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Ignition wiring 
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Part built GTM

Joined: Thu Nov 22, 2007 10:31 am
Posts: 113
Post Re: Ignition wiring
Hi Juls,

I'll have a look at tracking it to source.

I have purchased a second hand mems 2 ECU and found a man to decode it. Hopefully that will be a successful workaround...


Sat Mar 30, 2019 5:22 pm
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Part built GTM

Joined: Thu Nov 22, 2007 10:31 am
Posts: 113
Post Re: Ignition wiring
Quick update.

I unplugged the mems immobiliser and purchased a decoded mems 2 ECU. The chap who decoded it ran diagnostics and said all was OK. I installed and I have the same issue unfortunately. No spark.

So i have power going into the relay box on wires: brown (x2), brown and slate and white. I pulled the relay box apart and tested all four again and, with 12v applied, they all function.

I have power to all of the sensors including the ECU on brown and pink. However, when I turn the key to pos 2 the engine management relay and oxygen sensor relay do not move. The starter works when turning the key, as does the fuel pump. I seem to have no power on blue and red going to the oxygen sensor and I have no power on black and green from the relay to the ECU.

Any thoughts on what to try next? My brain hurts.


Sat Apr 06, 2019 4:51 pm
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Joined: Thu Jun 27, 2013 11:32 pm
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Location: Norfolk
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Post Re: Ignition wiring
Hi i hope you dont mind just a thourght
Do you mean the black relay b5ox with the 4 relays in side it i don't no if you no this there are 2 different types.
one is for engine and fuel pump and the over i think is for aircon but they look just the same and will plug in

Air con relay,
Part no. YWB100800
Image

This is the one for the engine
Part no. YWB100970

Image

I think have that right way round :?:

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Last edited by catsam on Sat Apr 06, 2019 8:23 pm, edited 1 time in total.

Sat Apr 06, 2019 6:58 pm
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Joined: Sat Apr 08, 2017 3:08 pm
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Location: Worksop
Post Re: Ignition wiring
These may help you sort where your wired ought to go

http://www.mgfcar.de/schedules/index.htm
http://www.mgfcar.de/schedules/

I'm running a 1.8 after removing the A series (not in a GTM), I got the 5AS chipped so the rolling code is fooled, it's a few years now but I can probably get you the guys details if required.


Sat Apr 06, 2019 7:31 pm
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Joined: Thu Nov 22, 2007 10:31 am
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Post Re: Ignition wiring
Thanks - I've checked and it is the correct relay pack (that would have been embarrassing!).

So, 12v going into the coil pack, continuity of both black and white earth wires back to the ECU is good. There is no continuity from black and white to engine ground though, is that a problem or is that controlled by the ECU to generate the sparks?

There is resistance between between pins 1 and 3 on the coil pack, and between secondary coils, so I assume the coil pack is OK, but is there a way to test the coil pack using a battery on a spark plug to make absolutely sure it works? How do i test the control side to see if a signal is coming from the ECU?


Sun Apr 07, 2019 4:18 pm
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Joined: Wed Aug 11, 2010 9:27 am
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Location: Sheffield
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Post Re: Ignition wiring
If the fuel pump primes and the engine turns over the ecu relay must be energised as it controls energising the pump's relay.

The 5as imm works by killing the fuel pump.

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Mon Apr 08, 2019 3:16 pm
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Post Re: Ignition wiring
Tested using a 12v bulb yesterday and there isn't a signal to the coil while cranking. If the ECU isnt the cause a crank sensor might stop it starting. What else could I test?


Tue Apr 09, 2019 7:58 am
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Joined: Sun Oct 19, 2014 10:10 pm
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Location: Bristol
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Post Re: Ignition wiring
Might be a daft question but you never know...

Have you checked the inertia switch hasn't tripped? I imagine it would kill the fuel pump as well as the ignition but for the press of a big rubber button got to be worth a try?


Tue Apr 09, 2019 1:45 pm
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Post Re: Ignition wiring
There should be 12v to the coils and the ECU controls em by supplying the earth. I understand those early all-in-one coil packs are prone to failure.

Are the injectors working, crank it then remove a plug and give it a smell/is it wet?

Also cam sensor?

Are you SURE all the plugs are connected and in the right place?

So you turn the key, get the fuel pump priming, does the idle step motor make a noise too (should do when you switch off too) and the engine cranks but won't fire at all, no chuff of it trying or anything?

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Tue Apr 09, 2019 3:48 pm
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Post Re: Ignition wiring
I think you're on to something here. Theres no petrol coming through the injectors, the pump works but theres no petrol in the cylinders!

Does that take it back to an ignition switch issue?


Wed Apr 10, 2019 8:38 am
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Post Re: Ignition wiring
Simple stuff, is there fuel in the tank? Is there oil in the sump? Let the pump prime, switch off and then crack open the nut on top of the fuel filter (pressure release) does fuel seep out? if it does let it - to release any pressure and then tighten back up. Follow the fuel hose from filter to where it joins the metal pipe near the intake manifold and disconnect it - careful! you should have released any pressure build up by undoing the nut but you'll prob get fuel coming out, have container ready to catch it, wear gloves glasses etc.
Now hold this hose into a container and switch ignition on to make the pump prime, does fuel come out? It won't be a high pressure jet or anything and you won't get much, the pump should stop on it's own after few secs.

Assuming you get fuel, reconnect it all as we seem to be getting fuel to the injectors.

Do i need to remind you to be careful cos it's petrol?? :!:

Dunno if these will help.
http://www.tom-seven.stillgame.ch/wiki/ ... ing_wiring some good info.
http://www.tom-seven.stillgame.ch/wiki/ ... sensor_cas see the notes about measuring impedance.

Have you checked for an actual spark from one of the plugs while cranking?

https://blackbox-solutions.com/help/SM072.html

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Wed Apr 10, 2019 10:32 am
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Post Re: Ignition wiring
Thank you Sidewinder - those are some fantastic links.

I'll have a look at the petrol as you suggest.


Sun Apr 14, 2019 12:17 pm
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Post Re: Ignition wiring
Just another one, get some Ezi-Start spray into manifold whilst cranking, does it fire, if so it's sparking.


Sun Apr 14, 2019 3:59 pm
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Post Re: Ignition wiring
^^ V good suggestion.

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Sun Apr 14, 2019 4:07 pm
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Post Re: Ignition wiring
I do have petrol in the tank and oil in the sump. Checked engine timing and all lined up ok.There is definitely no spark and no injector pulses.

Decided to go back to basics - pull all the connectors off and check they're all ok. In the mean time I have purchased a new engine management relay pack, coil pack and ht leads (doesn't hurt to have spares even if they aren't the cause).

I've been around the vehicle and cleared up and identified the various earth wires (some were badly corroded) and tested for any high resistance wires and all seems ok.

Spot of lemon juice on sensors and contacts, cleaned with a soft brush and then cleaned off with contact cleaner spray (they sparkle!)

Tested sensor earths on pink black (all ok). Noted that I don't have an ambient temp sensor - I don't think this matters to the vehicle starting?

Went on to check all of the ecu wires for continuity and resistance around sensors. All seem ok.

Decided to check for earth continuity to make sure there are no shorted wires and I have noted that, on the white main feed from the ignition switch to the engine relay / ECM I do not have any continuity beep on the multi meter, but instead it spews out a load of numbers?! (Note battery positive, ECM and relay pack are not connected at the moment). When I switch to low resistance I am seeing around 80 ohms of resistance between the white ignition wire and engine ground.

As this is the power side of the system surely that means there is a short to ground somewhere in the wiring starting at the ignition switch to the ECM / relay pack ?

Next step was to re-connect everything and check for 5v around the sensors with everything cleaned up.


Mon Apr 15, 2019 5:14 pm
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