1977 Questions for all other cars 1977 International Cargost

TFS MAN

MEMBER
1977 ALL OTHER MAKES ALL OTHER MODELS

1977 Questions for all other cars V8 Two Wheel Drive Automatic

I can't get good enough spark at plugs to fire. The truck would not start one day. It was found that the pick-up coil in the dist. Was bad and replaced. It was sending signal fine after that and we got a small amount of spark at coile wire, but not enough to fire. The ign coil and ign. Module were both replaced and still have the same problem. It sparks really good with key on and off but when in crank mode, very weak. We have good power at pos term of coil, we have a good signal to neg terminal as it flashes with test light as we crank. We have ignition power to module. There is a white wire coming off module that was previously cut and leads nowhere but the truck has run fine this way. We did put a 3.5ohm internal resisted coil on to replace the 2.4 ohm coil that was on before. The problem was that the non-internal res. Coil had no ballast resistor in the system. Again, the truck ran fine this way but thought we would eliminate this as a possible problem. The spark at the coil wire can't jump but about.0020 and hasn't enough energy to make it to the plugs. Grounds are good. Powers are good. We have tried 3 different igntion modules with same results. What is going on?

1 Reply

HMAC300

MECHANIC
48,601 POSTS

From what i've read, you replaced the coil with an internal resisted coil and the old one wasn't. You should go with what was on the truck to begin with. You must check to see how much voltage is coming to the coil with thekey on. If it is lower than 12 volts you may just not have enough voltage being created with the 3.5 coil. Alot of vehicles have lower voltage either through the wiring harness or a resistor to cut the voltage to the coil. It should have 12 volts when cranking then cut down to 9 or so when running. I would really look at the inside of the distributor/rotor cap for carbon tracing and leaking inside the cap, not allowing the spark to go any further than the coil wire placement. This is the only thing I can think of with your description.