Ignition coils too far out of range?
 

Using Les Andrews's Vol., I am trying to eliminate coils as an issue with my car sputtering (but not while idling). I have three coils which all measure 6.3 volts +- to ground when installed.

The resistances of the coils are as follows: (the numbers are rounded off)

1. 8.22K ohms on both sides to the middle and 1.2 ohms between the plus and minus terminals.
2. 8.30K ohms on both sides to the middle and 1.3 ohms between the plus and minus terminals.
3. 11.60K ohms on both sides to the middle and 1.6 ohms between the plus and minus terminals.

According to Les Andrews, the coils should be 6.7K ohms to 10K ohms for both sides to the middle and 1.6 to 1.8 ohms between the plus and minus terminals. So all of my coils are out of range, either too low and too high .

Are there any potential issues with the coils based on these readings? Do I need to keep looking for a new coil? Coil 3 above is currently installed in the car.

Bill

Re: Ignition coils too far out of range?
 

If you are not using a proper coil tester then you have no idea what you have. You need to see what happens to the spark after the coil has warmed up.

Re: Ignition coils too far out of range?
 

I understand. Getting a coil tester is the best way. I don't have one and Les Andrew's test procedure in vol. 3 seems to be a good substitute.

So, where does one get a coil tester?


Bill

Re: Ignition coils too far out of range?
 

They come up on eBay from time to time. I've got one, I'd be happy to test the three of them for you if you want to ship 'em.

Re: Ignition coils too far out of range?
 

So, until I get a coil tester or have someone test the coils for me, how useful is Les Andrew's procedure on page 2-5, Model A Ford, Troubleshooting and Diagnostics?


Bill

Re: Ignition coils too far out of range?
 

Thank you for the offer. I may take you up on it.

Re: Ignition coils too far out of range?
 

A coil can appear fine resistance wise but fail in operation. I do not know numbers, but as a kid I was in charge of testing all the coils for selling at the flea markets. Something about making that blue arc.

Quite a few would work fine cold. Let them heat up and they died off. My guess is they would test fine resistance wise on a meter.

I also have some problems with measuring the resistances accurately. Most guys are not electronics savvy. It is easy to get wrong readings with a crappy meter, poor leads, or dirty connections. At these resistance values you can be off by quite a bit. So I would not always trust an average person to know if they might be getting a good reading. This is a comment from a person who does a lot of electronics troublshooting and has watched people do it wrong. Oh and the people doing it wrong in some cases were electronics engineers.

The only way to know if you have a good condensor or coil is with a coil condensor tester. Anything else is no better then a guess in the end.

Re: Ignition coils too far out of range?
 

So what you are saying is that the resistance readings in Les Andrew's book are an approximate guess or an indication, and not definitive.

A local Model A club mechanic told me that if the voltages are fine (6.3 V +-) at the appropriate places it should be all right.

So, where does it leave someone like me who does not have a coil condenser tester at their immediate disposal?

Bill

Walworth, NY

Re: Ignition coils too far out of range?
 

Bill, I see you are from Walworth, N.Y. where I went to grade school. Upstate N.Y. is beautiful, or it was back in the 50's and 60's.
I bought my condenser tester on Ebay about 20 years ago, but it got burned up in the fire, so I'll have to look for another one.
A good simple check for the coil primary is to connect it to a 6 volt battery charger with an ammeter, and when the 2 primary terminals are connected it should draw about 4 amps.

Re: Ignition coils too far out of range?
 

Hook a timing light up to the coil to distributor wire. Watch for constant even spark. If your engine runs you can drive it and watch,if not turnit over with starter. You will need 12 volts to power light,xtra battery
This will tell you if the coil is working.
John

Re: Ignition coils too far out of range?
 

The best way to test a coil is with an oscilloscope. It can be warmed up by powering it up like an electromagnet till its warm but not too hot. A function check should result in a nice blue spark if polarity is correct.

Most coil resistances of primary side checks should at least be within 10% of nominal 1.5 Ohm value. Heating up an old coil of unknown condition can result in open circuit when the wire expands and a crack opens up. An internal wire to wire short in a coil can reduce the resistance. A cracked wire can increase resistance and cause higher operating temperatures as well as intermittent opens after warm up.

Re: Ignition coils too far out of range?
 

I wonder if there is an inductance value for a good coil that would be useful?

Re: Ignition coils too far out of range?
 

Can anyone recommend a good, inexpensive coil tester?

Re: Ignition coils too far out of range?
 

Heathkit capacitor tester. https://www.ebay.com/sch/i.html?_fro...ecker&_sacat=0

Agree with your coil test. Then maybe heat it up and see what happens to the current draw??

Re: Ignition coils too far out of range?
 

Hantek digital automotive oscilloscopes are likely the least expensive types but I don't know how well they work. A lap top can be set up to work with some digital tooling like this but others are likely more expensive and most require a laptop computer. A person would need the inductive pickup cable too.

I've used an old Heathkit C3 but if you look for one, make sure it has the cables and the instructions. The old Heathkit ones also have old caps in them too. Some of the later digital types are relatively inexpensive but a person needs to make sure they get one that will check the range of caps they are testing.