MkIndy7
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| posted on 4/8/07 at 10:57 AM |
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Megasquirt recieveing a back feed
After setting up the Megasquirt to run the timeing only I'm coming upon an unsual problem.
Before the car has been started the ignition and Megasquirt turn off fine.... however when the engine has been started it won't turn off 
You can stop it by pulling out the Immobiliser, or removing a 10A fuse that I thought was only for Headlights and indicators.
Whats the best/easiers soloution for this? is there a diode thats 10A that I could put inline with this fuse to prevent the back feed? or is there
another way.
As ever, any help would be grately appreciated 
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paulf
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| posted on 4/8/07 at 11:20 AM |
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Where is the centre terminal of the coil fed from?this should be an ignition switched live with about a 10amp fuse , the megasquirt ecu should also
have a seperate live feed fused 2amps that is ignition switched , the ignition shouldnt operate without both of them being switched to live.
Paul
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MkIndy7
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| posted on 4/8/07 at 11:39 AM |
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The coil and Megasquirt are both fed from seperate fuses i've installed in a new fuse box. As to give the Immobiliser an easier life i've
fed the new fuse box via a relay, I'm presuming it must be this relay thats holding in after the ignitions being switched off.
As the Immobiliser and its wireings a bit of a black art.. and wires! and possibly where its back feeding from via that 10a fuse some how, I was
wodering if there was a bit of a quicker fix.
"the ignition shouldnt operate without both of them being switched to live"
The ignition does operate in this way when you turn the key etc... its just once the engine has been started it won't turn off!.
I'm still thinking of a feed that would only be present when the engine has run and then stopped... or would be common to the headlight and
indicator fuse, (this circuit is permaneantly live for the sidelights and hazards to work)
On some relays I liberated from the Scrapyard before they appeared to have diodes or relays in them because the coil would only operate with the
correct polarity, I'm wonvering if these are used on ECU's and low power applications to make sure there is a proper feed to activate the
coil and not just a back feed strong enough.
Could do with it MOT ing this afternoon if I can find somewhere and not sure they'll be happy with pulling the immobiliser out to kill the
engine.. although old Land Rovers you had to pull or push a knob on the dash!
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paulf
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| posted on 4/8/07 at 11:52 AM |
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I remember something about westfields having a problem with the electric fan backfeeding to the ignition and making it impossible to turn off once
running.
Can you feed the relay from the old ignition supply assuming it was ok before hand ? or if it is a backfeed then try to connect it into a seperate
circuit that does just the ignition, the lighting circuit surely isnt connected via the immobiliser though?
Paul.
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MkIndy7
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| posted on 4/8/07 at 11:59 AM |
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Thats what I thought, the lighting should have nothing to do with the immobiliser.
I really ought to know my own wireing better, but it was done about 4 years ago and believe me i've learnt alot since then! at the time it was
"functional" lol.
I'm wracking my brains what can be related to it working ok before the engines started and not after.. what is holding the feed on.
I've just been out to pop it back into the garage and it stopped properly as it should. I thought when i'd connected more of the electrics
up this morning i'd cured it then, but it must just be when its cold that it behaves.
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omega 24 v6
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| posted on 4/8/07 at 01:20 PM |
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Could it be getting a feedback through the alternator field circuit??? Just a thought but if you've pickrd up the ign feed from this circuit
AFTER the bulb (warninglight) the the alternator will keep it running. A diode could be a quick fix although you've not really solved the
problem. Worst that could happen is blowing the diode as long as everything else is fused. Try pulling out the fuses one by one till it stops and then
check through that circuit.
If it looks wrong it probably is wrong.
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MkIndy7
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| posted on 4/8/07 at 03:11 PM |
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quote:
Originally posted by omega 24 v6
Could it be getting a feedback through the alternator field circuit??? Just a thought but if you've pickrd up the ign feed from this circuit
AFTER the bulb (warninglight) the the alternator will keep it running. A diode could be a quick fix although you've not really solved the
problem. Worst that could happen is blowing the diode as long as everything else is fused. Try pulling out the fuses one by one till it stops and then
check through that circuit.
Hmm you could have a point with the alternator powering it somehow. We have got a starter switch that takes a feed off either the alternator or the
oil pressure light (as they go out when the engines running to stop people pressing it accidently).
Having a bit of a dim moment... where should the diode go in really, the circuit with the 10A fuse in, the wire to the ignition realy (from the
immobiliser) or in the feed to the megasquirt and coil.
Also which way does the silver band go on them?, can never remember!
[Edited on 4/8/07 by MkIndy7]
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omega 24 v6
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| posted on 4/8/07 at 06:17 PM |
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Youd really need to fit the diode at the point of feedback as the current is still going to flow through the diode in the correct direction anyway. If
your sure it's at the 10 amp fuse you could fit it at the live side (power into) the fuse with the silver bar pointing towards the fuse. This
would stop any feedback at this point.
If it looks wrong it probably is wrong.
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MkIndy7
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| posted on 4/9/07 at 10:11 PM |
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Thanks alot Folks
We've put a Diode in line with the Dasboard light, so it still illuminates when the Ignition first goes on.. and thus presumably works still
when its required.
No idea as yet as to how its was backfeeding but I suspect it was through the Immobiliser we wired in.
As we wasn't sure of the Amperage rateing of the Immobilizer we fed all the Injection system through a relay thats coil was fed by the
immobliliser.
A back feed from the alternator charge light must have been just enough to keep this energised, even after turning the ignition completely off.. it
would just keep running until you pulled out the immobiliser, or flashed lol.
Hopefully thats Cured it... certianly has so far in the limited testing I've done.
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matt_claydon
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| posted on 4/9/07 at 10:20 PM |
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I have the same problem with the engine continuing to run after you switch off, except the engine stops when you pull on the handbrake! Bizarre 
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omega 24 v6
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| posted on 4/9/07 at 10:23 PM |
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Well done always good to hear when and how a problems been solved.
If it looks wrong it probably is wrong.
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andrenel
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| posted on 6/11/07 at 10:05 PM |
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cheers I have exactly the same feture except mine only accurs when I have more than half a tank of fuell, Have to pull up handbrake to switch
off.
In my case I know it is backfeed from the altinator, will fit a diode when it gets to annoying.
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