Q: GPS never shows correct heading. Changed display & computer, still no good. on 1999 Acura TL

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Is there a compass of some sort that is not showing correct heading of the car or is there an antenna problem? GPS tracks correctly but is slightly delayed in displaying car postion as it changes.
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All the hardware is factory including the computer and display assy. I replace the PCMCIA hard drive with a compact flash - PCMCIA adapter using a compact flash memory card with 256 meg. The dealer took care of writing the compact flash memory for me and it has worked fine for 8 years now. All of a sudden, the gps won't show the correct heading of the car, it is always pointing east on the dispaly no matter what direction the car is pointing and traveling.