Interesting: never delved into the mysteries of EDIS, before.
Best description I’ve found, so far.
https://m.autoserviceprofessional.com/article/95125/Ford-distributorless-ignition-system
Yes…you are right. It is essentially a series circuit where the resistances simply add…so the spark plug gap plus the wire resistance plus the coil resistance plus the second spark plug gap. The system has to be designed with enough voltage and energy to deal with both gaps and the wiring resistance in the coil and leads. I think the lower pressure ionised gases of the exhaust gap lowers the spark energy required…but I suspect that the system is designed with decent margin to make sure it deals with quite worn plugs…
Thanks for the info Dick, will do!
Extremely interesting Wigs, thanks for posting!
Ok so what is the correct plug gap? On the Iridium BPR5EIX-11 plug the “11” means a plug gap of 1.1mm, around 40 thou, seems like a pretty large gap. What gaps have been found to be effective with these type plugs?
Plug sequence at the coil pack checked and found to be correct, thanks for the prompt Ralph.
Les
You can safely assume the plug manufacturers are talking to the car makers to get the gap right. On one of my work cars the plugs were not changed because of a mix up in the servicing. It started to miss a few months ago. I pulled one plug to check …the gap was about 1.7mm!!! It was still running but had developed a slight miss!!! So one data point…1.7mm is a bit too much!!!
Regards
Matt
If the car was std I’d agree but it now has EDIS and possibly running Iridium plugs…so, what gap is correct? As mentioned the plug manufacturer of the Iridium plugs tells us that 1.1mm is the gap for that plug. Do I assume that’s about right for all cars using them?
I have a fundamental question about initial setup and timing of the EDIS system on our cars.
The information stated to bring the engine to TDC and set the trigger wheel accordingly. Apparently it didn’t matter which stroke or which cylinder the engine was at when this was done. But doesn’t the system require a baseline setting so that it know where to spark and if so, without it’s baseline being compression on #1, where/how does it get its “baseline”?.
I understand it’s from the missing tooth on the reluctor wheel.
Les
My XJS is running two Ford Falcon AU2 coil packs. I set the standard spark plugs at 0.025" which is the standard gap. The coil packs will have an easy life because they will not achieve the discharge voltage they were designed for and the car runs as well as it did when it left the factory. I would also feel comfortable running whatever gap the Ford Falcon AU2 runs because the coil packs were designed for this arrangement and the original spark plugs will likely handle the higher voltage. They will let you know if they can’t !!! I would set the spark plug gap either to the gap recommended for the coil pack you are using …or the original gap.
Matt
Yes but you can put that on at any cylinder TDC, no requirement on whether the cylinder is at compression or not. I know it’s supposedly ok due to the double spark operation but it’s been kinda suggested that the secondary spark might not be as strong as the first and I’m wondering if this is any kind of issue because ignition might not be using the strongest spark…I’m probably concerned over something I don’t need to be but I’d like the input of those that understand these systems better than I.
[quote=“Les_Halls, post:31, topic:376392”]Apparently it didn’t matter which stroke or which cylinder the engine was at when this was done. But doesn’t the system require a baseline setting so that it know where to spark and if so, without it’s baseline being compression on #1, where/how does it get its “baseline”?.
[/quote]
Hi Les,
With a “wasted spark” ignition system, the system ONLY needs to know where TDC on cyl #1 is. So it can’t be any stroke any cyl. This is why the crank MUST be at TDC when the trigger wheel is mounted. This can be EITHER compression or exhaust stroke on #1 - it does not matter, because all cylinders get a spark on BOTH compression and exhaust.
As long as the crank is on TDC (which WILL be for #1), the VR sensor can be mounted ANYWHERE physically convenient, as long as the appropriate teeth count from the missing tooth to the sensor (in direction of rotation) is met for EDIS-4 or EDIS-6 or EDIS-8 respectively.
A 4-cyl needs spark every 180º crank degrees (taking no timing advance into account).
Thus two coil outputs will fire alternately every 180º crank degrees.
A 6-cyl needs spark every 120º crank degrees (taking no timing advance into account).
Thus three coil outputs will fire sequentially every 120º crank degrees.
An 8-cyl needs spark every 90º crank degrees (taking no timing advance into account).
Thus four coil outputs will fire sequentially every 90º crank degrees.
So, now we have “timing” for cyl #1 sorted. So how does EDIS know where the other cylinders are?
Well, it CALCULATES it, by detecting where the missing tooth was, thus knowing now where TDC was, keeping count of the number of teeth having passed the VR sensor (and thus crank angle) and measuring the time between teeth (even taking acceleration and deceleration into account) and fires its appropriate coil outputs in the sequence it has been manufactured with, taking into account the TIME (hence crank angle) it has to wait from the last tooth to pass before the spark is due in order to fire the spark at the requested crank ANGLE (there are 10 crank degrees between teeth!!!)
Simply connecting the correct pairs of cylinders to the correct coil output ensures that they too get spark at the correct point (although they might be at either compression stroke or exhaust stroke). Still clear as mud?
Just one more comment on the spark “strength” of the compression stroke spark vs the exhaust stroke spark. Bear in mind that the spark is physically electrons flowing in a closed circuit (ie electrical current measured in Amps) from one plug terminal to the other. THE SAME current (EXACTLY the same current) WILL flow through BOTH spark gaps. The spark strength is therefore EXACTLY the same on both plugs. Due to the chemical difference in the fueled compressed air in the compressed cyl vs the burnt gas in the exhausting cyl, the resulting ionized plasma may differ but that is rather academic.
Some people suggest using .040" or .060" plug gaps as Ford do on their EDIS equipped Escorts to help produce a better burn. I settled on .030" after trying various gaps from .025" up to .040" as there was no perceivable difference. I also use standard plugs rather than iridium - tried both and no difference.
According to NGK for powerful engines you need smaller gaps:
"Since the gap size has a direct affect on the spark plug’s tip temperature and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.
A spark plug’s voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark. With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think."
David
Thank you David and thank you Philip…I’ll go check my timing…and David, I used to run MSD on the car before switching to the EDIS and I found exactly what you mention, the car ran its best on a smaller 0.025 gap
David,
I’m still working this problem and in the course of asking/searching I came across this form the Autosportlabs site. It gives a deeper understanding of the how-to’s for the system, simple enough even for me to understand! Thought I’d share with you to see if you want to post it onto the UK site…
https://wiki.autosportlabs.com/MJLJ_V4_Operation_Guide#Editing_Ignition_Map