Several times in past few days, my wife's beloved, fully-dealer-maintained, ultra-reliable '91 740 went into "Hyper Mode" at start-up.

1. "Hyper Mode" is our family nickname for a loud extra whirring sound from the engine compartment immediately after a normal start.

2. The 740 always starts immediately, "Hyper Mode" or not.

3. Checking under the hood, the extra whirring seems to come from the area of the alternator.

4. In "Hyper Mode" the tach seems to show unusually low revs, compared to following a normal start.

5. In "Hyper Mode" some dash warning lights go on but we haven't been able to record which ones due to the intermittent nature of the problem.

6. The problem is intermittent and there's no evident pattern temperature, time of day, etc. except of course that it is almost impossible to reproduce when we're looking for it to happen so we can report the symptoms <grin>.

7. "Hyper Mode" has always been curable by turning the ignition off, waiting a moment, and then starting. The result is always a normal start.

8. For the past several years, "Hyper Mode" has occurred only several times a year not a worry. The sudden increase in frequency is alarming.

Ideas?

TIA

 

Turn down the warp drive to impulse power and power up the flux capacitor to a later year. Kidding, sounds very strange. I have no clue but a big smile. I hope someone can help you on that one.

 

If it's making a lot of noise near the alternator, it could something as simple as a loose alternator belt. Easy to fix.