Are you sure you have a spark coming from the coil going to the distributor? If so, then I don't think the ECU's your problem. I thought you meant no spark period. If the ECU doesn't drive the power transistor, then you won't get power going to the coil which results in no spark at the distributor.

So you have spark coming from the coil for sure? But no spark coming from the distributor? Have you checked both the distributor cap & rotor & the coil wire for spark? Someone else on here will know more about this as well.

Here's the wiring diagram for a 3.0 (89 but the 90/91's are very much the same as the 89).


As you can see, there's no further control from the ECU between the coil and the distributor. The ECU controls the Power Transistor which drives the coil which in turn provides the Distributor with power.