Is your stock ignition system the Duraspark or Prestolite? I think in 78 they went to the Duraspark (silver/aluminum box mounted on the P-Side fenderwell). If I was you, with the engine running I would start wiggling the wires around the ignition module and see if you can get it to die. If it doesn't die, start wiggling the wires going to the coil. Since you said it would die when you slam the hood I would tend to believe its an issue with the ground to the ignition module on the fender well. If I remember correctly, if the Duraspark or Prestolite ignition module loses it's ground the engine will die... This really sounds like a bad ground to me but to prove the loss of voltage to the coil theory, you could always run a temporary hot wire directly to the 12VDC side of the coil and see if dies while driving. Hope this helps..
I have had this same problem back in the 1980s excluding the hood drop. I changed out the ignition module and it ran fine forever after.
I ran out of things to check and had limited knowledge to proceed but was sure happy the day the rig did not quit running going down the highway.
Last edited by RedNeckCorvette; 07-25-2015 at 04:35 PM..
Reason: poor suggestion - removed it after reasoning with it for a wile
I think he is trying to tell you to hot wire the coil to the battery directly with 12 V. Great way to hot wire the rig without a key, don't know how that theory is going to change the ignition problem should it be a ground.
Yes, with the key in the "run" position you should have 12VDC at the coil's red + wire (give or take a volt or two depending on the type of ignition system you have; some used a ballast resistor that dropped the voltage a little). By running a temporary "hot wire" you can supply the coil with a constant voltage and bypass the ignition switch and associated wiring. If it runs without dieing your problem is in the wiring to/from the ignition switch or the switch itself. I would still double check grounding of the ignition module first though.
I was always under the impression that the stock location of the ignition module was on the pass side fender well... I must be mistaken, in any case, yes that is the ignition module and it is grounded using the bolts that attach it to the fender. I also believe there (in some cases) was a black wire that came off the module and provided an alternate grounding location. If I was you I would back the bolts that hold the module down out a bit and install a star washer on one or two and then retighten them. Once you tighten them down, take a resistance check from the negative terminal on the battery (or a good ground point) to the ignition module case; you should have a very low resistance reading (I.E. 0 Ohms). If this doesn't solve the problem inspect the connectors and wiggle the wiring (at the module, coil and under the steering column near the ignition switch) while it's running to try and duplicate the intermittent problem; when it dies you will know your in the area of the problem. Hope this helps and good luck, these types of problems are a pain to isolate and correct....