1986 7k Tach not working

[cdl723]

Recently i completed an engine swap from a M20B27 to M20B25, i swapped the gauge cluster from the 5k Tach to 7k and with the m20b27 everything worked fine, although when it showed 7k it was really 5k with the m20b27. Now with the m20b25 it says it idles at ~400rpm but everything sounds fine. When i rev it up it will go up to about 4k in 1st with a 4.1 diff to about 25mph then drops to 0 when i let off of the gas. also when i rev it up while not moving it goes up then drops immediately to 0 when i let off of the gas. I dont believe this gauge cluster has a coding plug and i had to wire in the c104 connector for ecu power a tach signal and the econo-meter.

[jeffnhiscars]

My understanding is that the early clusters had no coding plug and will not work with motronic 1.1/1.3.

[cdl723]

My understanding is that the early clusters had no coding plug and will not work with motronic 1.1/1.3.

i believe it is out of an 87-88 because it is a VDO cluster and not motomoeter

[jeffnhiscars]

I have 2 87s both with Motometers, my 84 had an early VDO and the 89 and 87 I sold both had VDO so I don't think the make tells you what year it came from.

My understanding is that if the coding plug is in the front it's late and you cannot interchange early and late. Brand doesn't matter.

[cdl723]

i tried a different gauge cluster but it is doing the same thing as the previous. i still am using the same coding plug out of an eta motor.