Why the heck won't you start?

We had auto shop in high school. Everyone that owned a car took it. I didn't own one, but being somewhat mechanical, I took it anyway. Our shop teacher would let you do work on your car and he'd grade you.

One time my buddy with an Alpha Romeo Sprint wanted to replace his brake pads. He only had time to do two wheels during class. Later on that night, him and I were cruising down some street and he was so happy that he had brakes, he slammed on  the brakes to show me. We immediately did a 180 and slid sideways between two parked cars and hit the curb. We got lucky we didn't hit anything but the curb. Apparently he did two wheels on one side of the car. He wasn't the brightest, but he was lucky. I remember more of what happened in this class than any other class. Art was second.

Those were the days.

@Stan Galat - My Grandfather had a big ol' farm house that had a "Summer Kitchen" - That was a big addition off the side of the house, all by itself, with big windows on two sides to let the breezes through and cool the kitchen from the wood-burning kitchen stove.  Under that kitchen we could store the 12 cords of wood needed to heat the house in the winter (I'm not making this up) and off to the side down there was the outhouse.  It was a 3-holer.   I never quite figured that out, the three holer part, but it came in handy when the power went out during storms and the water pump didn't work and the toilet wouldn't flush.  

I got my first pair of shoes as a teen and walked backwards in the dirt for a couple of weeks just to see my new, strange looking footprints !..................Bruce

Shot myself in the foot, again. In the first post in this thread I talked about being suspicious that the battery cutoff switch was the cause of the starting problem. It turned out to be a few bad diodes in the EMPI alternator, but I removed the cutoff switch prior to finding that out.

Recently, I totally rewired the ECU and engine compartment. In the process of doing electrical work, I added a battery switch back in. In an abundance of caution, I used an 80 amp circuit breaker instead of the old switch.

Since that rewire, I've had the breaker pop on at least 3 occasions. I finally figured out that it only did it when the engine was totally warmed up and I was restarting the car. Aha, 80 amps was borderline when the oil cooler fan was on and I was starting the car.

I got a killer deal on 3 - 100 amp breakers and replaced the undersized one. So far so good. My foot is feeling better until the next unplanned event.

If someone needs a 100 amp breaker and wants it for the cost of postage let me know. I'll keep one as a spare.

EMPI failure..Im seeing a trend here

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'Battery cutoff switch' and 'blown alternator diodes' in the same sentence rang a bell in the increasingly fuzzy recesses of my head. So, I've done some googling and found this on a British car forum (where else?).

Basically, using a cutoff switch to stop a running engine is nonsense up with which alternator diodes will not put.

Of course, you knew that and would never do that, but, you know, sometimes we get forgetful in our dotage.

If it matters, or is at all relevant, I've never managed to blow out diodes on an alternator. Too sheltered a life, probably.

"The regulator's job is to maintain about 13.5V at your battery +. If your alternator is turning disconnected from the battery, the regulator "sees" nothing, which is equivalent for him to Ov. So it gives more field to the rotor, to increase the output voltage which goes to the rectifier diodes. Voltage can go up to 80ish V, enough to "burn" the diodes. If you use a master switch without a resistor (or uncorrectly wired resistor), that's what happens if you cut your engine with the switch, especially at high revs (emergency, ...) On well built switches, the resistor is between the output and the earth. Low resistance -> high current -> low voltage -> safe diodes. Jeff LHD 1990 BDR"

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@Sacto Mitch posted:

.Basically, using a cutoff switch to stop a running engine is nonsense up with which alternator diodes will not put.

Of course, you knew that and would never do that, but, you know, sometimes we get forgetful in our dotage.

"The regulator's job is to maintain about 13.5V at your battery +. If your alternator is turning disconnected from the battery, the regulator "sees" nothing, which is equivalent for him to Ov. So it gives more field to the rotor, to increase the output voltage which goes to the rectifier diodes. Voltage can go up to 80ish V, enough to "burn" the diodes. If you use a master switch without a resistor (or uncorrectly wired resistor), that's what happens if you cut your engine with the switch, especially at high revs (emergency, ...) On well built switches, the resistor is between the output and the earth. Low resistance -> high current -> low voltage -> safe diodes. Jeff LHD 1990 BDR"

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Great point, Mitch. I haven't tried that trick (removing the battery from the circuit) since the days of mechanical regulators. It worked fine then, but I can see that some cars might go unregulated if the battery is disconnected.

Remember, I haven't done that, and don't plan to. However, would it really work that way for a type 1? Say the engine is running and the alternator is charging the battery at 13.5V. If you disconnect a battery terminal, the charging light, regulator and alternator are still in place in the circuit, there's just a little less load on the alternator (and the regulator will keep the voltage at 13.5V to reflect the lower load).

It seems to me that to make the regulator runaway, you'd have to remove the feedback from the alternator output to the regulator. At least on my car, that's no where near the battery terminals.

Thoughts? @DannyP?

It is certainly possible that a hinky/defective switch could cause a voltage spike that would turn an alternator's diodes to burnt toast in a millisecond.

I recommend keeping the battery in the circuit at all times. LOL!

I don't use one of those battery disconnect switches. I do have a thumbwheel battery cable though, so I can disconnect quickly when working on the electrics. It is secured with a ty-rap, I drilled a few holes in the wheel so I can secure it wherever it's tight.

Thanks, Danny. That's the way I use my breaker now (just when I'm working on electrics). I decided on a breaker rather than a switch to avoid blazecut temptation. :-)

I use my switch when I am working on the car and as extra security sometimes when I park it.

Circa February 1992 I drove from Hartford Connecticut to Concord New Hampshire in my 1980 Honda Accord in order to cover the Presidential Primary the right way, in person, with an experienced photographer. On Day 2 of this field trip Theresa, our comely intern joined us in her jalopy, and we all had an enjoyable several days galavanting around the Granite State through the slush with the likes of Pat Buchanan, Bill Clinton, Paul Tsongas and . . . Tom Laughlan, erstwhile star of the "Billy Jack" movies.

On the way home Theresa's car would not start after a gas stop. Chivalrously, and with my car running, I carefully removed my battery and placed it in her car's battery box, replacing hers with mine and mine with hers. We all drove home without incident.

Just putting that out there.

@edsnova, Thanks, somehow replacing the battery was a twist to the comely intern story that I did not anticipate. In my case, I replaced the battery already and to the best of my recollection, I did not have... (wait, that was Bill Clinton).

I replaced the 80 amp battery breaker with the 100 amp breaker. So far, no repeat problems.

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@edsnova posted:

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...Chivalrously, and with my car running, I carefully removed my battery and placed it in her car's battery box, replacing hers with mine and mine with hers...

If Ed were to try that today, he'd probably fry half the computer chips in a modern car.

I wonder how much an overabundance of technology has led to the death of chivalry in this century.

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