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Richie-Van-GTi

Dwell times

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Richie-Van-GTi

Hi, my current set up uses a VAG wasted spark coil with built in igniters. Problem with this is i cannot get my tacho working in the car. The ecu output wont drive it even through pull up resistors or relays etc.

Im wanting to swap it back to a dual channel ignition amp and a typical PSA wasted spark coil then i can drive it through the usual resistor/diode mod. Also keeps the car pug parts under the bonnet.

Anyway, my question is what to do about dwell as im sure it will change... increase? With this set up?

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petert

I assume you were <2ms with COP's? You'll need at least 3ms with the regular dual channel ignitor. You'll need to confirm with an oscilloscope in order to maximise the dwell.

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Richie-Van-GTi

Its not COPs currently, its wasted spark but has built in igniters in the coil as the ecu cant drive the peugeot wasted spark coil. I think thats at 2.5 dwell, will have to double check. If i am right in thinking it will be slightly higher it gives me a starting point.

Never had to scope for dwell, are there any clear symptoms of incorrect dwell and how to know which way yo adjust?

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petert

Coil will get excessively hot if too much dwell. I’d leave it at 2.5ms to begin with. That’s quite low. Search on Youtube.

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Thijs_Rallye
On 6/27/2022 at 6:57 PM, Richie-Van-GTi said:

The ecu output wont drive it even through pull up resistors or relays etc.

What kind of signal does the ECU provide? I've got it to work with a modified relay and the ECU's PWM signal, using the relays coil as a faux ignition coil.

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petert
1 hour ago, Thijs_Rallye said:

 I've got it to work with a modified relay and the ECU's PWM signal, using the relays coil as a faux ignition coil.

Nice. Did you read this?

 

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Thijs_Rallye
18 hours ago, petert said:

Nice. Did you read this?

Not until I saw your post :). I've made this relay after the RFS Nodiz conversion in 2014, found the original idea on some obscure Lotus forum if I remember correctly. (who had a 5V PWM to work with, so resistance values and transistor type are different)

 

It wasn't the most aesthetically pleasing construction but it works and all is confined in the original relay housing :)

 

 

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Edited by Thijs_Rallye
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Richie-Van-GTi
On 7/5/2022 at 11:27 AM, Thijs_Rallye said:

What kind of signal does the ECU provide? I've got it to work with a modified relay and the ECU's PWM signal, using the relays coil as a faux ignition coil.

It provides a 50% pulse which requires a pull up resistor. Ive tried resistors of varying ohm and also tried using modified coils to create a collapsing coil effect, aka faux coil. Nothing works.

I have all the stuff to swap to a seperate ign amp and wasted spark coil anyway along with the relevant diodes etc to make a tacho drive that i know works with the coil.

Just not had time to do it.

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Thijs_Rallye
9 hours ago, Richie-Van-GTi said:

It provides a 50% pulse which requires a pull up resistor.

5V or 12V? You could give this relay fix a try, only thing to take into consideration is what voltage the PWM signal is. For 12V the schematic / resistance values are ok, for 5V it needs some tweaking.

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