My uncle's van has a 4.3 w/ TBI in it, but TBI is TBI, regardless of engine. The timing, if set on 0 degrees with the connector disconnected, makes the engine run bad, it likes it more around 12 degrees before TDC. However, when running smooth, you hit the gas and the truck stumbles and vibrates. Timing chain's been checked, it lines up perfect. Distributor did not spin. What could this be? It was running fine, then we took a turn and it died on us. 3 weeks later, we've finally gotten it to start.