I have been trying for what seems like an eternity now to diagnose a problem with my 89 4x4 Toyota (22re). The truck, on occasion and without warning, cranks but won’t run but after it sets a few hours, it always starts. The “Check Engine” light doesn’t illuminate during key-on or during cranking when it doesn't start. I have checked for spark and it is there. I can always tell when it is going to start as the light comes on in the key-on position. I've used starting fluid but it only runs as long as it takes to burn it up. I checked the code and it set at 51. It has a new AFM, Coolant Temp Sensor and ECU so they can more than likely be eliminated. I am certainly no mechanic, but it seems as though the problem is in the secondary ignition. Any help on where to start and what to check would sure be appreciated. Thanks.