GM HEI help with diagnosis

[CampbellCarl]

Brian
Can you tell me how/where to test for ignition and spark? '78 Howard V-drive, BBC LS-6, previous owner installed the HEI distributor. Have fuel but I guess no spark.
Thanx
Carl

[BDMar]

Brian
Can you tell me how/where to test for ignition and spark? '78 Howard V-drive, BBC LS-6, previous owner installed the HEI distributor. Have fuel but I guess no spark.
Thanx
Carl

The GM HEI distributor typically has thre wires going to it. The ign 12v, tach wire, and ground. Remove the 12v wire from the dist., turn on the key to "run" position and check for 12v. If there is power to the wire turn off the key, re-connect the wire and pull a spark plug. Put the plug wire back on the plug, ground the plug threads against the block and turn the engine over and look for spark at the plug. If there is no spark it is either the coil or ignition module. 90% of the time it is the module. Don't forget the obvious and remove the dist cap and check for a broken rotor or cap.

[CampbellCarl]

Thanx Brian. I did the easy checks, have 12v to distributor and nothing to the plugs. I pulled the module and coil. Funny thing I noticed, the coil ground wire was routed to a screw that did not direct connect to the grounding 'tab' in the cap housing. I suppose that the ground could make it's way around the coil case and to the screw hole that direct connects to the tab.
CC

[BDMar]

If it has always been that way I would have to assume it has been getting a good ground and that is not the problem. I would move it to the correct spot. At this point we would put in out test ign module and re-test. There is no guaranteed test for the ign module that I know of. There are troubleshooting "trees" you can follow, but they are going to lead you to the point you are at. It will say replace the coil, then if it doesn't work it will then tell you to replace the ign module. Try also with the tach wire disconnected. I have seen bad tachometers cause this also. I am still betting on the module.