I have 305 VIN F iroc that seems to misfire under load, but not consistently. Sometimes its coming out of first, sometimes second. The car gives a huge buck.

I changed the spark plug wires (which I’ve been needing to do either way), drove it for a hard lap around town and on my way home, it had two instances of a misfire. They don’t last long. It gives one buck and I push in the clutch. I get back on it and its fine.

The plugs have less than 20,000 miles on them. Wires are MSD. Im wondering if a worn cap/rotor or coil could cause this issue? The misfire is not consistent, so I don’t really know how to trigger it for troubleshooting yet. Anybody have any ideas?

 

Does it only happen when you get on it? Is it okay at light throttle and cruise? If it is, I'd go after the ICM under the Dist cap.

 

it happens whether I get on hard or not. It hasn’t happened when cruising, just under acceleration

 

Change that ICM.

 

Did you ever get this problem fixed you were having? If you are having some kind of intermittent electrical problem it might not be a normal engine misfire but the engine cutting out for a fraction of a second seeming like a misfire.

Starter cranks first try only on cold starts - Third Generation F-Body Message Boards

 

Too many things it "could" be.

You already replaced the plug wires. Plugs are cheap. Change them and set the proper gap.

Not sure about ignition, Large cap or computer controlled? Either way, new cap and rotor are worth a try. Large cap distributor, you may not like it but replace the whole distributor. Its probably still original and they do wear out.

Not saying yours is the same but I had an old GMC truck with a similar problem. Older truck with a large cap distributor. Light acceleration and it drove just fine but if you put your foot to the floor to accelerate, it would cough and sputter before picking back up again. Turned out the pickup coil wires inside the distributor were dried out and cracked. Every time vacuum dropped when the throttle was put to the floor, the vacuum advance would adjust the timing which would rotate the timing plate, pull on the pickup coil wires and break the connection. When the engine would start to miss, the vacuum advance would change, the wires would reconnect and the engine ran fine. Took me a while to figure that one out.