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Megajolt on a 3.9 EFI - Muppet question


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For reasons of cost I am thinking of using Megajolt for bombproof ignition and leaving the standard EFI unit driving the injectors. Is this OK?

Sorry if this has been covered before, but I just spent an hour trawling though threads looking for the answer...


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If you are going to run EDIS then you may run into fuelling issues from the standard EFI setup…….

Two of us found that after sorting the ignition, the engine was running weak ….. in fact weak enough to induce weak misfire. We assume that this was down to the fact that dizzyless ignition give a much fatter spark and therefore the ‘burn’ was more complete.

Bothe of these were with flapper systems and both engine ran perfectly when later fuelled with MS.

Rather than the Megajolt ECU, I would suggest building a complete MS ECU, that way its easy to carry on down the fuelling road if you need to.



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IMHO you'd be missing a trick by not just fitting MegaSquirt and having done with it, but yes it will work fine.

To drive the coil feed to the stock ECU you need five diodes from the coil packs to the old coil -ve connection:

Many thanks for the excellent answers.

The reasons I am thinking of going the Megajolt route are twofold - one is cost, and the other is that it's rare that I run on petrol anyway, having an old and crude (but effective) LPG system on the car so it seems a waste to have the squirt bit and not use it.

Although it will be a while before I get the thing running again I wanted to make the decision (whether to do it at all) now while I have the rad out so I can sort the slotted disc and pickup bit of the job in relative comfort.

Thanks again for the help.


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  • 2 months later...


As I am thinking about doing the same thing, I need to ask a muppet question too.

My confusion is this. With the megajolt/megasquirt on ignition only, sending a reference back to the original ECU via the circuit shown by fridge will end up with 16 events per 720 cycle, unlike the orig rover one with 8 events per 720 cycle, because of the wasted spark system.

Have I got my facts straight, or is it just too late?


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