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Ongoing ECU issue, HT leads advice, one for Jonny H?


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Evening all. Long story short, my 3.4 twin plug from 3.2 conversion with Canems ECU still will not run right. While on the rolling road at Lloyds specialist developments (a long time ago) a possible cause was cited as my original HT leads. We got around the problem and I drove it home. At the same time as fixing an air lead I made myself a new set of HT leads using good quality cable, crimped on connectors and original distributor ends and resistive plug caps (3k ohm ). A mate has lent me a book by the guys who runs Lloyds, Dan and Nathan and in it they highly recommend resistive HT leads to suppress interference.

So, to my question; Are non-resistive HT leads into resistive plug caps the same as resistive HT leads into non or less resistive plug caps? Could this cause interference issues? Original HT leads are non-resistive, perhaps replacing like for like (resistance wise) I have the same issue as before despite new leads.....?

Thoughts?

 

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9 hours ago, Chris T said:

We got around the problem and I drove it home.  

Can you be more specific?   What problem exactly and what was the workaround you did?
 

Resistor plugs suppress RF noise which can upset radios, but also other electronics in the car which could include the ignition unit itself.  I don’t know how well the Canems unit is protected with regard to noise immunity.  

The downside is that a bigger resistance in the secondary path (eg from rotor centre to plug electrode) will lower the voltage across the plug, hence a weaker spark, but typically only 10% weaker.

An SC typically has 5k in the rotor and 3k in the plug socket plus the lead resistance itself.  So all in about 9k.  A 3.2 has a 1k rotor but not sure about the leads.  If you have a resistor plug you are adding to that also.   Most twin plug distributors do not have resistors in the rotor - what one do you have?

I use standard leads in my SC (so 9k) and non resistor plugs.      

If you think you are getting ‘noise’ in the Canems unit, I would look at the wire routing (particularly 12v feed).   Keep well away from HT.  Are there any tell tales in the Canems that indicate a reset for example?

Tbh, the most common problem I see with twin plug installs is to do with the distributor signal being out of phase with the rotor position.  Eg. the sensor wiring polarity is incorrect.   The symptoms of this are a miss under load, intermittent loss of one bank and timing that retards on RPM increase.   Trouble is, I have seen ignition maps changed to compensate which masks the actual problem. 

 

 

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Jonny, thank you. You may be on to something here..... Distributor is a 964 unit with 964 rotor and cap, non resistive HT leads and 3k plug caps. Not sure what resistance that gives me. What really struck a chord though was "timing that retards on RPM increase" something that I have witnessed. Please explain what you mean by distributor signal being out of phase, my distributor is 'dumb' no wires attached, just used to 'distribute' 2 x sparks to upper and lower cylinders from outputs of 2 x standard 3.2 coils. 

Thanks, Chris.

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Ok so in your case the distributor is not providing the ‘coil fire’ signal but the Canems still has to provide a signal to the ignition amplifiers (the two modules on the coil pack).   The polarity of this signal is important.    If it is wrong then the coils fire on the wrong edge, the timing will be out and the rotor will be in between the posts at the point of firing.  

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Hi Jonny, sorry I should have been clearer. No ignition ignitors (they are 964 items) I have 2 standard 3.2 coils each fired by Canems ECU by providing an earth path for each at the appropriate time. They both share an ignition switched 12v +ve feed and this just replicates the way a 3.2's ECU fires the coil, just with another ECU output (Canems ML1-X 35 pin plug 'n play ECU has up to 3 onboard). Top set of sparks work, bottom set of sparks work and the car has run perfectly fine like this on return from rolling road until I fixed air leaks and changed HT leads.

At the rolling road the only 'modification' was to add a resistor wire to the TDC reference sensor to pad down signal and with it noise. It seemed to work at the time but now makes zero difference.

But we are straying away from the question into a bigger can of worms..... Chris.

 

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I don't know if this is helpful or not but I have resistor spark plugs with shielded leads and normal ends. I also have a suppressor/capacitor in the wiring at the coil pack.

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I have the same Phil, except I don't have a suppressor on coil pack as I have old-fashioned coils not a coil pack.

 

 

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I wonder if something similar on the coils could help, like an old fashioned condenser?

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Maybe.... That's the purpose of the question I started with really.

What I WILL do is check 100% I have resistor plugs, but I'm sure I do. 

Cheers all.

 

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