25 microfared cap on coil pack
Moderators: JeffC, rdoherty, stieg, brentp
25 microfared cap on coil pack
Is this needed the wiring diagram does not show it
Hi John - welcome!
In simple terms, no.
If you already have it on/close to your coilpack, then leave it on - but don't go hunting for one if you haven't got one.
Perceived wisdom is that it's there for radio interference, and many Ford installations never had it at all.
Brent - maybe worth putting this in the Wiki - it comes up fairly regularly
Regards
Martin
In simple terms, no.
If you already have it on/close to your coilpack, then leave it on - but don't go hunting for one if you haven't got one.
Perceived wisdom is that it's there for radio interference, and many Ford installations never had it at all.
Brent - maybe worth putting this in the Wiki - it comes up fairly regularly
Regards
Martin
Actually. it's not there for suppression purposes.
It provides a voltage reserve function in some chassis variants where for various reasons the wiring exhibits a significant voltage drop on each spark event.
Put a scope on the +V feed to the EDIS pack on a '97 V8 LTD and you'll see what they were 'fixing'.
To an OEM like Ford a small component such as a capacitor is cheaper than a decent wiring harness.
I have a genuine Ford harness that uses 16AWG wire for everything!
btw, those of you who are electronics whiz kids can calculate the reactive frequency of a 25uF capacitor. It's a REALLY low frequency and immediately tells us that either there was a problem with some really weird low frequency interference or it wasn't to do with interference in the first place.
We (ie the usual MegaJolt user) don't have the problem of voltage drops - we just use thicker wires!!
It provides a voltage reserve function in some chassis variants where for various reasons the wiring exhibits a significant voltage drop on each spark event.
Put a scope on the +V feed to the EDIS pack on a '97 V8 LTD and you'll see what they were 'fixing'.
To an OEM like Ford a small component such as a capacitor is cheaper than a decent wiring harness.
I have a genuine Ford harness that uses 16AWG wire for everything!
btw, those of you who are electronics whiz kids can calculate the reactive frequency of a 25uF capacitor. It's a REALLY low frequency and immediately tells us that either there was a problem with some really weird low frequency interference or it wasn't to do with interference in the first place.
We (ie the usual MegaJolt user) don't have the problem of voltage drops - we just use thicker wires!!
So much for conventional wisdom! Thanks aarc240.
Seems that most people simply translate the original use of condensers with the mechanical points system to the electronic world. As an example: http://www.jetav8r.com/Vision/Ignition/CDI.html
Seems that most people simply translate the original use of condensers with the mechanical points system to the electronic world. As an example: http://www.jetav8r.com/Vision/Ignition/CDI.html
I never thought the old-fashioned condenser and the EDIS capacitor were for the same purpose (they're on the different coil connections, after all), but I freely admit I didn't think the capacitor was there for 'voltage reserve'...25uF at 12v sounds very small to me to have any appreciable affect, but I don't have the skills (any more!) to do the sums to work it out.
Looks like the Wiki needs a bit of massaging!
Martin
Looks like the Wiki needs a bit of massaging!
Martin
Martin,MartinM wrote:25uF at 12v sounds very small to me to have any appreciable affect
You're 100% right there, it's actually about the smallest value that will make sufficient difference to 'fix' the problems!
It doesn't fully smooth out the voltage glitches on the LTD but it does _just_ prevent misfires.
Just out of curiosity I substituted a 10uF cap and the car ran fine most of the time but misfired under hard acceleration.
Ford must have spent some time isolating the problem (or more likely they tested on lots of customers).
You and I would figure that a 100uF rated at 63V would be good even if it cost 10c more but OEM's don't (usually) work that way.
It's worth keeping in mind - a strange or random miss under hard acceleration at high speed would warrant trying a similar or slightly larger capacitor on the EDIS supply rail.
Just not TOO large - after all, the supply then has to charge it up at switch on and there's nothing to limit inrush current.
For those wondering why too large a capacitor would be significant I'll give a real-world example from a remote area power supply (RAPS).
It has a 96V DC (battery bank) power supply and originally a capacitor bank totaling 56000uF. Sounded good on paper (sales type literature) but there were several failures where either battery life was shorter than predicted and/or reasonable or the battery terminal(s) failed inexplicably.
While investigating I put a voltmeter on the +Ve feed cable to see what voltage drop we had along it.
No problem there but by chance I left the meter in place while cycling the system.
A sudden and violent swing on the meter pointer made me sit up and take notice!!
To test thoroughly I took the system down and discharged the capacitor bank completely (via a large resistor).
On power up that voltmeter momentarily damn near hit the top of the scale at 100V, even after adding some damping to it on a subsequent try.
Calculating the resistance of the cable using the usual voltage drop along it at normal load current and then using that figure together with the momentary voltage differential along the cable showed that for a very brief period those batteries were having to supply about 13000 amps!
A new capacitor pack totaling 2200uF solved the problem without introducing any new ones so I left it at that.
OK, I don't think anyone will get THAT carried away with smoothing capacitors but you can understand why more is not necessarily better.
Art C