Could a plugged(semi-plugged) catalytic converter cause a vehicle to start hard(like hot timing) when the engine is warm? When cold it starts fine...It's a replacement Jasper engine with only 25000 mi. on the engine, 105000 on the truck. SEL on a couple of months ago indicated bad converter(forgot the code). Did not run bad until now. I posted earlier and got responses of possible ignition issues. My thanks to all who contributed but I still had the lingering question in my mind as to "can a converter cause an engine to turn over hard when warm?" Thanks for all the responses...you guys are great!!

 

It sure can .

 

I would bet more on too small a battery,starter worn, bad cables, where is the batt ground cable connected? It should be on the motor.