Technical replace coil?

[lycraman]

Hello-
I am fast approaching the end of my tether- I hope that someone can help me! I have a 500L with a 650cc engine. Several years ago, it would run fine until it got hot when it would misfire for 20 seconds or so before stopping. Once it had cooled, it would restart. I tried changing coil, condenser, distributor cap, points, rotor arm and HT leads. This
seemed to fix things, but not for long. When I last tried to use it I replaced the condenser again, which seemed to cure it. However, I now have a very weak spark and can't start it at all. You may have by now realised that I am utterly clueless about car electrics! I have read somewhere that a Bosch "blue super coil" might help, perhaps together with a ballast resistor? If so, could someone explain to me (in layman's terms) how a ballast resistor is connected? My coil is giving me a reading of 9.43Ω across the secondary windings using the 20KΩ scale, and 6.3Ω across the primary with the 200Ω scale.
Any help would be gratefully received!

 

[fiat500]

Hello-
I am fast approaching the end of my tether- I hope that someone can help me! I have a 500L with a 650cc engine. Several years ago, it would run fine until it got hot when it would misfire for 20 seconds or so before stopping. Once it had cooled, it would restart. I tried changing coil, condenser, distributor cap, points, rotor arm and HT leads. This
seemed to fix things, but not for long. When I last tried to use it I replaced the condenser again, which seemed to cure it. However, I now have a very weak spark and can't start it at all. You may have by now realised that I am utterly clueless about car electrics! I have read somewhere that a Bosch "blue super coil" might help, perhaps together with a ballast resistor? If so, could someone explain to me (in layman's terms) how a ballast resistor is connected? My coil is giving me a reading of 9.43Ω across the secondary windings using the 20KΩ scale, and 6.3Ω across the primary with the 200Ω scale.
Any help would be gratefully received!

What sort of ignition coil is fitted at present? The 6.3 sounds wrong.

 

[Goldnrust]

9.3kΩ across the secondary winding sounds perfectly reasonable to me? Likewise the 6.3Ω across the primary isn't too far of the mark either.

Some coils have a lower resistance across the primary winnings (approx 1Ω) and they requite a ballast resistor to be fitted between the coil and the 12v source in order that the coil does not burn itself out. Running the low resistance coils without a ballast resistor will damage them, and running a normal coil with one would produce a low power spark, they are not in themselves a performance improving device.

That does not read to me like it's necessarily coil issue that you're having. Weak spark, as opposed to no spark, would have me looking at the condenser and points first. I would first check the points gap and clean the points. I would also check you've got a good ground between the engine and the chassis. I would also check there is a good 12v coming to the coil and that there is good continuity in the wire that runs from the points to the coil. Thats the free and easy stuff.

After that I would suggest trying a new condenser, they are known to fail on 500s and are pretty cheap and easy to swap out. They are also of variable quality, I myself have experience condensers failed from new out of the box...

 

[lycraman]

Hello- thanks for your responses. Attached are a couple of snaps showing the coil. I will certainly try another condenser, but the one that is on it at the moment is brand new. In the past, fitting a new condenser has only ever seemed to be a short term fix. Without wishing to seem too thick, how do I check for 12V coming to the coil? Thank you!

 

[fiat500]

9.3kΩ across the secondary winding sounds perfectly reasonable to me? Likewise the 6.3Ω across the primary isn't too far of the mark either.

Some coils have a lower resistance across the primary winnings (approx 1Ω) and they requite a ballast resistor to be fitted between the coil and the 12v source in order that the coil does not burn itself out. Running the low resistance coils without a ballast resistor will damage them, and running a normal coil with one would produce a low power spark, they are not in themselves a performance improving device.

That does not read to me like it's necessarily coil issue that you're having. Weak spark, as opposed to no spark, would have me looking at the condenser and points first. I would first check the points gap and clean the points. I would also check you've got a good ground between the engine and the chassis. I would also check there is a good 12v coming to the coil and that there is good continuity in the wire that runs from the points to the coil. Thats the free and easy stuff.

After that I would suggest trying a new condenser, they are known to fail on 500s and are pretty cheap and easy to swap out. They are also of variable quality, I myself have experience condensers failed from new out of the box...

I'm not sure about that:

Hello- thanks for your responses. Attached are a couple of snaps showing the coil. I will certainly try another condenser, but the one that is on it at the moment is brand new. In the past, fitting a new condenser has only ever seemed to be a short term fix. Without wishing to seem too thick, how do I check for 12V coming to the coil? Thank you!

There should be a (probably) blue wire, maybe with a tracer colour, that you connect to terminal 15 (+). Remove that and check with the voltmeter between it and a good ground, with the ignition switched on. It should give 12 or slightly more volts unless someone has stuck a resistor in somewhere, which could be the problem.

Obviously, the other terminal carries a wire to the distributor low-tension stud where the condenser is also secured.

I do think that type of coil, in your setup, should read 3 ohms across the LT terminals.

 

[Goldnrust]

I agree 3 Ohms would be better, but as 6 Ohms is neither short circuit or 10/100x the normal value, it wouldn’t personally suggest that’s the key problem? Yeah

 

[fiat500]

I agree 3 Ohms would be better, but as 6 Ohms is neither short circuit or 10/100x the normal value, it wouldn’t personally suggest that’s the key problem? Yeah

I agree, maybe not the cause of the problem, but I wonder why that figure seems to be repeatedly specified wherever a non-ballasted "traditional" points and condenser setup is standard issue. It's cropped up on the Forum before now as a discussion subject.

 

[the hobbler]

I agree, maybe not the cause of the problem, but I wonder why that figure seems to be repeatedly specified wherever a non-ballasted "traditional" points and condenser setup is standard issue. It's cropped up on the Forum before now as a discussion subject.

When a "Bosch Blue" coil is fitted, a ballast resister is NOT required. When my engine was on points I used a "Bosch blue" and a competion condenser from Swiftune (an alternative is Shacktune--they look identical) and mounted the condenser up by the coil. But don't forget, you will still need a lead from the distributor to the negative side of the coil. By doing this, the condenser is removed from the heat of the 'cooling' air from the engine.

 

[fiat500]

When a "Bosch Blue" coil is fitted, a ballast resister is NOT required. When my engine was on points I used a "Bosch blue" and a competion condenser from Swiftune (an alternative is Shacktune--they look identical) and mounted the condenser up by the coil. But don't forget, you will still need a lead from the distributor to the negative side of the coil. By doing this, the condenser is removed from the heat of the 'cooling' air from the engine.

My point is that a "standard" Fiat 500, as far as I know, in common with most, straightforward classic cars of its era, needs a basic, 3ohm coil. From my own experience, the Bosch blue coil, when correctly sourced, is an excellent alternative to the original.

Personal experience tells me that in the late 60s at least, the "Klitz" coil was standard fitment, not the expected "Magneti-Marelli"; I have measured several of those and as with the Bosch, they are 3 ohms across the LT terminals. 6 ohm coils are available and my internet inquisitiveness peaked out when I found that they are fitted to some Ferraris but that a resistor should also be used with them.

It is hard to find the spec for the BK2A but from the wide fitment recommendations I suspect that it is in the range based on 3 ohms. I don't understand electricity sufficiently to know how the differing resistances affects the creation of a spark other than that some highly engineered, fast-revving, multi-cylinder engines may have a very short dwell time in which to generate a spark , but clearly, the choice of component was not at random in the original spec. Fiat 500.

ignition coil | FIAT 500 (Classic)

Hi all. I'm looking at replacing my tired old ignition coil (KLITZ brand - 20 years old or more??) Don't laugh as it's been pretty good. I had replaced it with a brand new marelli BK2A (apparently made in PRC) and within 30 minutes it crapped itself! Anyone had any luck with other brands or...

www.fiatforum.com

 

[bugsymike]

My "ten pence worth" for what it is worth, if condensor at fault or suspect, contact points usually go blue and pitted, in which case always change points as well as condensor, correctly gap them and I personally put a small amount of high melting point grease on the heel where it touches the distributor cam otherwise the fibre heel quickly wears down and closes the points giving more breakdowns.
A lot of issues with older systems is the quality of "pattern" parts available today and has been mentioned some do not even work out of the box.
I like the idea of the Bosch Blue coil mounted away from the heat along with the condensor, many times I went out to breakdowns as an apprentice found the condensor was at fault and not having the correct one in the van was able to swap the radio suppressor/condensor that was fitted on the switch side of the coil over the the CB contact breaker side, snip off the old condensor, clean and reset the points allowing the customer to drive back to garage to be fixed permanently.
On ballast resister type coils where fitted on Vauxhall Vivas etc.it was I think a 8 volt coil with the ballast resister bolted to the terminal with an extra wire, the idea was on cranking the 8 volt coil was supplied with battery 12 volts which may have dropped during cranking, but then when starter was released the 12 volt supply then went through the ballast resister to happily run the 8 volt coil.
Apart from where coils are shorting HT voltage down the neck of the coil giving a misfire which is often visible or if you have a good heart can be checked by running your hand around the area , Coils rarely totally fail, I can only recall personally one in 50 odd years and that was on a Mk 3 Zephyr four cylinder and was a break in the internal wiring which could be duplicated by giving it a belt with the back of your hand.
Many car electrics issues on older points based vehicles are caused by having the ignition on whilst checking something else and engine not running, this quickly results in the coil and condensor overheating, to the point I have seen oil running from the coil and hot to the touch, leaving ignition on also burns the points as well. So if you have to have ignition on to do some other job all you need to is pull the CB points side wire off the coil to prevent damage.

 

[lycraman]

Thanks for your input everyone- I'll see how I get on...