than he must have a TBI,usualy two main injectors I have seen them run rich in the past at the shop I worked at but that was on a 98 chevy suburban. To fix we had to replace an 02 sensor and update the trucks computer(recall). It could be an 02 sensor but its not tripping a code I have also seen that on a couple of dodges.

1986 Isuzu Trooper 2.3
2004 Suzuki GS500F