Spontaneous Engine Cutout - Diagnosis

[sped372]

A successful diagnosis of an unannounced engine death in the Ghia, in case it helps someone in the future:

Yesterday the wife and I backed out of the driveway and headed to work. About a block from the house the car died without warning. Wife was driving and since it happened so quickly she couldn't remember whether it died in gear as she was about to shift from first to second, or after she had already pushed the clutch in. Regardless, it wouldn't restart. Cranked over strong but no coughing. After a few more cranks I had her pop the decklid and I looked for any obvious disconnected wires at the coil, etc. I could hear the cutoff solenoid clicking so I knew there was electricity back there. Assuming it may have been flooded by that point (could smell fuel) we left it parked on the street, walked home and took the other car to work.

After work the car just cranked and cranked again, no coughing. I assumed something electrical based on the instantaneous and complete failure to run.

Diagnosis Steps:

1. Voltage at battery (somewhat redundant based on good, strong cranking): 12+
Battery seems fine

2. Key on, voltage at positive side of ignition coil: 12+
Ignition switch and wiring from battery to coil is fine

3. Key on, voltage at cutoff solenoid and choke: 12+
Wiring between coil and these items is fine

4. Car in neutral, parking brake set
5. Key on, voltmeter connected between ground and negative side of coil, rotate engine by hand: no change in voltage
Suspect points

6. Remove distributor cap, observe points while rotating engine: they appear to open and close
Was expecting to find something more obvious

7. Key off, voltmeter set to measure resistance while still connected between negative side of coil and ground
8. Rotate engine by hand: no change in resistance (always infinite)
Points are not functionally opening and closing

9. Check point gap: seems right, but observe resistance drop to zero with feeler gage bridging the point gap
Points are functionally always open

10. Remove points for inspection: observe a pretty severe pit cap-and-cone
Most likely leading to imprecise gapping

11. Replace points with spare, regap, replace distributor cap: engine fires on first turn of the key

12. Retime engine

Glad it turned out to be something simple, as I suspected it was.

[Amskeptic]

Glad it turned out to be something simple, as I suspected it was.

This is the classic closed points behavior. Like many other things threatening the survival of the human species, there is a hockey stick graph of increasing discontent, that is all but over when the symptoms become noticeable. In the case of the points, as the gap closes down there is a "residual" spark that can easily bridge a small gap no matter what the condensor valiently tries to prevent, leading to surface oxidation.
Colin
(you never forget to check the points once you have been bitten, and .016" gap just doesn't look that different from a .006" gap when you are doing a visual-only)

[sped372]

Weird thing is, it was "always open" points, not closed. I had checked the dwell not long ago at tuneup time.

[RSorak 71Westy]

Modern day points sets are crap.....Get a pertronix and be done with it.

[Amskeptic]

Modern day points sets are crap.....Get a pertronix and be done with it.

My Pertronix melted down in Los Alamos with poisonous clouds of PCBs just because I was driving.

The BobD spare original points in the glovebox saved the day. Haven't touched them for 12,000 miles so far.
The Squareback has its points from when I bought the car in 2006, 23,000 miles on them since gapping.
Chloe is at 2,000 miles since I last gapped them.

I will be crying besottedly in my beer when I have to buy new points.
Colin

[RSorak 71Westy]

Yes Pertronix's are not perfect But I've never had one fail on over 15 years of personal use on 3 vehicles I own. All the vehicles run much better than they ever did with points.

And yes thats one of the great advantages of a pertronix its designed so that you can switch back to stock in minutes if need be.

[bigbore]

I have a few of those pertronix crap out on customers cars I can't tell the difference when driving a vw with or without one the points run just the same. Here all my vw fleet are still on points and will stay they way. They require little maintenance trouble free for many a mile.

[ruckman101]

After I cooked my pertronix, I went back to points. Cheaper to replace. My coil failed shortly after installing the pertronix, too.


neal

[vdubyah73]

compufire on buggy for 8 yrs, on the bus for 6. no problem ever. if on a long road trip, i pull the whole dizzy out of the buggy and take it with me.... just in case. ;-)