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Megajolt with 14CUX Hotwire


discomark10

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Thought this might be useful to some, so..

I finished my install of the MJ today and got it running with the distributor and coil providing the pulses for the 14CUX ECU.

I don't wish to run the dizy/coil in place so me and the old man (electronics wizard) set to finding out how to make the MJ provide the pulses.

We scoped the pulses from the dizy/coil and it seems to be getting about 75 volt spikes,

We put in some Zenor diodes limiting the voltage and come to the conclusion you need around 60+ volt spike every 2 seconds (at least) to get the ECU it to accept it.

1 coil earth (to EDIS8) on the MJ only seems to provide about 40 volts at a rate of about 2 a second, which is about half of the original dizy/coil voltage but enough frequency.

Going to try and make a voltage doubler circuit or similar to jump the 40 volts to around 80.

The other thing that I could do is use the EDIS8 tacho output and jump the voltage to around 75.

Cheers Mark

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What car/model is it ? My RRC 1990 when running on 14CUX gets absolutely no input from the distributor ?

Cheers

Michael

Yes it does, black/white wire from coil through AFM sub-loom, it goes via a resistor (I forget the value, 10K is it?) to the ECU, without this pulse the injectors will not fire fuel in.

It is a very common circuit to build for this, and other ECUs, just 4 1N4001 diodes from each of the ABCD on the EDIS plus a 5V Zener then to EUC, job done.

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Yes it does, black/white wire from coil through AFM sub-loom, it goes via a resistor (I forget the value, 10K is it?) to the ECU, without this pulse the injectors will not fire fuel in.

It is a very common circuit to build for this, and other ECUs, just 4 1N4001 diodes from each of the ABCD on the EDIS plus a 5V Zener then to EUC, job done.

I tried this, it only initiates the fuel relay at around a 60 volt spike. tried several lower voltages with now luck.

You not thinking about non alternator tacho?

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I half tried this as well before I swapped over injectors etc to run under full MS control, I didnt get it to work either, I didnt try too hard though. One thing that didnt quite make sense to me was using all 4 coils, wouldnt this double the number of pulses per cycle because of the wasted spark?

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I half tried this as well before I swapped over injectors etc to run under full MS control, I didnt get it to work either, I didnt try too hard though. One thing that didnt quite make sense to me was using all 4 coils, wouldnt this double the number of pulses per cycle because of the wasted spark?

its not so much about the amount of pulses. Testing it with the distributor by hand it runs the relays for about 2 secconds every pulse and at 500 RPMM your looking at about 16 pulses a second of 1 coil, I think that it must be due to the total lack of information about the internal workings of the ECU.

but it would work fine with too many pulses and running off all 4 would be the same as the distributor as its still 8 pulses per revolution.

we tried looking for a curcuit diagram for it with no avail.

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Aniesigh pretty sure that for the tacho (rev counter) which is a different wire but also happens to be white/black.

Ive measured the pulse from the dizy/coil and its around 75volts and a pulse below around 60volts does not allow it to work.

the zenor diode limits the voltage on the kit your talking about which is another thing to back up the reasoning it's not the same thing.

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They call it tacho driver but you use it for the black/white which goes to the ecu to give the pulses for injectors/fuel pump. There is no crank/cam sensor on the engine so that pulse is the only way the ecu knows the engine is turning over and at what rpm.

As I say, I have fitted megajolt to a 14cux and without the black white connected (tacho driver) it won't pulse the injectors or run the fuel pump

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They call it tacho driver but you use it for the black/white which goes to the ecu to give the pulses for injectors/fuel pump. There is no crank/cam sensor on the engine so that pulse is the only way the ecu knows the engine is turning over and at what rpm.

As I say, I have fitted megajolt to a 14cux and without the black white connected (tacho driver) it won't pulse the injectors or run the fuel pump

you may be right but why does mine and by the sounds of it, others who have posted not run on the lower votage.

And what about the 75 volts from the coil/dizy? Somethings not adding up. And on the flapper at least, it uses the same system with a voltage devider which also backs up the fact it needs the high voltage.

I think your right about it using it for the rpm.

when I turned the dizy with a drill it ran and seemed to run a bit better when I sped it up to a certain extent.

but I was more interested in getting it running in the first place.

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Maybe the tacho driver that was bought with the mj kit has more to it then? All I know was it has 4 wires going into it and one output, the small circuit was covered by heat shrink so couldn't see what is in it. Think I've got an email somewhere from the chap that supplied it about this, will have a hunt

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just found the emails from trigger wheels, in the standard setup theres a 6.8k ohm resistor between the coil and ecu, this gets removed when using the tacho driver they supply. maybe if this is left in (possibly in your case) the voltage is then too low at the ECU?

maybe find that resistor and remove it, then try seeing if the pump will prime with the lower voltage?

From memory the resistor was wrapped up in the loom not a million miles from the ecu

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just found the emails from trigger wheels, in the standard setup theres a 6.8k ohm resistor between the coil and ecu, this gets removed when using the tacho driver they supply. maybe if this is left in (possibly in your case) the voltage is then too low at the ECU?

maybe find that resistor and remove it, then try seeing if the pump will prime with the lower voltage?

From memory the resistor was wrapped up in the loom not a million miles from the ecu

Cheers that helps, ill try and have a look or even contact them, it may have even had a voltage doubler or similar in it, as you said it had more possibly.

I've tried with and without the resistor, we used an oscilloscope to measure it all each time.

EDIT:

Is this it on this page, 2nd item?

http://trigger-wheels.com/store/contents/en-uk/d58.html

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Putting this to one side for the moment.

Is anyone able to shed any light on why this MJ seems to run awfully bad.

its not the maf nor is it the ecu as I swaped them both out with the same results.

apologies for the 1st vid being upsude down.

You can hear it backfiring ect. Checked the plugs are on the right coil.

cheers mark

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Have you checked timing with a light? I'd put wires onto coil packs the wrong way round when i first wired the kit up that I fitted.

How's the ecu connected up at the minute? Still with the dizzy connected to provide the pulse or with the circuit you made?

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Have you checked timing with a light? I'd put wires onto coil packs the wrong way round when i first wired the kit up that I fitted.

How's the ecu connected up at the minute? Still with the dizzy connected to provide the pulse or with the circuit you made?

yea timing seems good. . I assume you do it from Clynder 1 right?

to be honest they are mirrored but I changed the points around to suit and I've checked it like 3 times.

itsrunning from the dizy atm, it doesn't time the fuelpulses fromt it does it.. if it does how do I time it?

Looks like the MAP hose is disconnected as MAP is pegged at 100kPa

it is.connected and does change as expected
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