really want the pump running if I have the ignition on and the engine off.

should work,

failing that you can connect a relay to the oil pressure switch.

Thanks.

If I used the oil preasure switch wire would that not just give power when there's oil preasure (oil presure = completed circuit??)? Or have I got that completly wronng?

It's a good idea, it would be standard with a full EMS.

There's a thread on using a very common relay from early EMSs here if you want a more basic solution.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=247462

Schrödinger's cat - so which one am I ???

Escort XR3i fuel pump relay now on my shopping list

If something is worth doing, it's worth doing half of.

That's a good thread. Thanks

Does the inertia swtich just go inline between the relay and the pump? I'm guessing I can use one from any car as long as it's 12v.

Schrödinger's cat - so which one am I ???

I like scrappys and I keep meaning to find an excuse to go to one...

Found a few on ebay £10 - £12 seems the norm.

Need to get the Ford EDIS stuff too, so I think a visit is in order one Saturday morning.

Thanks for everybody's help and advice, much appreciated!

Would I be better putting the inertia switch before the power to the MJ (with the MJ controlling the pump)? That way it kills spark and fuel if/when I have a bump?

wouldnt hurt,

on a FI car cutting the pump would stop the engine in just a few secs, but with an su and a float full of juice....

Makes sense to me!

If something is worth doing, it's worth doing half of.

Schrödinger's cat - so which one am I ???

Maybe another use for one of the other programable outputs...

Doesn't switching the ignition off kill the power instantly, in the same way an inertia switch would?

Good point. I would like to kill the engine instantly in the event of a bump and not leave it running the float bowl out.

If something is worth doing, it's worth doing half of.

I would say so. Looking at the diagrams on here, you just have the 2 +ive wires from a switched live fuse. If the ignition goes of, power get's cut to the MJ. Inertia switch should do exactly the same thing, but with a bump instead of the key...

whats wrong with just putting the bump switch on the powder feed to the pump??
have i missed something??

My plan for the wiring was to take a fair sized wire from the fuse box on a switched live circuit to power the relay box (daisy chained between the relays). It sounds like this wire is the best place to put the inertia switch.

Relays will run the following:

MJ unit, switched on the ignition.
Fuel Pump, switched by the MJ programable output.
Super Charger clutch, again switched by the MJ output.
Front mounted radiator fan (kenlowe type thing), switched by the switch in the rad.

Leaving a couple of spare slots for what ever I've missed.

There's still plenty of fuel in the carb float bowl and fuel lines, so I'm looking at stopping ellectircal stuff which could make a spark and a resulting big bang

My point was (and remains) that inertia switches were "invented" to shut down high pressure fuel pumps in the event of an accident to stop fuel being sprayed around at high pressure.

They aren't rated to carry the current for all the rest of the electrics on a car and they probably don't switch very cleanly (electrically) if operated above their rated current.

The rest of the electrics on a car, in an accident, rarely create a "spark" resulting in a "big bang" - they simply get shorted out and the massive current capacity in the battery leads to an electrical fire from the short circuit. Those kind of electrical fires will occur whether you have an impact switch or not, and irrespective of what it controls.

I can't say I'm familiar with MJ, I've only worked with full EMSs, but I've never seen a factory EMS with its main power feed through an impact switch. Most have a permanent power feed and an ignition input to instruct them to power up. Megasquirt, at the cheapest end of the spectrum, (which I am installing) only has a single feed but even it has to be through a relay, not an impact switch. If MJ just has a single ignition feed then, yes, its circuirty and CPU is designed to accept being switched on and off at random and should not suffer if you put the impact switch in series too.

But, if you really want to kill all your electrics through the impact switch, you are going to need relays because the impact switch will only be rated for the fuel pump current, and not everything else as well.

As for "plenty of fuel in the carb float bowl", remember there is an awful lot more in the petrol tank !!!

Schrödinger's cat - so which one am I ???

Sounds like I just need to kill the tank then, as killing the rest of the ellectrics might not work and may well just kill the switch etc.

Thanks for you're advice.

That's fine as long as you're engine stops and you're oil preasure drops....

That's why we have an inertia switch too :)