Capacitor type & rating for LSx ignition coils

[Healey3000]

Hi,

MS documentation shows the need (optional) for a pair of caps with the LSx ignition coils. However, cap type and voltage rating are not mentioned.

Since there can be flyback spikes from the coil primary, wouldn't a diode also be required, allowing for a lower voltage cap? Say, 100 volts?

Thanks.

[nathaninwa]

I don't have any data, but on 6 lq9 coils I installed one capacitor setup from a 1g Mitsubishi coil setup, and to date no problems after 2 years of running

[DaveEFI]

A diode will attempt to remove the flyback pulse - and it's that pulse which is needed to develop the spark. A suitable capacitor will provide a low impedance path to AC currents - ie noise.

[Healey3000]

I don't have any data, but on 6 lq9 coils I installed one capacitor setup from a 1g Mitsubishi coil setup, and to date no problems after 2 years of running

Hi,

Does it show a voltage rating? Any other information on it that would suggest what type of cap it is?

Where does GM place their capacitors in their applications? It does not appear to be in the wiring harness itself.

Thanks.

[jsmcortina]

Where does GM place their capacitors in their applications? It does not appear to be in the wiring harness itself.
Thanks.

As far as I know, they don't.

James

[Healey3000]

A diode will attempt to remove the flyback pulse - and it's that pulse which is needed to develop the spark. A suitable capacitor will provide a low impedance path to AC currents - ie noise.

Hi,

Assuming that the power lead is a low-impedance source (which it should be), the flyback pulse amplitude will not be large. What voltage cap would you suggest?

Thanks.

[Healey3000]

Where does GM place their capacitors in their applications? It does not appear to be in the wiring harness itself.
Thanks.

As far as I know, they don't.

James

Interesting. Why do we need it? Does GM do something in their ECU (that we can replicate in MS)?

[jsmcortina]

I'm not convinced that we do. I've not used them.

James

[nathaninwa]

I'll back up my cap install with an LS I did in which no cap was used and works fine as well

I added mine while tracing down a cranking sync issue, but didn't solve it at the time, but has not hurt at all

[Healey3000]

I'm not convinced that we do. I've not used them.

James

Good to know; thanks. When and how did the caps enter MS lore? I see so many websites and forums referencing the Megamanual. Therefore, it must be true

[Healey3000]

I'll back up my cap install with an LS I did in which no cap was used and works fine as well

I added mine while tracing down a cranking sync issue, but didn't solve it at the time, but has not hurt at all

Thanks. No caps for me!

[DaveEFI]

A diode will attempt to remove the flyback pulse - and it's that pulse which is needed to develop the spark. A suitable capacitor will provide a low impedance path to AC currents - ie noise.

Hi,

Assuming that the power lead is a low-impedance source (which it should be), the flyback pulse amplitude will not be large. What voltage cap would you suggest?

Thanks.

I'd say the purpose of this cap is to reduce RFI - mainly for the car radio etc. Same as you'd do with points ignition. But I doubt it's needed otherwise. But also will do no harm.
IIRC they are usually about 1-10 microF 300v.

[xrattiracer]

No caps here. I dont recall reading anything about them even when i built my harness.

[Dasman56]

I ran with out a cap and LS coils for several months but was getting alot of noise on the frequency based sensors (maf & flex sensors).
Installing a capacitor fixed the issue 100%

[Dennis930]

The capicator recommendation came from Megasquirt testing by Bowling & Grippo. See link: http://www.megamanual.com/seq/coils.htm#ls2

[Healey3000]

I ran with out a cap and LS coils for several months but was getting alot of noise on the frequency based sensors (maf & flex sensors).
Installing a capacitor fixed the issue 100%

Thanks; what kind did you use? Did you find that it had more to do with the power bypass caps or the ones on the trigger lines?

[Dasman56]

The only automotive grade cap I could get was 0.47uf and was placed on the coils power feed. I never had any signal noise on the voltage sensors only the frequency ones.