garrycol Posted April 22, 2019 Share Posted April 22, 2019 With a RV8 that is on carbs but ignition is being provided EDIS 8/MegaJolt (so no dizzy) and I wanted to replace the carbs with the 14CUX (Hotwire) injection system from a 3.9 V8, where would I take the ignition signal off the EDIS 8/MegaJolt system for the Hotwire ECU to operate? In the original setup 3.9 dizzy and coil arrangement, the Hotwire ECU would have taken the 12v B+ signal from the low tension side of the coil. I am not sure what is the equivalent is with EDIS 8/Megajolt. Not sure if it is relevant or not, but I have built this tach module to run my dash tacho and it works fine - so maybe this signal can be used for the Hotwire injection system - would seem to be the equivalent of the 12v B+ on an old style dizzy and coil. Tach_adapter_sch Advice gladly received 😍 - oh yes as has been discussed previously, MS is the way to go but please can we just stay with MJ at the moment. There will be a time before not too long when the MS3X questions will start in earnest, so please bear with me. Thanks Garry Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted April 22, 2019 Share Posted April 22, 2019 I'd go for the tacho signal, that's about what the ECU expects. Quote Link to comment Share on other sites More sharing options...
garrycol Posted April 22, 2019 Author Share Posted April 22, 2019 Thanks - that is what I thought but I was a bit unsure. Quote Link to comment Share on other sites More sharing options...
missingsid Posted April 23, 2019 Share Posted April 23, 2019 Just to add more supporting info. and just to join in! I run MJ and use the MJ output to jun my digital tacho circuit, it is not reliable at all revs so it would make sense to follow the above suggestion. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted April 24, 2019 Share Posted April 24, 2019 From memory (ten years ago) the above circuit without the resistors is what I used, and it worked fine. Later I put a switch which isolated two of the coils, which fooled the 14CUX into thinking that the engine was running at half the revs it was, hence it speeded up the tickover to about 1500rpm, useful for when using an aircon compressor for blowing up tyres... Quote Link to comment Share on other sites More sharing options...
zardos Posted April 24, 2019 Share Posted April 24, 2019 1 hour ago, ThreeSheds said: From memory (ten years ago) the above circuit without the resistors is what I used, and it worked fine. Later I put a switch which isolated two of the coils, which fooled the 14CUX into thinking that the engine was running at half the revs it was, hence it speeded up the tickover to about 1500rpm, useful for when using an aircon compressor for blowing up tyres... My 14CUX had an input (pin 33) from the aircon clutch which causes it to increase the tickover revs to better handle the load of the aircon pump when the aircon comes on. I'm note sure why you would want to do it a more complicated way Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 24, 2019 Share Posted April 24, 2019 I've used four 1N4001 plus a 5V zener and worked very well with the lucas ecu. No need for the resistors then. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted April 24, 2019 Share Posted April 24, 2019 19 minutes ago, Bowie69 said: I've used four 1N4001 plus a 5V zener and worked very well with the lucas ecu. No need for the resistors then. Ah yes! I forgot the zener! Sorry.... Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted April 24, 2019 Share Posted April 24, 2019 1 hour ago, zardos said: I'm note sure why you would want to do it a more complicated way Because I could! Also - I never thought about the aircon pin Also - how much extra revs does the aircon pin give? If the pump is under load I am thinking very little - my system causes the tickover revs to be (about) 1500rpm, and the 14CUX attempts to hold that ( by messing with the air bypass valve) even if it's put under load... It's complicated, sure - but fun Quote Link to comment Share on other sites More sharing options...
zardos Posted April 24, 2019 Share Posted April 24, 2019 From memory as mine was connected to a manual switch it would raise the idle by a couple of hundred rpm. Quote Link to comment Share on other sites More sharing options...
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