Soly
You could follow the steps Bill Buttermore outlined above.

Took the #6 wire ( I had marked them at the coils with a silver marker) stuck the multimeter probes in and twisted, tugged, and downright pulled on the cable, actually pretty hard. The resistance reading, about 7.3 kohms this morning, never once dropped off to indicate a broken conductor. Maybe it was the insulation that broke down and it was arcing against the engine cover bracket. The "suspicious" marks I had seen were white, not black. Or maybe the conductor will read resistance OK but not conduct 50,000 volts consistently.

So maybe I would have seen a light show if I had a little spray bottle and some darkness instead of foolishly working in sunlight. I suppose I could swap out the old #6 wire for one of the new good ones......wait - nope, I ain't pulling off those new boots. No way.

I had purchased the Beldens at NAPA two years ago, don't have the receipt, and figure it was me who broke the conductor, even if I was careful. All the same, the receipt for the new "lifetime" (ha-ha) wires is in the glovebox.

Here'* a question. How does the PCM isolate and record a misfire?

Here'* a long read that may help with that. It'* for the 2000 - but perhaps yours would be similar.



P0300

CIRCUIT DESCRIPTION

The Powertrain Control Module (PCM) has the ability to detect a misfire by monitoring the 3X reference and camshaft position input signals from the ignition control module. The PCM monitors crankshaft speed variations (reference period differences) to determine if a misfire is occurring. If 2 percent or more of all cylinder firing events are misfires, emission levels may exceed mandated standards. The PCM determines misfire level based on the number of misfire events monitored during a 200 engine revolution test sample. The PCM continuously tracks 16 consecutive 200 revolution test samples. If 11 or more misfires are detected during any 10 of the 16 samples, DTC P0300 will set. If the misfire is large enough to cause possible 3-way catalytic converter damage, DTC P0300 may set during the first 200 revolution sample in which the misfire was detected. In the case of a catalyst damaging misfire, the MIL will flash to alert the vehicle operator of the potential of catalyst damage.

CONDITIONS FOR RUNNING THE DTC

* None of the following DTCs are set:
* Vehicle Speed Sensor (VSS) .
* Throttle Position (TP) sensor
* Engine Coolant Temperature (ECT) sensor
* Crankshaft Position (CKP) sensor
* Camshaft Position (CMP) sensor
* Manifold Absolute Pressure (MAP) sensor
* Mass Air Flow (MAF) sensor
* The engine speed is between 550 and 5800 RPM .
* The system voltage is between 9 and 18 volts .
* The ECT indicates an engine temperature between -6°C (20°F) and 120°C (248°F) .

CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft RPM variation indicating a misfire sufficient to cause 3-way catalytic converter damage or emissions levels to exceed mandated standards.

ACTION TAKEN WHEN THE DTC SETS

* The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic has been run and failed unless three way converter damage is possible in which case the light will illuminate after the first failure.
* If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control, and the EBTCM will illuminate the TRACTION OFF lamp.
* The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC

* The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
* The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
* The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
The scan tool provides information that can be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as DTC status Failed Since Code Clear, the misfire history counters (Misfire History Cyl #1-#6) will still contain a value that represents the level of misfire detected on each cylinder. The scan tool displayed misfire counter values (Misfire History Cyl. #1 through #6) can be useful in determining whether the misfire affects a single cylinder, a cylinder pair (cylinders that share an ignition coil - 1/4, 2/5, 3/6), or is random. If the largest amount of activity is isolated to a cylinder pair, check for the following conditions:

A misfire DTC may set if components that affect the crankshaft position sensor have been recently replaced, and the CKP System Variation Learn Procedure has not been performed. If the diagnostic table does not identify a problem then perform the CKP System Variation Learn Procedure.

If the misfire is random, check for the following conditions:

* Crankshaft Position System Variation Refer to CKP System Variation Learn Procedure. The crankshaft position system variation compensating values are stored in the PCM non-volatile memory after a learn procedure has been performed. If the actual crankshaft position variation does not match the crankshaft position system variation compensating values stored in the PCM, DTC P0300 may set. The crankshaft position system variation learn procedure is required when any of the following service procedures have been performed:
* The PCM has been replaced.
* DTC P1336 has set.
* The engine has been replaced.
* The crankshaft has been replaced.
* The harmonic balancer has been replaced.
* The crankshaft position sensor has been replaced.
* Any engine repairs which disturb the crankshaft/harmonic balancer to crankshaft position sensor relationship.
* Check the secondary wires associated with the affected cylinder pair for disconnected ignition wires or for excessive resistance. If any spark plug wire resistance is more than the specified value, replace the affected spark plug wires.

Spark Plug Wires Resistance
3280-4921 ohms per meter (1000-1500 ohms per foot)

* A damaged or malfunctioning ignition coil. Check for cracks, carbon tracking, or other damage. Also check the coil secondary resistance. The secondary resistance should be within the specified range. Ignition Coils Secondary Resistance

5000-8000 ohms .

* Switch ignition coils and retest. If the misfire follows the coil, replace the ignition coil.
* Check the system grounds. Ensure all the connections are clean and properly tightened.
* A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the Failure Records conditions. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor.
* If the PCM stops receiving data from the EBCM/EBTCM, DTC P0300 can set due to a loss of rough road data. Check for stored ABS/TCS DTCs, especially DTCs related to a serial data malfunction. Refer to A

Diagnostic System Check - ABS in Antilock Brake System.

* Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for disconnected or damaged vacuum hoses, an incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces.
* Perform a fuel system pressure test. See: Component Tests and General Diagnostics\Fuel System Pressure Test A malfunctioning fuel pump, plugged fuel filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test. See: Component Tests and General Diagnostics\Fuel System Pressure Test
* Check the fuel injectors. Refer to Fuel Injector Call Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) or to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F) . See: Component Tests and General Diagnostics\Fuel Injector Coil Test\ECT Between 10-35 Degrees C (50-95 Degrees F) See: Component Tests and General Diagnostics\Fuel Injector Coil Test\ECT Outside 10-35 Degrees C (50-95 Degrees F)
* Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis. See: Component Tests and General Diagnostics\Alcohol/Contaminants-in-Fuel Diagnosis
* Check the EGR system for a leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.
* Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures less than 80°C (176°F), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 gm/* .

IMPORTANT: If the level of misfire was sufficient to cause possible catalyst damage (if the MIL was flashing), ensure that the DTC P0420 test is completed and passed after verifying the misfire repair.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Basics are it knows which cylinders are firing when the knock is detected.

Wow, Dick. That is a lot of good information. I wondered how the PCM could determine which cylinder was missing without the aid of the knock sensors (which on my car are now serving as fancy block drain plugs.) I did swap the 3/6 and the 1/4 coil to see if the miss followed the coil. It did not. And look at that recommended resistance. The #6 wire is about a meter long. So it shouldn't offer more than 4900 ohms resistance. Yesterday, when it was pretty hot from the engine, it was about 6500, and this morning when cold, measured 7300. That is out of spec. Maybe that'* all there was to it. Too much resistance.

Is this info from your Alldata subscription? Maybe I'd better have another look at that

Yes, it was from the AllData Subscription. I've found it useful for quick information, and it'* easier to navigate than the GM SPO program and the FSM.

you can use those metal boot covers from your stock wires on your new wires..

If you have them.