My Hopes
After much reading about the Coil on Plugs and Dwell reducer circuits on mx5 forums, and much umming and ahhing, I had a Clarkson moment, said "how hard could it be?.." pulled my finger out and decided to build one..
I'd read a bit on people saying they'd have smoother idling, and improved fuel economy, tho nothing was wrong with my engine idling, i'm always up for FE improvements.
Getting the Parts
After some checking on ebay for the COP drivers, i'd settled on PureMX5's kit for $118 delivered, including prewired connectors.
http://puremx5.com/?page_id=98
and has them available from eBay:
http://www.ebay.com.au/itm/Mx5-Coil-Plu ... 193wt_1398
(Significantly cheaper then landing the COPS from the US, and then forking out for the connectors..)
Holding the COP in your hand with the connector facing you, from left to right the pins are:
1) Earth
2) Trigger
3) Tach
4) Positive
I got a little freaked about the wiring on the connectors, the ordered part's wire colouring didn't correspond to the COPs part number (90919-02239) pinout wiring:
To me, and the rest of the world, the colour red suggests positive, but by using the known pinout wiring, i re-labelled them during my installation. Red in these wires is negative!
I'd hooked them up to a high current powersupply and tested them with the normal pinout wiring and generated a nice zappy spark.
Confusion aside, they are pre-wired and have saved an amount of fiddly time having to do it myself.
My Concerns
Another thing I was very curious about but couldnt find a comparative pic was with the length of the COP versus the standard ignition plug.
How high would it stick out?
Would i need to remove the rubber grommet from the base of the COP to make it fit?
Do i need to trim the edges of the COPs base to make it fit snugly in the rocker cover top?
How do I make and mount a securing latch over the COP drivers on the rocker cover and how would they fit physically.
one photo, and it says it all.
The part of the COP which sits in the engine head is near-as-makes-no-difference the same length as the OEM lead.
The width of the COP appears to be a tight fit in between the cam humps in the rocker cover, but it *does* fit.
The part of the COP which touches the spark plug is actually a spring, so although it will sit on the plug, and the rubber head or rubber bottom (whichever way you look at it) that wraps around the plug doesn't feel as tight gripping around the plug as i'd hoped but does seat against it.
All good.
More on the securing the COPs bit later.
Building It
The COP drivers arrived at lunch on Monday, after work, i went to Jaycar to get some supplies.
I bought several 2 meter lengths of wire. It was handy they had pretty much the colours i wanted:
Thick black for earth, thick blue for the supply rail voltage, thinner yellow for the tach line, brown and brown with a white stripe for the trigger lines. (pretty colours)
A length of a heat shrink tube, and thicker length to bundle the 5 leads together.
Two thickness of the ribbed lead protectors to house the leads to protect them from rubbing and being damaged once the loom was completed.
Using my original(spare) rocker cover as a template in my den, saving me from the cold winter outside, I placed the first COP in to find out the way i'd like it oriented. Theres plenty of choice as the plugin for the connector is angled nicely it can exit the cop over the inlet, or toward the front or rear of the engine. The screw in lug on the COP head restricts only a few choices. I opted to exit the loom over the exhaust cam.
I soldered up the first COPs loom and heatshrunk it close to the connector so the original connectors incorrect colours weren't visible.
Next i exposed the wire at regular intervals to allow the next connector to be joined in.
Plug 1 and 4s trigger wire is the "brown with white stripe" you're seeing in this picture.
Each of the COPs connector wires were soldered to the main loom wiring, individually heatshrunk and then all the section was encompased in a larger heatshrink tube. This was done to promote rigidity and as an extra wear protection against rubbing.
This pic shows COPs 2 and 3. The brown signal wire on the MX5 loom triggers both of these COPs.
This pic shows the first and second COPs installed. I wanted to keep my wiring loom as tight as possible so i wouldnt need much in the way of support to hold the loom still in the engine bay.
Three COPs connected. Now the brown wire with white strip needs to be exposed again to join the trigger line for the 4th COP.
And so forth and so forth..
I also had an existing loom from a spare engine that id sacrificed for one plug to interface the existing ignitor wiring.
I temporarily connected the loom together and plugged it in, and bolted the earth to the head.
The car started first go. I turned it off, and got my phone so i could film it:
This video shows the second time i started it.
yay.. By now it was 8pm.
Nex to tackle the Dwell Reducer circuit.
I missed out on the group buy for this on the forum, so i decided to make my own.
I'd written up a parts list based on the design from the group buy circuit. This uses a different comparator circuit to another later design, but has less parts. The latter design uses transistors to drive the output signal lines (brown wire and brown with white stripe wire).
All up about 6$ of parts, and i had my own pack of regulators from a previous eBay purchase and project, saving another $2.00 which i put toward my next coffee.
I also opted to buy a bunch of capacitors, which i could have bought for $6.00 but opted to go extra redundant with it, and splurged $23 on instead.. there goes my next coffee.
...and made my own version of the circuit board layout to suit a veroboard with strips of circuit tracks.
Here is the initial bit of the circuit board.
I'd also soldered up each used track to minimise the effects of moisture over time corroding the copper.
Later this will be sealed up with silicon after a few days of working correctly.
Heres an in progress video of the dwell reducer board being built.
The reserve capacitors i chose were 25v 4700uF. They were $2.85 each.
Having 8, i was going to place 4 beside each pair of triggered COPs but later decided to keep them as far away from the hot engine but still in the engine bay. So i grouped them together.
If you choose to get these, ensure they have the pressed/denty/mercedes logo seam things on the tops of them. If the capacitors decide to fail or die, these Mercedes things will crack open slightly allowing the cap's pressure to vent 'safely' thought them on the form of copious smoke. If the lid of the capacitor is a solid can thing, if they fail for whatever reason, they *will* explode, and the results will look like the way we'd like to see justin beiber..
I've wired the caps in parallel, the earths are arbitrarily on the outside, joined together by a thick black wire. The circuit tracks are reinforced with loads of solder, ensuring a thick track protected from corrosion and able to transfer much higher current.
The positive lines i've linked in the middle. I'm using the actual capacitors leads for their wiring as well as the solder reinforced circuit tracks.
On the top left of this image, you can see the OEM Mazda socket that joins into the ignitor's loom.
This pic shows the test loom with the dwell reducer in place.
I'd plugged this into the car, and it started first go. Woot.
By now it was just shy of midnight. I didn't want to ruffle my neighbours so i called it a successful night.
Tuesday at lunchbreak, i took the loom and circuit to Jaycar to find a suitable ABS plastic box.
This one fit perfectly.
I began tidying up the loom. I'd placed the wiring in ribbed cable protectors then wound the loom up with marine grade water tight electrical tape. This made the loom comfortably rigid. Still able to flex where it needed to but able importantly, to hold itself solid on the rocker cover without loading up the connectors on the COPS.
On the wiring loom heading to/from the box, i'd carved a neat and firmly tight hole on the boxes edge. It was tight enough to rigidly support the circuitry without any movement, and i'd also secured a cable tie on the inside to prevent it from being pulled out under a more extreme condition.
Heres a close up of the waterproofing tape over the ribbed plastic shield on the input and earth connectors.
...and of the COP connectors.
Here's the completed setup.
And because i'm completely crap at fabrication of any sort, this is my TEMPORARY securing idea for the COPs to the spark plugs..
I used some spare central locking brackets bent to 'shape' to hold the COPs. Cylinders 1 and 4 are extremely secure, as they each have a bolt each. 2 and 3 share a bolt and are can jiggle a little bit. None of them can move up or down, they are firmly in place. The central locking bracket is bolted via the rocker cover bolts. In time i'll get an engineering workshop to fabricate a neat bracket for me.
The Results
i tried using my timing light. As long as i held the timing induction sensor against the cylinder one's COP head, the timing light worked. I was curious about this for a while.
At 10:40pm Tuesday night, I did my first test drive using the system.
I'm pretty intune with minor and subtle changes in my car. Psychologically I'm happier with the setup as it's replaced the ignition leads and thats one less thing to worry about breaking down over time but normally doing your own mods to a car makes it feel faster/better/stronger.. Your brain does wonderful things.. heck even washing the engine makes the car feel "quieter" and stronger to drive. However I have noticed no difference in idling smoothness or basic street drivability. Haven't noticed anything different on heavy footed acceleration to redline either compared with my normal ignitor setup.
Either case, this isnt necessarily bad, as on random occasions, especially on cold mornings, the roadster would start VERY rough with a low COLD idle (1000rpm), then after 2 minutes would pick up to 1500rpm, then warm to 850rpm. This didn't happen every morning, again, it was somewhat random. A way of making it happen every time for a week would be to wash the engine. This would be moisture/water build up on the ignitor or sparkplug wells but even after i'd blown the water out, it'd still start consistently poorly for a week or more. I figured the ignition system could do with a change just for that alone. The change i'm happy with in that regard. Hopefully i'll never again experience the rough starting.
Last weekend, under ideal temperature and weather conditions (about 5deg C, no wind) i drove 120km using a revised air intake design and modified higher flow air filter (cleaned). I topped up the fuel with BP 98octane and went for a drive on extremely flat straight 100km roads north of Bendigo, i achieved a fuel economy of 12.35km/L (8.1L/100). This was with 6000km of dirty oil 10w-40 oil, old plugs. I also drove extremely light footed, taking my time to accelerate to cruising speed as there was no traffic about at hour i drove. Considering the circumstances, on an engine rebuild 13,000km ago, i thought this was a little low. Was expecting high 12/s low 13s for mileage. Anway, its a fixed point of reference for the following.
Last week i replaced the oil with 10w-30, and replaced the plugs. (standard mx5 bkr5 whatits..)
Here's the interesting thing:
Last night after the install, I topped up with the same BP fuel, i drove this time only 60km (because of time, and it was a school night) on the same road. Same air intake/filter cleaned again. Pretty much exactly the same weather conditions, 5 deg c and importantly no wind and about the same air pressure according to my weather app on my phone, same time of the night, same driving style. Same acceleration distance, basically drove from filling up till 30km away, coasted down in gear, uTurned, slowly accelerated to 100kph, same shift points during acceleration etc.
Here i'm expecting a noticeable difference in return fuel economy..
However I had exactly the same fuel economy.. 12.35Km/L.
Tho i'm happy i wont have to worry about ignition leads again, i'm a little upset this better ignition system has made zero difference to my fuel economy..
I'll drive to Melbourne via the hilly Calder Highway on thursday evening for The Garage meet and will see how the economy/power is there.. Maybe it handles better under heavier loads up hill? Still hopeful..
I will modify the loom tonight and extract the 12v feed line for the COPs, intercepting it via a high current relay and triggered by the fuel pump relay. I didn't think far enough ahead of the supply voltage and it's fusing requirements based on the OEM ignitor loom.
It wont hurt to do the mod but i really honestly cant see a difference happening.
I fear the fuel economy 'myth' is busted.. I guess thats why i haven't seen anyone's direct results on fuel economy differences with and without this setup.
Thats my story and for me i've answered all the questions i wanted to know about the setup.
If you're curious about this mod, hopefully it will answer some of yours too.
