Hey! My engine's missing!

[RagTop]

I've got a 308 (302 .040 over) and a C4 with a shift kit installed. This setup has been in the car for many years. Today I took the vert out on some back roads and, when there was no traffic, stopped, manually shifted it into "1" and nailed the throttle. I watched the tach and when it hit 6 grand, I shifted to "2". The rpms dropped off to around 4,500 and I nailed it again. At around 5 grand it began acting like it was missing and at around 5,200 the tranny shifted itself into "D". I've run the car in the past at the local drag strip and never had this happen. What's going on? Is there something in the car's vacuum system that is causing the miss and the override shift? I did replace the vacuum modulator on the tranny some years ago, but I can't remember what I was trying to fix at the time. Vagaries of old age. Any suggestions on what could be causing this?

 

[RagTop]

Well, thanks for all the suggestions and comments. They were invaluable. I went out and purchased eight Autolite 104 plugs and pulled the old ones. After 48K miles the electrodes showed almost no wear and all eight plugs were light brown in color. Hats off to Pertronix and their excellent Flame Thrower coil. I installed the new plugs and, after correcting two wires that I must have crossed, the car is running flawlessly. Thought I'd pass that along since you guys were obviously deeply concerned about the outcome. Thanks again.

 

[AzPete]

Glad we could help.....

 

[Horseplay]

Sorry so late to the party. I'd check the plugs and wires.