ok clever people,ive got just 1 problem with my ms unit now.
the output that fires the pump relay is only showing 5 volts,its not enough to fire the 12v relay,any ideas?

The fuel pump output is a pull-down output, so it grounds one side of the fuelpump relays coil. The other side needs to be connected to a (switched!) 12V

Maybe the fuel pump transistor is knackered then, Conrod?

Asked on the MS forum for you - there's no setting in software for the inverting the fuel pump, so it *must* be something up with the unit itself.

Chris

IIRC the output is to earth the switching side of the relay which should be live fed from the main ignition relay. The switched side is then fed from the battery through a fused connection and this is permanently wired to earth.

I will send you my wiring diagram if you let me have an email address.

Regards,

Steve

SEBASTIAN SAID....The fuel pump output is a pull-down output, so it grounds one side of the fuelpump relays coil. The other side needs to be connected to a (switched!) 12V



unfortunately on mine it supplies a + 5 volt for some reason.,tranny WAS replaced Chris,,any ides if i can get a 5 volt relay to fire the pump relay?

Tango,ive got a diagram thanks,i didnt build this unit so dont know is something has been done wrong

I suspect it may just be something else backfeeding down your earth, as the same has been found lots of times with the injector switching wires.

Folk often think this is a problem when it is how they are.

Hopefully you don't have a problem.

hm,backfeed could be a possibility,but its timing (2 secs or so) is correct.
ill have a play and rewire the relay morra

I'll pop over one night and take a look if you like Johnski? Everything looked ok when I had it apart here at the weekend.

Chris

cheers christof

quote:

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Originally posted by theconrodkid
unfortunately on mine it supplies a + 5 volt for some reason.,tranny WAS replaced Chris,,any ides if i can get a 5 volt relay to fire the pump relay?

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I have a feeling its V2.2 but i'm sure john will clarify later

yup,it says V2.2 on the pcb,just tried the back feed theory and its a no go.
still getting + 5v at that terminal for the pump prime period and when the engine in running

What does it do when it's not at 5v (i.e. after the prime period, but before you start cranking)?

You need to check D7 is a) the correct component (1N4001 diode) and b) the right way round.

To verify, check the voltage at each end of the diode, you should get 12v at both ends. If you get 12v one side and 5v the other then this is your problem.

One end of the diode is connected directly to 12 volts and the other goes through a transistor and then to the relay. When the transistor receives a signal from the processor it closes the circuit and you should get 12v at the output.

I think D7 is a zener diode which means it clamps any voltage going through it the 'wrong' way to a specific voltage (in your case 5 ish). If the diode is wrong then you will only see the 5 v at the other side instead of the full 12.

[Edited on 7/6/07 by matt_claydon]

The 1N4001 is just a simple rectifer, not a zener, so if it were fitted backwards the relay output would have ~12v continuously, and transistor Q3 would be dead a couple of milliseconds after switching on. It's quite possible a zener has been fitted accidently of course, but that should be easy to identify as 1N4001's have the code marked quite clearly on the body.

One thought: the Base-Emitter junction of an NPN transistor like Q3 acts like a ~5v zener if reversed biased, so make absolutely sure the transistor has been fitted to the PCB correctly.

cheers for your replies peeps,looks like a job for superchris

d7 and q3 are both the right way round.
voltages are 11.5 and 10.7 on d7,but with wire to pump relay disconnected the voltage at d7 drops to 00.2
ohms are 1.68m and 3.o4m ohms depending on what way round the leads are....any help?

Are you sure that the output transistor has not been damaged ? it could have been connected directly to 12v or fuel pump with no relay? if so it may be supply ing a 5v output when measured with a meter but at probably very low current due to leakage, instead of conducting the supllied 12v to earth.
Paul.

output tranny was replaced just in case,its always had a relay in the circuit.oh well

Sorry John, am at a loss as to what the problem could be if you've replaced the components and it's still not working. Top right diagram of Page 3 of this PDF shows the circuit and where is should connect: http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf all I can suggest is that you check all the components are connected externally and to each other correctly. Otherwise I think you need someone good with electronics to look at it in the flesh!

Good luck

One thing I forgot to mention, some automotive relays have a built in diode to suppress the back EMF when the relay is opened. If such a relay is connected backwards, it will appear as a virtual short circuit to the relay driver transistor.

If your relay is of this type, the Megasquirt output MUST be connected to the correct side of the relay coil. From a relay I have to hand this would be pin 86 of the relay, and pin 85 should go to your switched ignition supply. However, I think this can vary so check polarity on yours, switched ignition supply must go to 'bar' side of diode.

Apart from that I'm running out of ideas. Does the relay operate if you ground the fuel pump relay output pin of the Megasquirt? (this will not damage the MS if it has been built properly since it's an open collector output).


[Edited on 12/6/07 by MikeRJ]

its only a cheapie relay Mike,its only putting out 5 volts so wont fire the relay,thats the main prob,ive mailed my tame electronics guru and am waiting for a reply,ill let you know if we find anything.cheers John.

The megasquirt doesnt put out any voltage it just connects the relay coil to ground.The other end of the relay should be connected to +12v and if you connect a wire from the pump output pin on the relay to the chassis it should pull in the relay.you may be following a false lead by thinking the output should be 12v as it should not read anything when energised and may show a voltage on a volt meter when not energised .It should show 12v when the relay is connected and ready to operate though , if it is all connected and still only showing 5v then it looks as if the relay or its connection to 12v is faulty.
Paul.

quote:

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Originally posted by theconrodkid
its only a cheapie relay Mike,its only putting out 5 volts so wont fire the relay,thats the main prob,ive mailed my tame electronics guru and am waiting for a reply,ill let you know if we find anything.cheers John.

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