Hi there, after some help in a slightly different scenario than normal!
I’m using a 2002 VVT engine in a kit car which is hooked up to an Emerald K6 aftermarket ECU and new wiring loom. The kit manufacturer makes a plug & play wiring loom for the earlier engine variants using a single coil pack, they have adapted this for the twin set up on the VVT variant by running the coils in parallel, i.e. they are both fired at the same time rather than alternately as needed. I replaced the packs back in September when the car went for its IVA road worthiness testing and was tuned on a rolling road. The car achieved a comfortable 171 bhp without being pushed to the limits so very pleased with the output - it’s totally standard other than running on ITB’s and performance exhaust! When I got the car back it ran beautifully and sounded amazing! One day however it wouldn’t start, and it hasn’t started since! It cranks fine, the ECU is reading all signals correctly, there is fuel getting to the injectors so my thoughts were the coil packs have failed. I tried an inline spark tester and was getting a low orange flicker indicating there was some output from the coil pack rather than nothing at all. I’m loathed to splash out for another pair of coil packs, but its the most likely source I believe of the non-start problem. Now I appreciate coil packs can fail, but both of them at the same time, twice now?! My thoughts have turned to wonder about the wiring feed to the packs which as I mentioned is firing both packs continuously, I wonder if somehow this is causing issues with the packs burning out? These things are meant to last for billions of fires so i’m not convinced, but can’t think of anything else causing the failure. Advice greatly appreciated!
Hi Nick
I am surprised that there is any difference with the function of your VVT coil units compared to the earlier non VVT car. There is no real difference as each unit fires two cylinders - 2,3 and 1,4. Earlier cradled coil units have exactly the same principle as the later units that are mounted individually on the cam cover. As far as I am aware the units are charged up permanently through the low tension circuit whilst the ignition is on and discharge in cylinder firing order when the car runs.
These VVT coil units do fail but bad luck for both to fail completely at the same time.
Does the aftermarket ECU facilitate onboard diagnostics or even the old style Mazda diagnostic socket? I would recommend a check for error codes before doing anything else, although as you may know the coil units do not directly produce an error code.
There is a reasonable chance that something else other than coil units is the problem.
Thanks for the reply.
I was under the impression that the earlier variants used a single coil pack at the rear of the engine with HT leads to all 4 spark plugs with the coil would firing to each plug in firing order, a bit like an old fashioned distributer would. The difference being the twin head mounted packs on the VVT variant are fired by the ECU alternately depending on which cylinder is firing. As you say, each pack fires 2 plugs which is done simultaneously, a wasted spark set up. If my understanding is incorrect here i’m happy to be corrected!
I understand the principle that the kit manufacturer has used in their wiring loom should be ok, but as i’m the first to try this i’m being the guinea pig here!
The Emerald K6 doesn’t doesn’t run a fault tracking facility, I can only see live data so I can see it is reading all sensors and sending signal to fire the injectors and the coil packs. There is nothing left of the original Mazda loom or ECU so cant fall back on reading fault codes that way.
I know the engine can run perfectly fine, it lasted for 4 months including a rolling road session, hence leading me to think there might be a cause for the coil failures rather than it just being bad luck! It’ll get expensive replacing them all the time!!
As I understand it the coil unit principle is the same for all the cars(MK1 - MK2.5) except perhaps the MK1 1.6 which has a slightly different arrangement. Firing is controlled by the Cam angle sensor via the ECU and the igniter contained within each coil unit. The MK1 1.6 has a separate igniter unit.
If the car ran fine for 4 months without any coil issue and this ECU has worked with MX5 engines with the older style cradled coil pack engines, I would not assume coilpack failure.
There are so many of these VVT 1.8 engined cars around. Given the lack of assisting diagnostics, i would try your interchangeable coil units in a working car to confirm whether or not this is the issue. Next I would try the CAS, crank and airflow meter if fitted. Most of these are easy/quick to test.
I have sent you a PM re the coilpacks, should they be required.
Is anyone local to Andover in Hampshire who would mind me trying out my coil packs on their car to check they’re operating ok? I don’t mind coming to you!
Anybody with a 1.8 VVT near andover who can help Nick out