The V8 Owners Forum -

If the coil is disconnected from the MS (or probably even connected for that matter) then you should see 12v - as the vb921 hasn't completed the circuit to ground yet.

Errrr so in simpleton terms is what i posted earlier correct?

I depends where your measuring it.
I would expect to see 12v on the harness side of the connector for each coil channel going to the MS unit with the ignition on - assuming your coils still receive 12v feed with the MS unit (and hence the mail relay OFF) disconnected.
[hmm, not sure that makes sense]

I helped someone out the other day with a 4 banger, using wasted spark. the two spark channels from the megasquirt to the coils were via spade connectors - so we could just pull them apart and check that we had 12v on each one. Turns out he wired the coil packs up wrong.

Just to clarify with the ignition on which means the centre pin is live and reading 12v the outer two pins aren't reading anything.

Like so.



You dig?

That's wrong. But you measured the coil and it was good. With the MS connector unplugged and power to the centre pin you should have 12V on the outer pins.

Ah, so what does this mean?

Ps, i've sent you some pics of the ecu.

It means you coil in knackered.

Have you tried measuring the resistance between center pin and the 2 outside pins.

r2d2hp wrote:It means you coil in knackered.

Have you tried measuring the resistance between center pin and the 2 outside pins.

Indeed. remember the coil is just a bit of wire, so 12v at one end will result in 12v at the other end.

So the 12v feed gets split between the two coils and returns to the MS. You should see 12v at the gnd end when just supplying 12v to the feed.

12v-------------CCCCC--------gnd (or to ms)
:__CCCCC-------gnd (or to MS)

No no no this is the wiring plug i'm measuring unplugged not the coil itself.

With the plug unplugged and ign on 12v is in the middle pin and 0v on the outer pin. Thats should be correct i believe.

I've checked resistance of the coil and thats fine. I have two coils from different cars so i'd be surprised if i picked two that don't work.

I havent had the lot fitted and pluged in and checking to see if i have 12v on the outer pins yet, i should check that also i guess!

That makes more sense. Next to do is unplug the coil connector off MS, frig 12V to the coil and measure that you get 12V at all 4 points on the MS connector. If you have then you definately need to get the MS to me for a check.

I'll do that tonight!

Would it be ok to ground one of the coils outputs with a switch inline and see if i can get them to spark?

ihatesissycars wrote:Would it be ok to ground one of the coils outputs with a switch inline and see if i can get them to spark?

Don't see why not, I've done it myself with a normal coil in the past to check it out.

Have you wired in a 25uF capacitor on the input to the coils? This will stop it working if it's wired in series instead of parallel.

Next thing is to double treble and quadruple check the earths. IMO you can't have enough of a good earth

Just in case you're getting a bit fed up; keep going, it's a steep learning curve and a bit of a bastard to get going but once it's running right you'll never go back to a normal setup. It's main problem is that there is so much to configure, which is also it's main asset as you can do almost anything with it.

Kev

Well I have 12v on the coil output/trigger wires so i'm guessing its ecu fault finding time?

Don't worry kev! I don't quit! It WILL work and work well!

ihatesissycars wrote:Would it be ok to ground one of the coils outputs with a switch inline and see if i can get them to spark?

i tried this the other day and it didn't work. I assume i needed a capacitor[condensor] accross the switch to stop it arcing (just like points)