engine and drivetrain Car wont start. Coil fried?

[Chamoix]

I'll start with the basics and the question. 73 non-tii manual with Petronix and Blue coil that has been in the car since I got it 11 years ago. New distributor cap and rotor. Has gas at the carb (Weber 32/36), but no spark. Coil wire to the distributor cap when cranking reads battery voltage only. Is it fried?

Now the sordid details. I started a front subframe transplant about a month ago. Early on I was fooling around trying to see how the Harbor Freight engine support bar would fit and dropped one of the chains down the drivers side of the engine. There was a massive short. Smoke, sparks, etc. It took me a couple of seconds to find something to pull the chain out, by which time it was very hot and the oil sludge on the engine was smoking pretty good. Everything settled down and I promptly pulled the battery and continued on. Fast forward 4 or 5 weeks and things are back together far enough that I thought I'd crank the engine but it would not start. Wouldn't even cough with a shot of starter fluid and the electrical situation described above presented. The constant 12.5 volt reading on the coil to distributor wire when cranking makes me suspect the massive short may have fried the coil, but I have no experience here and thought I seek learned opinions. Thanks.

[adawil2002]

Could have killed the Pertronix, or a number of other things. Time to start checking continuity of the ignition circuit.

Put in points and condenser and coil are inexpensive, I'd start there.

[Simeon]

Would definitely look at the Pertronix first. The electronics are pretty sensitive. Coils are old skool and generally a lot tougher. I would be worried about your alternator as well

Put a dwell meter across the coil and crank over. If you get 0 degrees or 90 degrees then it is definitely toast

[02for2]

Easy enough to check the Coil using a DMM by measuring the resistance values.

Set DMM to ohmmeter function and test Primary Winding by placing test probes to each of the terminals on the coil (+/-). You want to see values between 0.4Ω - 0.6Ω.

Now check Secondary Winding by placing test probes on the + terminal and the Center terminal. Look for values between 5.0kΩ - 7.2kΩ.

If you get these values, coil is most likely good. If not, coil is definitely bad.

You could get these values and still have a faulty coil, but this would be due to internal shorting which would not become apparent until the coil reached (exceeded) normal operating temperature in which case, the engine would falter/stop. Check Coil temperature after fully warmed up - s/b warm to the touch but not HOT. But, this failure would not affect a cold start.

Cheers!

[Chamoix]

Using my Craftsman DMM set to the 200ohm range, I get 3.8 on the Primary. Set to the 200Kohm range I get 8.4 on the secondary. Sounds way off from what you indicated. That and the fact that I get a constant 12.5 volts on the wire from the coil to the distributor when cranking says I'll need to speak with Steve at Blunt in the morning.

Thanks for taking the time to assist.

Jim Daniels

jdaniels@uga.edu

[jimk]

3.8 ohms primary is perfetly normal. Read your Pertronix installation sheet, it says to have no less than 3 ohms primary.

[Chamoix]

Sometimes you get lucky. I went to pull the Petronix negative lead from the coil and just a stub with no copper showing slipped out of the connector with no resistance. I put a new connector on, slipped it back on the coil and it started right up! May talk to Blunt anyway and get a back up coil for the shelf.

[Chamoix]

Sometimes you get lucky. I went to pull the Petronix negative lead from the coil and just a stub with no copper showing slipped out of the connector with no resistance. I put a new connector on, slipped it back on the coil and it started right up! May talk to Blunt anyway and get a back up coil for the shelf.

[02for2]

Good Catch !!

I was talking about the Bosch Black Coil alone (admittedly an assumption on my part), with no consideration for Ballast resistance or another Bosch Coil such as Blue (built-in resistance) or Red.

Cheers!

[Napes]

FWIW the mechanic who worked on my car until his health forced his retirement about 5 yrs ago began working at the Tucson BMW dealership in 1970. When one of the other mechanics left a couple years later to open his own BMW shop he followed him and worked there for about 4-5 yrs. He then left and opened his own BMW shop where he worked, mostly single-handed, until his retirement in 2007.

He told me that in all those years, and all the '02s he'd worked on, he never had seen a coil on one go bad. Not that it couldn't happen, not that it hasn't happened, just that it's so rare he'd never experienced it.

Bob Napier

[02for2]

@Napes...

I totally believe that ! A Coil is a fairly simple and robust thing, and generally the last thing you suspect.

But believe it or not, I have come across two cars in our local group in the past 6 mos. where, after exhausting every other possibility, it turned out to be bad Coils. Swapped the Coils out and these cars have run trouble-free since.

So, you never know with these 40 y.o. cars.

Cheers!