With help from many of the good folks who share knowledge in this forum, and proper maintenance, my family and I have enjoyed almost 14 years of delightful, worry-free driving in this car. Until a few weeks ago. My son and I decided to take it to run an errand on a Saturday morning, and as always, it started, idled and ran perfectly. One mile later, we were idling at a traffic light. On green, I touched the accelerator, and it stumbled and shut off. No spark. I ran through a diagnostic list I believe I found in the archives. The results pointed to a deceased Amplifier. I replaced the GM HEI module inside the Lucas AB14 box with a 5596 module from MSD. I did not disturb the condenser nor over-voltage diode. Still no spark. I ran through the checklist again. The results were very similar, and condemned the new module. Since a faulty new part is not unheard of, I ordered a replacement-replacement HEI module. I installed it and arrived at the same result, no spark and readings telling me that the amplifier is suspect. This time, though, I noticed that the coil got awfully hot to the touch while I was going through the tests with the ignition key in the on position and/or cranking. Since it was in its teens, and not the most expensive part to replace, I did so with a Lucas DLB 198. Still no spark, and you guessed it, fingers still point at the amplifier. I am embarrassed to report that rather than reach out to people who know a whole, whole lot more than me, I convinced myself that it might be the pick up base wreaking havoc. I ordered a new one, installed it and, yes, we are still without spark and the checklist still points to the amplifier. The only thing I noticed when cranking after installing the new pick up is that the tachometer jumped around a bit. Prior to that, it had not moved off zero. It has since gone back to not moving. The wiring all appears to be in good shape, but I have not checked continuity on anything to verify.
I am discouraged, but not ready to give up! If anybody can shed some light on what I have undoubtedly overlooked, I would be grateful for the assistance! Here are the current results with the second new HEI module, new pick up module and new coil:
The test assumes a fully charged battery 13.05V IGN OFF 12.20V IGN ON
Measure voltage at coil “+” terminal with key “on”. It should be within
one volt of battery voltage. If not suspect a problem with the wiring to the
ignition switch, or the switch itself. 11.24V
Measure voltage at the coil “-” terminal. Result should be the same as at
the “+” terminal. If Ok, go to step 3. If not… Not… It’s 3.84V
Disconnect the wire from the amplifier from the “-” post of the coil and
measure voltage again. Less than 2 volts means the coil is faulty. More than
2 volts means the amplifier is faulty. 12.95V
Disconnect distributor pickup coil from the amplifier (this is the
harness from the distributor that plugs into the amp). Measure resistance
across the terminals. It should be 2.2k to 4.8k ohms. If Ok, go to step 4.
If not, replace the pickup. 2.75K ohms - (The original unit measured 3.47K ohms resistance)
Reconnect the pickup to the amplifier. Measure voltage at coil “-” post
while cranking engine. The voltage should drop. If OK, go to step 5. If
not, the amplifier is faulty. Dropped from approximately 10V to 6V
Check distributor cap and wires, distributor rotor arm, spark plugs, coil
wire Everything appears to be proper. I replaced the cap and rotor after the second HEI module did not bring spark back. By the way, I bench tested the original GM module that was in the AB14 box and it failed. The first replacement bench-tested good, though.
Another observation is that with both of the amplifier leads disconnected, the coil ‘+’ and ‘-’ read the same voltage. Probably useless trivia, but perhaps worth mentioning.
As you’ve figured out by now, I know only enough to have a beautiful, disabled car in the garage with winter coming. Boy, would I like to drive it to storage! Thanks for taking the time to read my essay. I look forward to reading your insights.