Hello,

About nine months ago, I rebuilt the engine on my 1988 744 Turbo. (Automatic Transmission) Everything has been running very well since then. Since that time, the only thing that was replaced was a poorly functioning fuel-pressure-regulator. The car shifts well and the engine is quiet, however, I am extremely doubtful of the tachometer's accuracy.

99.9% of the time, the tachometer I think the tachometer reads too fast, and it bounces around too much. Since I rebuilt the engine, I have been a bit weary about the tachometer. For a long time, I was hoping to find some reason disprove the tachometer. This summer has been the perfect time. For some reason, a few times this summer, the tachometer will seem to be slower, it seems to be more in sync with the engine, or at least it sounds to be. This has happened on a few days when the car is really hot. For example, it has been sitting out in the sun for a long time or it has been driven a lot. This has only happened about 4 times this summer. I have noticed it when the car was under the conditions mentioned above and I popped the transmission into neutral. To make it stranger, this would happen more often than not when the transmission was popped into neutral. After this experience, I could cruise down a few roads at 75 - 80 mph with the tach reading about 2.5k - 3k vs. 4.5 - 5k. (The engine would not sound any different based on the tach reading.)

--Any suggestions?

--Is the car supposed to run that fast?

--Are both conditions inaccurate?