202 Ignition Coil Resistance Specifications

[David L.]

Recently I bought a 7 function multi tester. Using the web I found out how to test an ignition coil which was quite easy. My original embossed "202" ignition coil tests 2.4 ohms for the primary winding (+ and -) while the secondary winding (+ and the coil output) tests 11,000 ohms. I have a second "202" coil from a 1966 Chevrolet and the test results are quite similar, 2.2 ohms and 11,100 ohms.
Do these coils meet the specifications of a good 1115202 ignition coil? I am a civil engineer, not an electrical engineer.

Dave

[Duke W.]

Re: 202 Ignition Coil Resistance Specifications

...sounds about right... 202 specs are in the '65 Corvette Shop Manual Supplement, later CSMs, and AMA specs. I don't have these, but someone who does should report. I believe the 202 coil was used from '65 thru '74 on single point distributors. HEI replaced the single point system in '75.

Duke

[David L.]

Re: 202 Ignition Coil Resistance Specifications

...sounds about right... 202 specs are in the '65 Corvette Shop Manual Supplement, later CSMs, and AMA specs. I don't have these, but someone who does should report. I believe the 202 coil was used from '65 thru '74 on single point distributors. HEI replaced the single point system in '75.

Duke

Duke,

I never thought to look in my 1966 Chassis Service Manual. In the Ignition Systems section (Ignition Coil Check - Breakerless) it states that the primary resistance at 75 degrees should be between 0.35 and 0.55 ohms and the secondary resistance at 75 degrees should be 8,000 to 12,500 ohms. My 1969 manual states the same.
Based on this it seems that both my "202" coils are out of the range for primary resistance (2.4 and 2.2 ohms) but within the range for the secondary resistance (11,000 and 11,100 ohms) as the temperature in my basement is about 68 degrees.

It seems odd that both my "202" coils test about the same. Is my $5 multi tester from Harbor Freight inaccurate? Do I somehow have to calibrate my multi tester?

Dave

[Leif A.]

Re: 202 Ignition Coil Resistance Specifications

David,
Prior to checking the primary resistance on your coil, did you calibrate your ohm gauge?. If yours doesn't have an adjustment, you can touch the two probes together and see what the reisistance reading is and then you can minus that number from your readings when you test the coil. The readings in this range are very sensitve and can be off by quite a bit...my gauge is always off a bit in this range. When reading the secondary it is not necessary to calibrate at the range is so high. Both my 202 coils mimic what you're finding.

[David L.]

Re: 202 Ignition Coil Resistance Specifications

David,
Prior to checking the primary resistance on your coil, did you calibrate your ohm gauge?. If yours doesn't have an adjustment, you can touch the two probes together and see what the reisistance reading is and then you can minus that number from your readings when you test the coil. The readings in this range are very sensitve and can be off by quite a bit...my gauge is always off a bit in this range. When reading the secondary it is not necessary to calibrate at the range is so high. Both my 202 coils mimic what you're finding.

Leif,
Thanks for the tip. When I set my multi tester on 200 ohms and I touch the two probes and then I read about 1.6 to 1.8 ohms as the numbers jump back and forth. Therefore using 1.7 ohms as the average my primary readings on my "202" coils would be about 0.7 and 0.5 ohms, which is close to what they should be. Maybe a more expensive tester would give me more accurate results. I guess that I should have read the instructions for my bargain basement multi tester.

Dave

[John L.]

[Duke W.]

Re: 202 Ignition Coil Resistance Specifications

Duke,

I never thought to look in my 1966 Chassis Service Manual. In the Ignition Systems section (Ignition Coil Check - Breakerless) it states that the primary resistance at 75 degrees should be between 0.35 and 0.55 ohms and the secondary resistance at 75 degrees should be 8,000 to 12,500 ohms. My 1969 manual states the same.


Dave

Those specs sound like they are for the TI coil, but the manuals should also have specs for the single point system coil, which should be the 202.

I have several of those Harbor Freight multimeters. I think most I got free with a coupon. They're okay to general work, but may not be that accurate and very low resistance values. Make sure the terminals are clean so you get a good low resistance connection with the probes. Check by shorting the probes and the meter should read very close to zero.

I don't think those meters have a calibration wheel like the old analog meters, but the 9V battery needs to be in good shape, and I think the display has a low battery indicator. I know I've killed a couple due to leaving the switch on, and it was easier to just get another free meter with a coupon than replace the battery.

Duke

[John L.]

Re: 202 Ignition Coil Resistance Specifications

David
Coil 1115207 = primary .38-.51 Ohms
Secondary 8200-12400 Ohms
Coil 1115202 = primary 1.24 - 1.46 Ohms
Secondary 6500-9500
After an on the road ignition failure last year - I checked both my original 55 year old 202 and a new one for back-up that I got from the mail order place and was surprised that they were both in spec. And that free junky multi-meter is now in the back-up box. If I had any multi-meter with me I could have kept up my 50 year old record of the car always making it home.

[David L.]

Re: 202 Ignition Coil Resistance Specifications

David
Coil 1115207 = primary .38-.51 Ohms
Secondary 8200-12400 Ohms
Coil 1115202 = primary 1.24 - 1.46 Ohms
Secondary 6500-9500
After an on the road ignition failure last year - I checked both my original 55 year old 202 and a new one for back-up that I got from the mail order place and was surprised that they were both in spec. And that free junky multi-meter is now in the back-up box. If I had any multi-meter with me I could have kept up my 50 year old record of the car always making it home.

John,
Are these specifications from the 1965 Chevrolet Service Manual?
BTW, do you live in NH?
Dave

[John L.]

[Richard G.]

Re: 202 Ignition Coil Resistance Specifications

Just expounding on the information Duke already posted.

Low resistance is very difficult to measure accuracy.
I believe this is one of the reasons the Corvette coil resistance and primary resister measurement comes up so often.
As an example of how low the measurements are it would be the equivalent to measuring the resistance of a 220 foot long piece of 18G wire. (It is 1.4 ohms).

A low resistance measurement is typically defined as a measurement below 1.000 ohms. However, most multimeters aren't accurate below 1 ohm, and some can't even measure accurately below 10 ohm.

As you can see coils primary resistance values are getting close or well into the the LOW range depending on the coil you are checking. Terminal connections and lead resistance and temperature all play an important part in getting this measurement. This is why a temperature specification is given in the service manual. Meter drift (when the leads are connected together) is likely the changing resistance at the clips or just a poor meter design or low battery as Duke suggested. If the meter is drifting you will not be able to accurately measure low resistance without finding the cause first.

Their is just a lot of variables that need to be accounted for at these low resistance level.
Rick

[Russ S.]

Re: 202 Ignition Coil Resistance Specifications

!973 used the 270 coil. I would expect 1974 also used the 270.

...sounds about right... 202 specs are in the '65 Corvette Shop Manual Supplement, later CSMs, and AMA specs. I don't have these, but someone who does should report. I believe the 202 coil was used from '65 thru '74 on single point distributors. HEI replaced the single point system in '75.

Duke

[Tom L.]

Re: 202 Ignition Coil Resistance Specifications

IMHO, the best tool to determine resistances for values that low would be a a good old school Simpson meter if you know someone that has one. I no longer have one but the are not uncommon.