Hi Guys,
Ive just started to wire up my fuel pump through megasquirt, rather than using the supplied ignition live wire that comes in the PWS loom pack.
I checked the polarity, and it seems to be switched earth - 12v permanently, and the prime pulse is 8v, then returns to 12v until the engine is started - Bearing in mind the pump is a 12v pump, how do I wire it in?

It was working fine before, But thought the cut feature was a good idea?

I can't get my head around why people use switched live, to me, it seems more complicated, using more wires than a switched live circuit would?

Im confused....

Thanks

Tom

Figured out that the MS output is 4.5v switched earth, But I'm now looking for a relay with a solenoid of 4.5v operating voltage.

If anyone can tell me how to identify the characteristics of a relay, or point me in the direction of a 4.5v one, I'd be very grateful

Tom

i think you measue 8,5 volts because the pulse is to short for your equipemnt.

also 4,5volts should be a 4volts relais..

but i think that the relais output from megasquirt should switch to ground..

and then you could use an normal ordinairy relais...

also you only need one transistor and one resistor to archive this with a Microcontroller sow bloody easy task.!

Tks

The output from MS is a switched earth, all you need to do is put a permanent live to 86 on your relay and connect MS Fuel pump output (pin 37) to 85 on your relay

This would then switch 30 and 87 to CLOSED. So a fused (say 10A) permanent live to 30 and 87 goes to your fuel pump +12v

You only need a 12v relay, either of these would suffice

http://www.vehicle-wiring-products.co.uk/VWPweb2000/relays/relays.html

either R20B or MR25 if you want the smaller type. (I'm using the MR25 - works a treat)

MS runs the fuel pump initially on startup then stops until engine cranking starts.

Hope that helps


[Edited on 16/7/06 by darrens]

[Edited on 16/7/06 by darrens]

[Edited on 16/7/06 by darrens]

[Edited on 16/7/06 by darrens]

[Edited on 16/7/06 by darrens]

[Edited on 16/7/06 by darrens]

Cheers chaps, I have been spending all evening trying to sort it all out. I`ll pop down the motor factors on tues to get me a relay and in line fuse i think - It`s really been doing my head in!

Much appreciated

Tom

I have just tried what darren suggested using a sierra relay (the same as the headlight (main and dip) relay, and...

when ign is off, the pump works slowly, (and the oil warning light is dim)

when you turn the ign to position 3, the pump goes off (and the oil light is bright)

I cant start the car as parents are off on hol early tomorrow, so theyre in bed.

I am aware there are Normally open relays, and normally closed, but i'm not sure which the sierra one is - possibly the wrong one.

However, after a few seconds, the pump does not start running (indicating the relay is the wrong type)...

Arrrrggggghhh

Tom,

I do apologise, just spotted my mistake

You fuel pump and MS supply needs to come a from a ignition switched supply that isn't interupted during cranking.

Not sure why your getting a slow running pump (shouldn't run at all until power is on MS).

The pump should only run when power is applied to MS (runs initially on startup for about 4-5secs)

If your wiring as shown below, everything should correct.

[Edited on 16/7/06 by darrens]
Rescued attachment v3ext_wiring.gif