Mysterious Ignition issues

[sipndiesel]

1982 Rabbit, 4 door, black tie edition, 1.7 Gas, 160k miles.

The previous owner warned me of this mystery ignition failure. When driving down the road, the car will just shut off, as if you turned off the ignition with the key. No warning, no sputtering, just shuts off. Then after a time..usually 30 min or so, the car will re-start and drive as if nothing has happened. I have checked the coil, the resistance on the primary and secondary is within specification, I have even replaced the ignition switch. The previous owner verified the ignition module was well grounded (by soldering a ground directly to the battery lead)...so I don't think there is a problem with grounding for the ignition module

My next plan is to replace the coil and ignition module, but I hate to do that only to find that something else was the issue. Could it be the coil wire and is there a way to check it for failure under load or possible heat issues (which might explain why it will start up after a period of time)

Any help would be greatly appreciated..

[TDCTDI]

Check ignition rotor & distributor cap, cheap aftermarket ones can cause weirdness. Check grounds, especially at valve cover , as gasket shrinks ground will loosen. Ground connection between engine mount & transmission can sometimes get corroded. Fusible links in harness under battery. Ignition switch & power relay also possible.
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[crsmp5]

if you add a jumper wire from batt to coil.. does it run? you do this once it dies..

after you know that then you will know if electrical issue or component..

now to remove coil wire from cap, point to head.. if it does not restart... pull 3 wire plug off dizzy, ground middle wire and each time its grounded will/should make spark... does it?

if yes.. and with 3 wire plug connected, pick up in sizzy bad... if no.. the little black box needs replaced with a known good one.. repeate test.. if still no.. its in the harness.. between dizzy and black box..

now if jumper wire from batt to coil resolves issue.. remove jumper.. pull hignbeam lever on and as holdhimg it on.. will it run?? if yes.. reply... if no.. id change ignition switch/look at the power curcuit not melted in the electrical boxes under dash...

if it does run.. where i asked for reply.. between batt and inner fender the harness needs opened up.. follow the power wire from batt to where the wire is PINCH WELDED to other power wires.. its green from corrosion/faling.. BUT you cannot just butt connect the wires.. they do not make one that big.. copper tube, and a huge pair of cable crimping wires does build a nice butt connector though
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[ps2375]

Sounds like a fuel pump. When the pump stops, so does the motor, right away. Toss a timing light in the car and when it dies, check for spark. No spark, ign system: has spark, fuel system. Could also be the relay, but those generally heat up and fail and burn contacts and never work right again.

I guess I should ask, CIS or carb? My answer applies to CIS.

[sipndiesel]

Ok...I was able to check the ignition module last night according to the Bentley procedure...chapter 5, section 4.2. When I checked the voltage across the coil with the ignition on (not actively trying to start the engine) I get a constant 2.2V with no drop in voltage...according to the manual, the voltage should indicate a minimum of 2 volts for 2-3 seconds then drop to zero volts. So, it appears I have a failure in the ICM... I also tried the same test with someone actively trying to start the motor and found the same 2.2V constant across the coil during the starting effort with no drop in voltage.

I just wanted to make sure this failure is typical before I go drop $75-100 on a new ICM...only to find that it was the coil..or should I purchase both together?

Looking for some confirmation on the testing procedure (and my perceived failure of the ICM) most of all...

[ps2375]

It is possible for the ICM to fail, I have never seen one fail. I would try to find one at a salvage yard before buying a new one.