Coil Confusion

Coil Confusion

Joined: July 20th, 2004, 6:25 am

September 25th, 2008, 11:11 pm #1

The coil on my carbed 1300 X is producing a pale yellow spark, so I think it's time for a replacement.

I have searched the archives here and read heaps about 12v/9v coil selection, but am still confused.

There is no ballast resistor on this spec car (well, I can't see one anywhere). This would lead me to believe I should be buying a 12v coil (Bosch GT40)

However, when I measure voltage at the positive coil terminal (ignition on, not cranking), I see 9v, which indicates I should be getting a 9v coil (Bosch GT40R).

Any ideas?

Regards,

Brian

Brisbane, Australia
1979 1300
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Colin Duckworth
Colin Duckworth

September 25th, 2008, 11:25 pm #2

You need the GT40 (not the 'R'). I'd be real surprised to find a ballast resistor anywhere in the system. Besides, it would have to be a PO that fitted one. If by chance you find one, take the bloody thing out of the loop. The 9V reading could just be indicative of a number of factors such as wiring length; battery condition . . . did you check the input voltage with the motor running? You might also contemplate installing a relay for the coil and rewiring to get 'real' voltage at it.

There are a few folk around the traps, too, who reckon the standard coil is the best thing to run. But, the swap to the GT40 is something I've done to all my Fiats over the years (except for the 132 I just got, 'cos it's sooo original) and I've found it a good thing to do.

Supercheap at Keperra, Sir. 10 minutes up the road (traffic pending, naturally) LOL

PS: are you guys up there doing anything on 23 November for the X 'anniversary'?
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Ian Lawson (NZ)
Ian Lawson (NZ)

September 26th, 2008, 12:28 am #3

The coil on my carbed 1300 X is producing a pale yellow spark, so I think it's time for a replacement.

I have searched the archives here and read heaps about 12v/9v coil selection, but am still confused.

There is no ballast resistor on this spec car (well, I can't see one anywhere). This would lead me to believe I should be buying a 12v coil (Bosch GT40)

However, when I measure voltage at the positive coil terminal (ignition on, not cranking), I see 9v, which indicates I should be getting a 9v coil (Bosch GT40R).

Any ideas?

Regards,

Brian

Brisbane, Australia
1979 1300
<<<<< The coil on my carbed 1300 X is producing a pale yellow spark,......>>>>>

Brian, I fully agree with Colin on this. Stick with a standard-type 12v coil (you may well find your present coil is OK, if you solve the following problems)

9 volts at the coil + wire (ign on, not cranking) is TOO LOW! That's probably the reason for the 'pale yellow spark'!
I have checked the voltage (same conditions) on my '78 1300, and have got 11.2 volts at the coil + wire.
Somewhere along the ign circuit, you are losing around 2.5 volts - could be the internal ign switch contacts (seems like the ign switches on our "beloved" X's are prone to high internal resistances as they get older).

I suggest running a temporary jumper wire from the 'hot' cable on the starter motor, up to the + connection on the coil (be careful of 'sparkies') and see if the coil performance improves. If it does, go searching for voltage loss somewhere along the switch-to-coil circuitry.

Have fun!!

cheers, Ian - NZ
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Joined: July 20th, 2004, 6:25 am

September 26th, 2008, 2:34 am #4

Lawso, Colin,

How do you interpret this...

If I take the wire off the positive terminal of the (new) coil and measure the voltage at the wire, I get 12v.

When I replace the wire onto the terminal and measure at the terminal, I get 9.5v.

What does this mean? Is it significant that I'm using a Lumenition system?

Regards,

Brian

Brisbane, Australia
1979 1300
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Joined: July 20th, 2004, 6:25 am

September 26th, 2008, 2:36 am #5

You need the GT40 (not the 'R'). I'd be real surprised to find a ballast resistor anywhere in the system. Besides, it would have to be a PO that fitted one. If by chance you find one, take the bloody thing out of the loop. The 9V reading could just be indicative of a number of factors such as wiring length; battery condition . . . did you check the input voltage with the motor running? You might also contemplate installing a relay for the coil and rewiring to get 'real' voltage at it.

There are a few folk around the traps, too, who reckon the standard coil is the best thing to run. But, the swap to the GT40 is something I've done to all my Fiats over the years (except for the 132 I just got, 'cos it's sooo original) and I've found it a good thing to do.

Supercheap at Keperra, Sir. 10 minutes up the road (traffic pending, naturally) LOL

PS: are you guys up there doing anything on 23 November for the X 'anniversary'?
Colin,

Following your valued advice, SuperCheap Keperra is now $59 better off.

They reckon the GT40 is no longer available and is showing on their books as $1 if any are in stock. No such luck.

GT40T is the same thing, but in the cubic sort of package rather than can-shaped.

See my response to Lawso.

Regards,


Brian

Brisbane, Australia
1979 1300
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Ian Lawson (NZ)
Ian Lawson (NZ)

September 26th, 2008, 4:45 am #6

Lawso, Colin,

How do you interpret this...

If I take the wire off the positive terminal of the (new) coil and measure the voltage at the wire, I get 12v.

When I replace the wire onto the terminal and measure at the terminal, I get 9.5v.

What does this mean? Is it significant that I'm using a Lumenition system?

Regards,

Brian

Brisbane, Australia
1979 1300
<<<<<Is it significant that I'm using a Lumenition system?>>>>>>

Brian, my 'auto electrical expertise' is OK up to about EH Holden level, mate!!

However, harking back to my 'ye olde' Engineering Trade school experiences, voltage in an electrical current = pressure; amperage = flow.

Therefore, with your scenario, when voltage is REDUCED following connection to a component, it means that the 'pressure' is being restricted somehow by that component.
Which makes me think that something in your Lumenition system is probably responsible for the voltage drop.

Hey, maybe Bob Brown, our X-head electrical guru, needs to chime in here!!

Good luck!!

cheers, Ian - NZ
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Colin Duckworth
Colin Duckworth

September 26th, 2008, 4:56 am #7

Lawso, Colin,

How do you interpret this...

If I take the wire off the positive terminal of the (new) coil and measure the voltage at the wire, I get 12v.

When I replace the wire onto the terminal and measure at the terminal, I get 9.5v.

What does this mean? Is it significant that I'm using a Lumenition system?

Regards,

Brian

Brisbane, Australia
1979 1300
. . . a function of the old V=IR (voltage = current X resistance) caper. So . . . 12v when it's off (no current draw / resistance) and 9.5v when it's on (coil's current draw? internal resistance?). It would be interesting to see what the voltage is at the point at which the Luminition says, "FIRE" and generates a spark (ie, what the voltage is when the 'points' are effectively open).

$59-00 is OK. This is for one of the black things, right? I think I paid up near $80-00 (at SuperChook . . . and at Keperra -- on my trip from hell a couple of years back now that I think about it) for one of the similar 'red' things. If I remember over the weekend, I'll carefully see what voltages I have across my coil. But, I run a MSD, so it could be meaningless.

How's the spark now though?

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Joined: July 20th, 2004, 6:25 am

September 27th, 2008, 6:08 am #8

Colin,

Bosch GT40T is one of the red jobbies.

It didn't help the spark situation - it's still the colour of Surfers Paradise sand. Perhaps there's a blue tinge to it if I squint really hard.

Maybe it's not a problem. I'm trying to track down a no-start-after-six-months-idle issue and I thought the plugs, while sparking OK outside the engine, may not be doing the job when under compression.

I'll move on to some other possible cause.

Regards,



Brian

Brisbane, Australia
1979 1300
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Joined: September 9th, 2005, 12:53 pm

September 27th, 2008, 8:56 pm #9

Yet another drawback with living in Canberra, Brian (and probably not just for me either) . . . I could probably pop over and diagnose that one for you in ten minutes.

OK . . . so you've got heaps of fuel? When you parked it, how much fuel was in the tank? If it wasn't much, you could appear to have fuel, but all it's 'octane' might have disappeared into the atmosphere (so it's a less volatile mix).

Does it make any effort to catch and run at all?

What sort of cranking speed do you have?
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Ian Lawson (NZ)
Ian Lawson (NZ)

September 27th, 2008, 9:55 pm #10

Brian, I also suspect a fuel problem!

How about dribbling a LITTLE fresh fuel down into the carby throat - hold throttle wide open when doing this!!

And then crank the engine over, holding the throttle open. If it starts to fart and spit a bit, at least you know that the ign is firing up!

cheers, Ian - NZ
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