ItzDave's Megajolt thread!

[2ndGenGuy]

I'll have to look in my diagrams, but there is a wire on both the EDIS module and on the MegaJolt unit that have outputs for tach signal. It will run your tach, but for some reason it's not quite right to trigger the fuel pump relay. Somewhere, Cygnus has a diagram where you take the two negative wires off the coils and combine them using some sort of diode (zener diode maybe?) and feed that to your relay. I was lazy and just bypassed the relay and put my fuel pump on a switch. One of these days I'll switch it back...

[cygnus x-1]

anybody know what wire i hook the 'tach output' wire to, so my tach works. and any ideas to get the fuel pump going, other than running a switchable / 'hot' wire from the ignition.

Do you have the diode circuit hooked up? Along with the jumble of EDIS wires there was a thing that looks like a big wire splice with black heat shrink tubing around it. That's the diode circuit. There should be 4 wires coming out of it, 2 go to the negative leads on the coil, one goes to ground, and one goes to the tach/fuel pump circuit. On my Prelude the tach/fuel pump circuit used a blue wire that originally attached to the negative side of the ignition coil. Because the EDIS system has two coils you need the diode circuit to get a combined signal from both.

You may also be able to use the tach output on the MJL too. I discovered that the Megasquirt will drive the stock Prelude tach so theoretically it should work for you too. I'm not sure about the fuel pump since MS drives that separately but if you're using the stock FPR it should use the same signal as the tach.


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[cygnus x-1]

I'll have to look in my diagrams, but there is a wire on both the EDIS module and on the MegaJolt unit that have outputs for tach signal. It will run your tach, but for some reason it's not quite right to trigger the fuel pump relay. Somewhere, Cygnus has a diagram where you take the two negative wires off the coils and combine them using some sort of diode (zener diode maybe?) and feed that to your relay.

Ok, yeah. That's not surprising. Years ago I diagrammed the circuit inside the FPR and it was a bit strange. I never did figure out exactly how it was working but I know it was designed to use the signal directly off the coil.

Best bet then is to use the diode thing to run the tach and FPR together. I don't remember the wire colors for the diode circuit off the top of my head but if you have a picture of it I can tell you how to connect it.


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[itzdave]

vids... cuz it happened.

[cygnus x-1]

Cool man, you got it running! So what did you figure out with the fuel pump relay?


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[itzdave]

i hooked up the wire that i had goin to the coil, i think it was blue, to the 'tach out' from the MJ, and now the tach and the fuel pump work.

[jbabb]

how different would it be on an EFI model

[itzdave]

how different would it be on an EFI model

Megasquirt is for efi