long-time intermittent miss - SOLVED??

[dodger tom]

for years i've suffered with intermittent missing and hesitations in my '78 california champagne edition fi 2.0.

it would drive fine for miles and miles, and, for no apparent reason, begin missing and sporadically losing power. sometimes the missing/hesitation would last for a day or two, and sometimes it would only last for a few miles.

over the years i've replaced plugs and wires, distributor caps and rotors, vacuum hoses, s-boots, oil breather tower gaskets (and oil breather towers), fuel filters, fuel pumps, ts2's, and fuel-pressure regulators. i've installed a rebuilt amf, rebuilt throttle body, rebuilt distributor, and new fi harness. and, i've had the injectors cleaned. twice.

the problem with an intermittent miss is that it takes time before i can tell if anything works. up until two weeks ago nothing has.

for the past decade or so i've been running a pertronix ignitor ii. recently, i thought i might try out mechanical points and condenser to see if that made any difference.

before i did that, though, i figured i'd test the coil. i've always been told that coils either work or don't, so i'd never swapped my bosch blue for the original (spare) black bosch. but, as i often question things other people take for established truths, i thought, what the hell.

so, i whipped out my multimeter and pulled the coil. first i tested the spare black bosch, and got readings on both circuits within specs. when i tested the secondary circuit of the bosch blue (#1 & #4) i got a reading of around 3 ohms, which, i believe is about right.

when i tested the primary circuit (#1 & #15) i got no reading at all. so, that means no continuity, right? no circuit! so, the bus shouldn't run, right? except it did.

i figure there must be a small break in the primary windings, but the current arcs across that break most of the time, except when it doesn't, and then the bus misses/hesitates. does this seem like a plausible guess/explanation?

unfortunately, i never did the spark test so i don't know if the spark was nice and blue or weak and yellow.

anyway, i drove the bus a bit over 800 miles last week when i went fly-fishing near mammoth, ca. nary a miss/hesitation the whole trip. being a cautious soul i haven't declared victory yet, but i am hopeful.

this seems like a one-in-a-million kind o' thing, but i thought i'd share it just in case someone else has an intermittent miss/hesitation that they can't track down.
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1978 Champaign Edition 2 Westfalia
Would never find the time to keep up another classic air-cooled.

[SGKent]

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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[aeromech]

Thanks for your post
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[busdaddy]

Yeah!, what they said!^^^^
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[alaskadan]

Nice! Same problem on my 63 corviar spyder convertible. Intermittent oproblem over a couple years. After carb rebuild twice and turbo check on a dyno we finally threw a coil at it and problem solved. It just didn't seem like an electrical problem.

[richparker]

800 miles fly fishing and no trip report?

Nice find!
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’71 Westy build
Adventure thread
’65 Deluxe Build

[dodger tom]

[richparker]

That’s funny!

I use to do individual trip reports with my ‘68 Tin Top, The Bone Bus. After all those topics I decided to do just one adventure thread with Peryl. Unless I m doing a big trip to Cali, then I use the Cali thread I started back in 2014.
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’71 Westy build
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’65 Deluxe Build

[telford dorr]

[dodger tom]

[dogmeat]

is it an auto-ranging meter or do you have to select the scale? the wrong scale can give readings that are easy to misinterpret

telford hit the high points like12v won't jump a gap, and low ohm readings are tricky with standard meters

3k on a secondary winding sounds low. they are typically 6-8k area. I would expect at least 5k... I'd have to measure one, but 3 k sounds low and would indicate a short across some of the windings

[Abscate]

[jlrftype7]

dodger-tom- here are some more 'hilarious' Coil failings I've seen over the years.
Coil only acts up on Left turns, would not fail the ignition system on any right turn. Coil mounted horizontally on the inner fender. Bad Coil, new coil no longer cared which way you were turning .... Which is a nice thing to have...

Coil tests perfect in its stock upside down mounted position from Factory at the engine firewall. Upon removing the coil, with the test leads still hooked up to it, the winding showed its true nature and the readings started to jack knife all over the place. Bad Coil, but you would not have caught a bad reading in the stock position unless maybe you bumped the coil just right.
So, don't feel bad, Coils do some strange things at times...
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