Ignition coil ohms?

So my car won’t start. The short of my problem is the ohms on three coils that are suppose to be for my car don’t add up to each other or the book. here’s the story…

Its a 1986 Sabaru GL. OHC. 1.8L Carbonator w/ no turbo 2WD.

Car dies. Many hours later (the next day) it starts back up but only runs for 10 minutes and dies again. So we notice there is no fire aka electricity from the secondary plug of the ignition coil to the distributor cap. So we feel the ignition coil and its hot. We don’t have a multi-meter to check it so we just buy a new coil. The new one has a broken terminal so we have to wait until the morning to exchange it. Next morning car starts right up but again dies after a few minutes (less time this time). So we think, maybe we got a bad ignition coil. So we buy a new one from another auto parts store. So now we have two ignition coils because the original one we told Auto Zone to toss. So this one fire’s up and dies within seconds of firing. So we obtain a multi-meter because my book on the car says you can test the ignition coil by ohming it out. (i should add we also bought a new rotor, distributor cap, and all new cords because the car needed it anyways).

There is where i get lost…

The book says it should be between 1.13-1.38ohms primary resistance. Well the one coil is 1.8 and the other is 1.2. So neither fall within the range on the book. So are they bad? don’t know… I go to NAPA (a third auto parts store) and the coil they want to sale me has a reading of 2.2. So three coils. All match up to what is suppose to be in my car. All three have a different ohm reading and non of them fall within the range specified by my book. So whats the deal? i don’t get it?


So the book says to test the pick-up coil after this. It is suppose to be between 130-190 “ohms”. Well mine reads 5.6 ohms. HOWEVER. it does read 142 k-ohms. This throws me off because that’s in the range but its “k-ohms” and not just “ohms” So is this part bad or not? i don’t know because the ignition coils are way off from the book. The pick-up coil is $300 so i don’t want to just buy it on a whim.


Final problem. So the car used to start and run for a minute at least after a long enough time. Now it doesn’t start at any time… the battery still reads 12.16V volts, so its above the 12.7v mark… i fear the worst… please help…

I think you may be misinterpreting the readings. For example, in your post, you say one of the coils reads 1.2 ohms. This reading is within the range of 1.13-1.38. Another way of putting it is: 1.20 ohms, which is higher than 1.13, but less than 1.38. See?

Also, 12.16 is less than 12.7 (12.70) volts.

When using a digital ohmmeter, you must be careful to not touch the electrodes as you can put your own body resistance in parallel with the circuit you are testing which can skew the readings. Be sure you have a positive electrical contact, especially when measuring small resistance values since a poor connection with the meter’s test leads can significantly skew the result.

You must also disconnect anything you are testing. If a device is connected to something, you will not get an accurate reading.

Finally, before taking any measurement, but especially very low resistance measurements, measure the resistance of the test leads themselves by touching the ends of the leads together. You should get a zero reading, but on a very low resistance scale, you may measure a small resistance in the leads themselves. This internal resistance must either be adjusted out to get a zero reading, or if there is no adjustment, subtract the residual test lead resistance from the reading you get from the circuit under test.

If the readings in your post are accurate, you have at least one coil within the specification, (1.2 is within range) but the readings you report on the pickup coil don’t make any sense. “k-ohms” means “thousand-ohms”. If you’re reading 140K (thousand) ohms, that would tend to be an high resistence or open circuit, but if you are reading 5.6 ohms, that would indicate a short circuit.

Measure it again after checking the resistance of your leads, disconnecting the coil you want to test, and by not holding onto the contact ends of the meter’s test leads with your fingers. Let us know what you find.

The reason the coil got hot was due to the current running through it and the ignitor, which fires the coil. It sounds to me your ignitor is going bad after it warms up so I recommend you try changing it.

The small resistance differences you saw from the specs on the primary side of the coil are not too much to worry about since they can vary. You proved the coil worked at least when you first started it. Don’t let the coil get too hot as that can damage it. Changing the ignitior should keep that from happening. I am not sure if the original coil had a resistor built into it or not.

Thanks for the replies,
i am at work for now but i’ll re check the readings when i get back. I just kind of guessed on what the coils/pick-up coil ohms read. I didn’t write them down after i measured them. I don’t know much about reading multi meters though, thats for sure. or cars for that mater. I just know my car won’t start, and i need it to.

In my car my ignitor/ignition module is hard wired in with the pick-up coil. Under the distributor cap. so it is all sold as one($300) part. and that is the part i’m trying to test but i guess i need to re test it since that other guy say’s my readings don’t make any sense. I’m worried becuase the car doesn’t start at all anymore. so i wonder if i’ve jacked something else up checking and replacing all this other stuff.
1.So would the battery being 12.17 be too low to start it at this point or is that still enough?
2.Would this ignitor cause it to not start at all anymore? because it went from at least starting at first to never doing anything now.
4.You say not to worry about the ohms not matching the book on the ignition coils. thats what this other mechanic guy told me too. but i don’t get. why does the book give a range and say “replace the part” if it doesn’t fall within this range if coils are all different and it doesn’t matter anyways… how do i know if i have a bad coil then?
I’ll get the exact ohm measurements later today…

The car’s ignition system will still start the car with a low battery voltage. It is the starter motor you need to be able run and a low battery may not handle the load. I recommend you charge the battery up with a charger.

A bad or intermittent ignitor is a fairly common trouble and will certainly cause these problems you are having. That is why I recommended you replace it. It is the device that switches the coil current on and off to generate the high voltage. It may be mounted on the disty shaft.

To check the coil operation remove the high voltage coil lead from the disty and place it within a half inch of ground. Remove the wire from the minus side of the coil. With a jumper wire tied to ground then touch and remove the other end of the wire to the minus contact of the coil while the ignition is ON. Use a glove if you use your fingers to hold the wire so you won’t get shocked when you remove the connection. You should see a good spark when you remove the connection. Do not leave the wire tied to the minus side of the coil. If the coil makes a spark it should be ok.

I presume you have a different coil installed than the original one so it should be ok. One thing that could happen is the coil windings could be opening up after it has heated up. If that is the case then the resistance will be real high or infinite.

Hey, i did what you said and i have the exact numbers on my readings
Ignition coil: Primary: 1.7 ohms (out of range) Secondary: 10.64kohms (in range)
Pick-up Coil: 145.6 k-ohms, “Infinity” ohms, and 0.957 M-ohms. book says 130-190 "ohms"
Battery: Still 12.17 ohms

so if the pick-up coil is suppose to be 130-190 ohms and i get a reading of 145.6 k-ohms then this is out of range and the part is bad… no???

If the specification is for 130 to 190 ohms and the actual resistance is 145K ohms, I would call that bad and replace the part.

If you are truely reading 145,600 ohms then that is bad. I would be suspicious of any readings over 20 percent of the specs. So something that is 1000 times the rated spec is way off what it should be.

Sometimes, ohms are nonsense. Sometimes the book is the same. It shouldn’t be that way in a perfect world. An igniter is expensive but sometimes causes this problem. More than sometimes. With three coils, your engine would keep running if one was bad. So, you are getting a definite maybe for an igniter but the vehicle is well into the age where it will fail, if you have an igniter. I think you do.

First, taking resistance readings of a coil is difficult at best as coils have a reactance to them. You have to wait until the current stabilizes to get a good reading and this can take some time.

Next, the source of your problem may not be electrical, it could well be mechanical. You need to check for excess play in your distributor shaft. The best way to do this is to remove the cap and rotor. Turn the engine until one of the vanes lines up with the pickup coil. There should be a gap of about .010" Generally you need a brass feeler gauge. Anyway, put a feeler gauge in the gap and then push on the rotor shaft and see if the gap grows.

Without the feeler gauge in the gap, you may have trouble seeing if the gap grows. If the grows to the point that you can pass a .017 feeler gauge through it, the the distributor shaft bushing is worn out. At this point you would be best off just getting a reman distributor. If you have a lot of miles on this vehicle, your best bet maybe to go this route anyway as often all the little parts fail, and they are expensive and when the shaft bushing finally reaches its limit, you will have to buy one anyway, and all the money spent on the other parts will be waisted. Been there, done that.

“First, taking resistance readings of a coil is difficult at best as coils have a reactance to them. You have to wait until the current stabilizes to get a good reading and this can take some time.”

Not so. The DC resistance of a coil is easily and quickly measured by an ohmmeter. The DC resistance of a coil is an important specification as it can show whether the coil is open, directly shorted, or if there are low resistance paths within the coil. The important thing to do when measuring a coil, or any electrical device for that matter, is to make sure that it is disconnected first.