| Following up here vs our email for the benefit of others in the future. I looked at the 91 FSM and see that the engine speed signal is fed to the tach and the HICAS controller. The FSM talks about the self diagnostic procedure at length and several of the steps have you above and below a certain RPM w/o giving a reason why. I expect it has more to do w/ pump pressure than anything else. I didn't see anywhere where the tach it's self is in the HICAS chain. This makes me believe that the root of the issue lies upstream some where before the HICAS controller and Tach, but past where the engineer speed sensor/crank angle sensor is fed to the ECU. This is based on the tach/HICAS having issues in sync w/ each other but you are not having engine trouble. I was talking w/ ZXRider and he thinks you are likely having the PS go into limp mode, but since you are already at speed you dont notice it since limp mode drops the PS assist to the min which is where its at when at speed anyways.
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10:05:44 07/02/23
