What would cause the tach to read incorrectly?

[mancini_mark]

Hi guys,

I'm trying to figure this oune out. I got a used instrument cluster from ebay. It's a 1993 and my car is a 1990. Since it was in miles per hour, I had to use my gauges. Everything works and reads correctly except for the tachometer, which reads 1000 RPM too low on the highway.

What could cause this? If it were the speed sensor, wouldn't the speed be wrong also? Or does the tach rely on a different sensor? Could my tach be defective or incompatible with the 1993 SI board?

Thanks,
Mark

[632 Regal]

guess I'll throw in my 2¢

I would think it has something to do with the capacitors in the cluster, maybe you can compare them against each other and isolate the non-conformist and solder that to the new board. It's just a guess but I give you something to think about, hope you get this figured out.

Jeff

[ryan roopnarine]

a voltage regulator for the instrument console....if you have already tackled the capacitors and stuff.....fords sometimes develop a lagging tachometer with a failed instrument regulator.....(called autozone for alternator regulator, told me only thing they had was for instruments, go figure)....i don't know if the fact that you have an m20 i guess??? and its from a 93 in which only a m50 would be, would play a part.

[mancini_mark]

Thanks guys. I got a pretty good deal on this cluster. But I guess sometimes when you cut corners it ends up costing more. So, I should probaby buy a 1990 cluster and sell this one.

Mark

[ryan roopnarine]

which car/engine do you have? might not make a difference, it might just be something like the voltage regulator thing i mentioned.

[mancini_mark]

Hi Ryan,

I have a 1990 525i with the M20 and a 5-speed. Does the car have a voltage regulator that needs replacing or is it something I have to add. If I have to add it, where does it go?

Thanks,

Mark