The little capacitor to ground thing on the battery power wire to the coils. Can someone explain why this would be needed? 1994-2000 Miatas never came with one, Mazda only put them on NA6 and NB2 cars from the factory. I haven't noticed it making any difference to anything. Any car I tried it on you can unplug them plug them back in and observe no difference. Supposedly it effects the radio don't know what else.

currently rewiring a B2200 with a Kia FE3 motor using a 2000 Miata harness as a base. Wondering if there is any reason I should add a capacitor. The coils Im using are from the Kia but they look and fit like NB2 coils.

Bob

 

It helps prevent a voltage spike in the system after the coil fires. not a "required" item. but neither is a bleed hole in a thermostat. or a passenger side view mirror.

but its a good idea to have to prevent damage to the ignition system.

 

What would that voltage spike damage, hinder the performance of, or cause weird behavior in? I haven't herd of any issues specific to 1994-2000 cars that didn't come with one.

 

im very old.
and I have old knowlege.. but dont 94-00 engines have the ignitor in the coil?

when the voltage to the coil signal is sent ( grounded). there is a voltage spike in the primary side as the field collapses.
has a tendancy to fry the electronic ignition modules up stream of the coil.
the part that removes ground from the coils primary side that causes the field to drop.

not sure how they moved away from them now. maybee there is a condensor in the ECU that fires the coils ?

if you yanked the condensor from old volvo B230 and b18 b20 cars.. you ran the chance of nuking the computer that fired the coil.
might be worth youtubing a bit about it.

 

90-93 cars had a separate igniter., for all the rest igniters are internal to the coil. I'm a mechanical engineer I am dumb when it comes to electrical but I try to understand. Most of the info on the necessity of spike protection I have found on internet has to do with points type igniters and mechanical distributers not fully electronic.

 

I'd completely forgotten that certain year Miatas used external condensers.

I also can't believe that we still use the word condenser here in the 21st century. The whole rest of the electrical engineering universe has been calling them capacitors since before colored folks were allowed to use the nice drinking fountain.

Putting a capacitor in between the power supply and ground is common in a whole host of applications (automotive and otherwise) in which a large electrical current is abruptly switched on and off. It smooths out ripple in the power supply line. Removing it is not likely to cause any physical damage in the context of an automotive electrical system, but having it there cuts way down on emitted noise, which can interfere with radio reception (AM in particular), and can also induce noise into sensor readings.

 

noise into sensor readings. interesting because the same power wire that powers the coils on a 99-2000 also power's 3 O2 sensors which seem like they would be sensitive to electrical fluctuation. personally Ive had noise issues on a flex fuel sensor before but it may have been some other physics as using a grounded shield wire fixed that issue.

Another interesting thing is I'm using Kia Sportage FE3 coils. on the Kia the ignition coil control wires to the ECU are also in grounded shield wires. Miatas are not shielded. I used the shelded wires from the Kia

Also isn't the battery itself sort of like a giant capacitor in the circuit?

 

VOLTAGE >>>>>Battery ----> 10 feet of wire ----> ECU ----> 8 feet of wire ----> Ignitor -----> 5 feet of wire---> Coil ----> Plug.


sure there battery is there. but doesnt work as fast as a little condenser 3 inches from the coil.

 

What masterjr33 said.

It is, but wires have resistance, so as current flows across them, you experience voltage drop. When the current is pulsating (ignition coils draw a surprising amount of power), then the voltage drop is also pulsating. That's the definition of noise. Placing a capacitor very near the load decreases this effect.

Same reason that the folks running big, thumpin' amplifiers in their cars put big capacitors across the power and ground lines as close as possible to the amp.

 

I was wondering as well if its needed
i took the harness apart and the wires don't have anything to do with the coil wiring they go to the main plug off the ecu. It just seats there near the coils. Saying that if it actually does anything how doni wire it in. I have done a custom plug from my 1.6 harness to the coils coz the plugs where 100% the same but that i left out