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intermittent ignition fail


simon a-b

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Simon,

 

 would find a good auto electrical guy near you and ask the question. You should get answers without annoying him too much. Once he sees the car you may get some help for nothing up front. Everywhere I have taken my car I have been looked after pretty well. :)

All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

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The coil would get pretty hot in use. If you can grab it for a few seconds I would think its not too hot.

 

I dont get this "adjustable resistor", are you sure its measuring correctly. Could you not get a normal one like this: 

 

http://www.rimmerbros.co.uk/Item--i-134176A

 

Any car electrical supplier should have lots of them.

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That pic, Andy, is pretty much exactly what I've got.  If you look underneath, you'll find a loose spring type coil of nichrome wire between the two terminals.  The ceramic block acts as a heat sink. 

The longer the wire, the higher the resistance.  I just trimmed the wire, refitting it to the terminal posts each time until I got an indicated 6.5v across the coil. 

 

As for the heat, I think you're probably right.  I've got a spare coil, which I'll pack in the toolbag, along with the required tools to swap.  This will ensure that the coil will never fail!   :fun:

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  • 1 month later...

So a quick update.  I messed around with the ballast resistor, adjusted it to get a good 6-7v across the coil when running, and battery voltage when cranking.  It's important to test the voltage across the coil when the ignition is on but not running, the coil will give spurious results on a meter while it's doing its thing.  

Anyway after a lot of messing around, I also found a leak on the rear carb, and fixed that.  This revealed a leak from the pump (now that it wasn't coming out of the carburettor!), so when all these were fixed up I was good to go.  

All went well until I decided I'd put the ignition kit back in its little box, whereupon the very same gremlins came back.  

So it was pretty clear that it was related to one or more of the connections were the problem.  I went over the lot again, tightening up female spade connectors, checking for any dodgy connections, and all is well again, with the added bonus of not spewing fuel over the distributor, or out of the side of the pump onto the road!

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  • 6 years later...

Simon and other gents. I've had a interesting read with this thread. My S2 does have some intermittent failures that relate to heat since ages. When heated up on a summer day, the car suddenly misfires, runs just on a few cylinders, doesn´t reply to any throttle and finally dies before misfiring with a very loud bang. I had addressed these failures before to being fuel related, had found lots of crap in the fuel pump before, so replaced it for a "Mitsuba" one which is using an extra internal filter. Found lots of rusty crap again in the pumps fuel filter after a while, so this time I changes the tanks completely for new aluminium ones including all new vent hoses and stuff. But: the failure remained. So this time I thought it must be ignition related. Tested the Luminition modules as explained in the manual and changed the optical switch for a new one. No effort. So I diagnosed myself into a head gasket failure, because at the same time I there was water disappearing and I clearly couldn´t find any leaks. The test fluid to find out about CO2 in the expansion told me I have some exhaust fumes in the water, so I pulled the head. In the end I did a complete head and bottom engine overhaul together with all new cooling pipes and hoses. After that I thought the failure is cured as I managed to drive about 150miles without having to call any road assistance since years. Until the day before my holdiday-trip in the Esprit should have started, when I had the exact same symptoms as before including the end with the very loud misfire bangs. Coil was hot, directly after the failure, but not too hot to touch. I wanted to diagnose the coils condition and if it's the right type. The coil is being replaced before and is now a 3Ohm for unbalasted use. In case my car would still have a balast resistor, where would I find it?

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  • 2 weeks later...

ok, further investigation has been made. And I think I've understood the idea and difference of ballasted and non-blasted ignition coils now. Still there are a few things I don't quite get. My car has a Lumenition fitted, but according to SJ-Steve this must have been done afterwards on a 79 S2 Esprit. So I don't know if it has been done right by the previous owner. What I can tell is, I have a supective red wire coming from the bulkhead that connects to the + of the coil. That wire is not within the loom and seems to have been fitted afterwards. I couldn't find out yet where it connects to on the other side. Measuring what voltage that wire carries leaves some more questions now. When I connect the wire to my multimeter (black wire of the multimeter is connected to a good ground) it shows 12.5V with ignition switched on. But only while I leave it disconnected from the coil. As soon as I connect the red wire to the + of the coil, the voltage it carries drops down (immediately) to 8.22V. Disconnect it from the coil: 12.5V again. Then there is a second wire connected at the + of the coil. That yellow/white wire connects to the solenoid and is only carrying power when cranking. I think I understand what this is for (support cold starting in a ballasted system with a 1.5 Ohm coil) and it seems to be ok the way is is. But instead of 12V it carries 9V while cranking. I'm not so concerned about that, as it is anyway not essentially necessary to have and also the voltage dropping to 9V while cranking might be normal. What I find more susceptive is that red wire with the sudden voltage drop as soon as I connect it to the + of the coil. Can anyone explain what's going on?

I did one further test. I drew a new cable from the plus of the battery to the coil (have fitted a kill switch years ago so I was able to disconnect power after a while). That new cable is without any doubt missing any ballast resistor or "resistive wires", I carries 12.5V from the battery. When I connect it to the + of the coil that voltage does not drop. It stays at 12.5V.

So: is there a restive wire or ballast resistor hidden somewhere between the other red wire and the ignition switch? But then: why does it carry 12.5V as long as it is not connected to the coil and when it is the voltage drops to 8.22V?

Edited by marode
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I think you have confirmed everything is working, the red wire is a resistive wire. 

The resistive wires usually can be identified as they have a kind of woven insulation rather than plain plastic. Does it have this?

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4 hours ago, marode said:

. I think I understand what this is for (support cold starting in a ballasted system with a 1.5 Ohm coil) and it seems to be ok the way is is. 

Correct, the idea being that feeding a 6 volt coil with 12 volts produces a bigger, fatter spark in order ro aid starting. The downside is that the coil doesn’t tend to last as long as a 12 volt coil. :thumbup:

Cheers,

John W

http://jonwatkins.co.uk

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Thanks people! Andy gave the important hint. It must be the resistive wire when. It has the woven insulation (on top of its red plastic one) and inside it's sort of a steel core instead of a copper wire. I just dont´t quite get why this wire alone (just connected to the multimeter) is carrying 12.5V and connected to the coil it's 8.22V. But Anyway, the conclusion is: the 3Ohm coil is the wrong type for the car. I guess when it heats up it´spark is becoming even weaker so the car finally cuts out. Can anyone confirm this theory? Should I opt for a new flamethrower 1.5Ohm one?

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26 minutes ago, marode said:

 I just dont´t quite get why this wire alone (just connected to the multimeter) is carrying 12.5V and connected to the coil it's 8.22V.

Because of Ohms law.

V = IR

Voltage drop = current x resistance.

Without the coil connected, current is zero hence voltage drop across the resistive wire is zero.

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