Now it can be told. I was supposed to be at last week’s Carlisle Import car show with my car. I had planned for this, and had looked forward to it for months. I had driven the car numerous times this season without issue. But it didn’t happen, and here is why.

Friday morning the 15^th of May, at 7 a.m., I ventured into the garage, got into the car, pulled out the choke and hand throttle as always when making a cold start, and the car immediately fired up. I inched it out of the garage and sat in the car for a few moments while the engine slowly warmed, playing with the hand throttle to find just the right idle. (My dual Weber-carburetor-equipped 1.3L engine has always had a slightly fluctuating idle. The late, great Alfa guru, Pat Braden, has written several technical books which I own. He always preached: “If the car runs fine, don’t mess with the carbs!” So I haven’t. My car runs very fine, it runs excellently in fact, so I’ve tolerated an idle that can vary between 800 and 1200 RPM.)

I prefer to see the water temp gauge move at least partway toward its middle mark before driving the car, so, with the engine idling a little higher than 1200, I applied the parking brake and went inside to check on my wife, who was still enjoying her first cup of tea for the day. I was in the house for about 15 minutes and decided to head back out. As I got near the car, I realized that the engine was not running; the car had stalled, and the ignition remained on. I tried not to panic, but knowing that it’s not the best thing to leave the ignition on when the engine is not running, I quickly jumped into the car, turned the key off, and tried to start it again. With a healthy battery providing plenty of cranking power, the engine turned over without an issue, but made no attempt to fire. Now it was time to panic.

I didn’t know what to check first. I grabbed a spare coil I had and without removing the installed coil, switched over all the wires. No difference. I removed the distributor (a one-minute job) and hastily replaced the points and condenser with a new set. No difference. My wife sat in the car and cranked while I held the number one spark plug wire close to the valve cover, checking for spark. Nothing. After 45 minutes of this, we pushed the Alfa back into the garage, climbed into the Volvo XC40, and drove to the diner where I was scheduled to meet with two other club members so that we could caravan to the show. To say that I was bummed is an understatement.

Thankfully, the camaraderie of my fellow AROC NJ members cheered me up. I enjoyed Friday’s show, and we headed to our hotel to check in and relax before dinner. But I couldn’t relax. I spent an hour on my phone researching automotive 12V ignition systems. Was it the coil? The points? The condenser? Any of these could have overheated with the ignition on. But I had tried replacement parts for all three, without success. Perhaps in my haste I did something incorrectly.

Saturday’s show was even better than Friday’s, and as I headed home, I felt confident that under less stressful conditions, I could figure this out. I was too bushed on Saturday to tackle anything, but on the following afternoon, I took my sweet time as I installed a known good used coil, and pulled the distributor once again. Talk about a rush job! The point gap from Friday’s “repair” was about four times as large as spec. I doubt that the two halves of the points were even touching! I fixed that, and for good measure, threw in a new set of plugs, which the car was due for anyway.

After about two hours of work, it was time to try again. Somewhat nervously, I climbed in, inserted the key, pumped the gas, turned the switch to “crank”… and the engine started right up. WHEW!

So what was it? I don’t exactly know, and that doesn’t worry me, as long as it’s fixed. Something overheated, and it’s a good guess that it was one of the three items I replaced. Lesson learned: don’t walk away from my Alfa at idle for more than a few moments.

 

TESTING AN IGNITION COIL

As a healthy side-effect of last week’s failure, I investigated how to test an ignition coil, something I’ve never done. During my entire automotive career, I have never seen a coil fail, although colleagues have told me that they have. An internet search quickly taught me that a DMM (digital multimeter) can test for resistance, both at the primary and secondary windings.

 

This is a brand new Bosch “blue” coil, a very popular installation for classic European cars. I bought mine from my usual supplier, Classic Alfa in the UK, for $72.

 

The top of the coil has three places for connections to be made. On the left and right are the primary wiring connectors, for 12 volts of power. The plus symbol on the right indicates the positive connection (also marked “15”), and the minus symbol on the left indicates the negative connection (also marked “1”). In the center, marked “4”, is the secondary wiring which will feed high voltage (20,000 to 30,000 volts) to the distributor and spark plugs.

 

This is my DMM, which can test for AC voltage, DC voltage, amps, resistance, continuity, and dwell. I want to test for ohms, or resistance, so I will be using the scale on the right. I’ve drawn a bright green circle around the infinity symbol, indicating resistance. My first check will be in a very low range, so I will be using the ‘200’ range, which has  red circle around it. The two probes are connected to the DMM and are indicated by the blue arrows. The red probe, for positive, is connected where the infinity symbol is. The black probe, for negative, is connected at “COM”, for “common”.

 

To test the primary windings, the positive and negative probes are connected to the positive and negative connections on the coil. In this case, either probe can go to either connection. With the DMM’s scale set to 2oo, our result is 2.9 ohms. Spec for this coil, depending on which website I read, is between 3.0 and 3.4 ohms, so I’m not concerned about this reading, as my machine may be slightly inaccurate. An important point: this result indicates that there is an internal ballast resistor in the coil, so an external ballast resistor is not needed! A reading closer to 1.0 to 1.5 ohms would indicate lack of an internal resistor, requiring installation of an external one.

When testing the secondary windings, I am expecting a result closer to 7,000 to 8,000 ohms, so I have changed the scale to “20k’, indicating 20,000. One DMM probe is moved to the center, secondary, coil connection. The screen shows 6.41, which is read as 6,410 ohms. Again, this is a little lower than what I’ve found on the internet, and this could be attributed to my DMM.

Even if I never have the need to test a coil again, this was a useful exercise, and helped remind me to focus on the basics first when performing automotive repairs.

 

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