I decided to undertake the cluster swap in my '97 and in my research, it was made clear that the tachometer would read high and the scale would be off. Since the 99+ CTO signal operates within a range of 43-200Hz and the 94-97 CTO signal operates within 130-720Hz, some sort of modification is necessary. What wasn't clear in my research was how to properly fix it and the correction seemed to be a closely guarded secret on the forums for some reason.
I disassembled cluster, examined the PCB, and found the datasheet tach driver IC (CS4121). In following the calculations for the trim resistor, I learned that for us 97/98 owners, we must simply short (read: bypass) R19. The trim pot will then allow you to adjust your tachometer to the appropriate range.
I've read in several posts suggesting the installation of a 10k Ohm or 100k Ohm resistor inline with the CTO signal. This is unnecessary and if you have one installed, remove it.
As seen in the pictures below, I simply soldered a piece of wire across the resistor. Hope this helps you guys out! Now if only I could figure out how to reprogram the speedometer driver to correct my VSS signal .
R19 Replacement:
Adjust this trim pot:
Swapped:
Idle:
1000:
1500:
2000:
I disassembled cluster, examined the PCB, and found the datasheet tach driver IC (CS4121). In following the calculations for the trim resistor, I learned that for us 97/98 owners, we must simply short (read: bypass) R19. The trim pot will then allow you to adjust your tachometer to the appropriate range.
I've read in several posts suggesting the installation of a 10k Ohm or 100k Ohm resistor inline with the CTO signal. This is unnecessary and if you have one installed, remove it.
As seen in the pictures below, I simply soldered a piece of wire across the resistor. Hope this helps you guys out! Now if only I could figure out how to reprogram the speedometer driver to correct my VSS signal .
R19 Replacement:
Adjust this trim pot:
Swapped:
Idle:
1000:
1500:
2000: