EP Question about Coil test

A quick follow-up on yesterday

A quick follow-up on yesterday's discussion. (Pertronix installed as per your guidance yesterday). Tested the coil--here's the results:

I get nearly Zero Ohms (about .2 Ohms) on the Primary side. Red lead to (+) and Black lead to (-) with all leads detached--just a bare coil.

I get 10 Ohms on the Secondary side (All leads detached. Red lead to + on coil and Black lead to center).

I double checked with my spare coil. Got about 9.5 Ohms on the Secondary and zero ohms on the Primary side.

What's going on? I thought I needed around 3+ Ohms on the primary side to make the Pertronix work?

"3+ ohms is the resistance

"3+ ohms is the resistance of the windings which is the resistance between the + and - terminals not the + and the lead wire as you are measuring. You are measuring the "tap" point where the high voltage is generated. Or maybe I'm misunderstanding what you are doing but unless the coil is shorted, or it is an accel or MSD high performance coil with extremely low impedence then it should be above 1.5 ohms."

"Jamie,

The coil I'm te

"Jamie,

The coil I'm testing is a stock Bosch Coil from an AQ 140A. My backup coil is off an AQ125A. Both test about the same.

I measured the Primary Circuit (+ and - on the coil) and got nearly zero Ohms every time. Tested as noted in my first post.

I measured the Secondary Circuit (the high voltage side) and get around 10 Ohms."

"Well if both are testing the

"Well if both are testing the same then there is either something wrong with both coils (the windings are shorted) or your multimeter is off calibration. I would say that your multi-meter is probably out.

Touch the leads of your multi-meter, if the reading is zero, then you have a problem. It should be .3 ohms or something from internal resistance. this will mean that your multi-meter is not calibrated and not reading low resistances correctly."

"If not mistaken, those coils

"If not mistaken, those coils have the same specs, (Aq125 and AQ 140).
However calibrate Your multimeter:
Out both cables together - adjust to 0 ohms, or subtract reading from the measurements of the coils."

"Jamie and Morten, I've ca

"Jamie and Morten, I've calibrated the multimeter. It's just a small inexpensive analog type but seems to do the job. The needle sits right on Zero.
I found another coil in my shop that came off a running AQ 125A. All three coils test nearly identical. Very close to 10 Ohms on the Secondary circuit (high voltage) and zero or very close to it on the Primary circuit.

The strange thing is that the meter is reading the 10 ohms (+ or - maybe 1/4 ohm) on all coils but nada on the primary circuit on all three. Maybe time to upgrade my multimeter?

Here's the next question. Assuming these coils are good. Do these Bosch coils have the 3 Ohm resistance (from the factory) that I need to run the Pertronix properly?"

"Dennis, try with a digital mu

"Dennis, try with a digital multimeter. I would not rely on a cheap analog meter to measure a small resistance, and the readings you are posting do not make much sense to me.

I don't remember what the original coils' reading should be. However, I can tell you that 3 ohm coils work with Pertronix kits for 4 cylinder engines, but 1.5 ohm coils do not."

"E.P.,

Yes, it has to be a

"E.P.,

Yes, it has to be a problem with my cheap multimeter. I'm getting the same readings for 3 different coils from VP 4 cyl. motors.

Time to pick up a decent digital meter."

"That was what I was saying ea

"That was what I was saying earlier dennis. If you touch the two multi-meter leads and it is zero then it is probably a problem where it is not accurate enough to measure small resistances. Lets say the tolerances are +/- 3 Ohms and you are trying to measure 3 Ohms...

On a side note I believe the new Pertronix and Hot spark modules do work with 1.5 Ohm coils but double check on that. I think they have upgraded all the units to higher more current. I know for a fact Hot Spark has and I believe Pertronix has too. I am running a 1.5 Ohm Bosch coil with Hot Spark."

Pertronix can and does handle

Pertronix can and does handle 1.5 ohm coils as long as it is for 8 cylinder applications. Unless they have changed their specs they were quite adamant that a 3 ohm coil is to be used for 4 cylinder applications.

"Got my new Digital Multimeter

"Got my new Digital Multimeter today. Retested the coil. SUCCESS!
Primary: 3.5 Ohms
Secondary: 9.37 Ohms

Thanks to all of you for furthering my education! I can build a house but I couldn't test a coil properly! "