Coil test readings

[joe912/62]

Tested my coil today and my readings
were primary .7 ohms and secondary .685 ohms.
Do these numbers look within range? It an 82SC

[HarryD]

Looks ok to me. Per my data: The coil Primary resistance should be 0.4 to 0.6 ohms, and the secondary is 650 to 790 ohms.

What's going on?

[joe912/62]

I just subtract the difference which I got when I touched the 2 leads together (.2)
That gives me .5 for the primary and .485 for the secondary.
Car won't start.

[HarryD]

No spark or no fuel? Lots of threads on this topic.

For fuel:
-Fuel pump running?
-Do you hear a squeel when you GENTLY lift the air plate in the fuel distributor?
-Can you get it to fire with a shot of starting fluid?

For spark:

You need to verify the basics.

Open distributor and check your points to be sure they are opening and closing when you crank.

To get a spark to the spark plug in the engine, several things need to happen. First, you need power to the CDI. Next you need to have a way to trigger the CDI (the points do this by opening and closing). Then the CDI will then send a pulse to the coil which will increase the voltage and send it through the high tension lead to the rotor and to the selected spark plug. You need to verify that each step in this chain is working.

1) Verify that the CDI is getting power.

2) Verify that the CDI is producing power to make a spark. You can do this with a "telegraph" test. Take the high tension lead off of the center of the distributor and put a spark plug on it. Ground the threaded part. With your plug attached to the center lead, open the distributor, remove the rotor, place your key in the run position, and manually open and close the points. Each time you cycle, you should see a spark from the plug. If you do not, you may have a bad CDI. Or Coil.

3) Verify that the coil gets a signal when you crank. Replace the rotor and distributor cap. Leave the plug on the center high tension lead. Crank the engine. Do you see a spark? If so, you are getting spark to the distributor. If not, your point gap may be off or there is some other problem with the connections.

4) Verify that the spark goes to the spark plug wires. Reattach the center lead to the distributor. Attach you spark plug to one of the leads going to the cylinder spark plugs and ground. Crank engine. If you see a spark you may have a timing problem. If no spark, you have a problem with your rotor or distributor cap or your wires are improperly seated.

[joe912/62]

It's an 82 doesn't have points

[PeteKz]

Joe, your numbers are not right. Please verify what you measured in ohms, not K-ohms. I also don't know what you mean by, "subtract the difference." You should measure the primary and secondary separately.

[John2244]

I checked my coil last week in my 1977s with a 3.0 sc engine. Primary was .6 ohms and the secondary was 710 ohms.
This was one of my checks for a no start condition. Turned out to be a faulty fuel pump.

John.

[PeteKz]

Thanks for the resolution follow up.

[HarryD]

Originally Posted by joe912/62

It's an 82 doesn't have points

Hmmm. You will need to search here to find how to test your distributor to be sure you are getting a signal to the CDI and coil.

[joe912/62]

I'm making allowance for the accuracy or inaccuracies of the my multimeter by getting a reading when I touch the test leads together

[joe912/62]

What coil would I need with this Permatune CDI?

[David Inc.]

I ran into a no-start and had some good feedback on testing the CDI and coil, worth checking the thread: Rebuild - No Start (No Spark)

My issue was totally separate, and with a permatune CDI I'm really not sure how to start.

Edit: For what it's worth my coil resistances were .9 and 900 ohms, runs fine. Issue was in the green wire.

[HarryD]

Is the issue No start or dies after a while?

Permatunes have a history of failing. Can you borrow a known good one to test?

[mysocal911]

Originally Posted by David Inc.

I ran into a no-start and had some good feedback on testing the CDI and coil, worth checking the thread: Rebuild - No Start (No Spark)

My issue was totally separate, and with a permatune CDI I'm really not sure how to start.

Edit: For what it's worth my coil resistances were .9 and 900 ohms, runs fine. Issue was in the green wire.

Common problem/failure, especially with electronics enclosed in a Bosch casting.

[joe912/62]

What options do I have to replace one?

[HarryD]

Originally Posted by joe912/62

What options do I have to replace one?

Find a used unit, get a parts klassic replacement unit, or go to something like a MSD unit.

Before you do anything, get your hands on a known good CDI to verify yours has failed. Where are you located? Add it to your profile. Someone near you may be able to help.

[joe912/62]

Just re checked my coil, my multimeter has an auto range so I get .7 ohms for primary and the meter switches to Komhs when I test the secondary. Reading is .690 which would be 690 ohms so the coil test good. Sounds right?

[PeteKz]

Yes. Primary at 0.7 ohms is a little high, but that's not what would cause a starting problem, and may be due to your meter inaccuracy. Also it's difficult to get good measurements at low resistances because any crud on your probe or the surface you stick it to will affect the reading. Press harder and it may go down to 0.6. Also, check the primary resistance by measuring from the plug that goes into the CDI to make sure you don't have high resistances or broken wires in between the CDI and the coil. Otherwise, try swapping a CDI box.

I didn't see an answer to the question, "did you check for spark?" I presume that's your problem, but you didn't verify it.

[joe912/62]

What is an easy way to check for spark? I have the metal covered spark plug wires with the metal ground straps. I tested the resistance of a few plugs and got 4.05 k-ohms but I'm not sure I'm doing it right. I tested them while they are in the car and still grounded.

[PeteKz]

Pull one plug wire off the plug. #4 is easiest to get to. Put another spark plug in the cap, and ground it against the engine or car. Have someone else crank the engine and see if it gives a strong spark. If you don't have a spare spark plug, then remove the plug from the hole too and use that.