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Evolution55

Tacho feed

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Hi there I am currently in the process of fitting a G4 EVO 1-3 plug and play ecu. We have an expansion loom fitted and are fitting additional sensors etc and have changed ignition from wasted spark to sequential as i am running coil on plug. The issue we have is having a tacho output so the factory tacho works as it would get its feed off the stock ignitor, but we dont have any outputs/inputs left other than ecu hold power. Will it cause an issue using this output? Or is there another way?

 

Cheers

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The hold power will have additional circuitry which will cause issues when trying to use a tacho.

Also the tacho I suspect will be looking for a high level signal (coil negative type) so the ECU wouldn't drive with out it being modified. 

 

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I have an Evo 2 that I have converted to coil on plug, and the tacho dont need high level signal. It will work with an aux-output setup as Tacho like most "newer" cars do. The plugin ecu should already have a tacho output taken care of. I assume you are using the plugin ecu for an Evo 1-3 vehicle?

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Its not the fact that i have changed to COP but that we've used extra outputs to change from wasted spark to sequential. We've run out of outputs for the tacho.

Does the ecu hold power output need to be powered up or earthed for the ecu to power up?

Cant get the ecu to power up to connect to a laptop.  The fuel pump primes and theres 12v to the coils but theres only 3.4v going to the ecu and 3.4v at the injectors.

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Sounds like you have a damaged wire somewhere - could be 12v or ground side though. Or your ECU isnt grounding the main relay enable pin, and so you are just reading the small amount of voltage running backwards through the ECU or some other device.

Things I would rule out from your description so far

1) flat battery - if you get 12v anywhere, your battery can clearly supply this much

2) possible but unlikely - you have something connected that is causing a partial short to ground - if you have this big of a short, your fuse should have popped already.

First thing, get a wiring diagram as you need to figure out where the injector 12v feed differs from the coil feed. 

heres one that showed up on google and looks legit https://www.workshopservicemanual.com/m007256-mitsubishi-lancer-evolution-3-ce9a-1995-1996.html 
 

I have no idea where you've powered your coils from, but if those have 12v then you can rule out a wiring issue on the path between them and the battery - so at the point this path joins the "normal" path to other systems, you know those are also good from that point back to the battery. Looking at the factory manual, all the other systems you have mentioned are powered from the MPI control relay, and before that its just a fusible link to the battery. I'd start by locating this relay and checking that you have 12v coming in and going out of it. If you have good input but bad output, remember that the relay has to see ground on pin6 to turn on - normally this comes from the ECU but as a test, disconnect the ECU & try grounding from the main relay enable pin in the wiring harness to somewhere on the chassis to enable the relay, then test again - this tells you if its a power wiring problem or a "ECU isnt grounding the control wire for some reason" problem. If its got good output with the ECU connected, test again at every point you can get to that should be "downstream" of this - injector connectors, , and just to be sure, unplug anything you find connected along the way - injectors, EGR valve, idle air valve, etc.

To verify the ground side, run a temporary wire straight from the engine block to the ground pin on the ECU and see if things improve. I doubt it will but you need to rule it out. Also, with the key on (to generate some load), set you multimeter to Volts and connect it between battery negative & the engine block, it should read <0.25v. if its reading anything substantial, you have a grounding issue between battery & engine.

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