Running okay last week. One week later, won't start. Turns over okay, but no spark. (No jolt at spark plug cap.) Wire looks okay, but the cylindrical (condenser?) on top of the head is peeling its varnish coating.

fuses good< oops
scan the PCM see errors cranking OMG it tells you why:? sure can.
forgot the 6 new spark wire plug set, replaced 1 by one never all at once, 6 new OEM type spark plugs and gaped correctly
22 year old spark parts are no good ever.
test for spark on all 6 yet, spark is 1st or there can be no FIRE.

4.3L cranks but will not start and run and stay running.(problem1)
fire cant be seen, but spark can.
1,2,3 engine,spark, fuel good 1,2,3 in that order
spark and fuel can not run a dead engine, so 1 is first engine'
compression good 150psi up not lower, all near same
next is spark if EFI sees spark
actual fuel pressure not told just OKay. pressures matter big time in EFI, and at cranking for sure. then idle and WOT later.
engine is free running so all tests are safe, cranking too.
the service manual covers all fuel checks cranked, balance test and leak down tests.

watch scotty
https://youtu.be/064Ilsz8Fzg

When using starter fluid, remove air induction to the throttle body and spray a 1 to 2 second burst directly down the TB and promptly start.

Also a flooded engine will not fire, even with starter fluid. Pull a plug and see if it's soaked with fuel. If the plug appears dry and there is spark and it won't fire on starter fluid directly down the TB, then most likely the spark is too weak. Inspect cap and rotor for erosion. Look for signs of carbon tracks on the cap and the coil.

Hi there check you are getting a spark from the cap to the plug.Do this by removing the cap and holding it very close to the top of the spark plug then try starting it.You should see a spark jump across.
If that seems ok take out the plug and either give a clean with some wire wool gently or replace it if it looks old or is old!
Hope this helps ;o)
Regards
Roy

have someone try to start the truck while you watch the distributer cap look for sparks cross fireing between wire ends cheek inside cap for cracks or corroded contacts.

Check the fuel injectors, with the key on one side of the two wire connector will have battery voltage, if none is present then check the ECM fuses in the underhood fuel box.

It could be a bad distributor cap, spark plug wire, or spark plug.

If your plug wire is in the front, check it. It may have come lose and is making sporatic contact with the end of the spark plug. My wife did the exact same thing last week. You may have to look in the plug wire cap at the connector.She bent ours so it was larger than it should have been and not "snapping" onto the plug when pushed on. I just lightly squeezed it together with a plier and then it snapped back on night and tight. Ran great after that.

it sounds like your crank positions sensor is going bad, take it out and clean it up and then see if it works, you might have to replace it but try to clean it first.

ok inot to familiar with vw however if its a diesel motor then it runs on glow plugs i would belive that , that would be the problem. (atleast with semi's) however if you do have spark plugs to check for spark pull the spark plug with that goes from the ignition pack to the distributer cap, (the distributer caps main feed in not out) have a friend start the car, let the wire hang in view and look to see if a spark emits if no spark comes then it could be the distributer. the rotor in the distributer cap, or a busted timming belt...Anoyther way to test for spark is to pull a plug from the head, re-connect it to the spark plug wire that it was connected to, take a screw driver or something , wait a butter knife is the best tool actually, put it on the end of the spark plugs head, rest the butter knife on top of the alternator or anywher you can geta good ground(non-painted surfaces) and hold the the spark plug wire on the rubber part pushing the head of the plug on the butter knife which is on a good ground and turn the car over, just a couple times not really trying to start the car just a couple revolutions and look for a spark..if no spark is seen then the above problems are true for this problem......If you are getting spark, then you need to check your fuel pressurecontroll modulator , i believe its called, its the last gateway b4 fuel is disspursed through the injectors...let me know if this was helpfull.

Try checking the spark plug, and the spark wires, if that doesnt clear things up then try replacing the roter under the distributor cap and check the cap for any corrosen