What have I scr...messed up now?

[cew5534]

I swapped out auto transmissions in my 1990 240SX. now I have a error code 21 "Loss of ignition signal on primary coil" No Spark, thus no start.

[Ni2s4s0aSnX]

There is no way that a transmission swap could cause an ignition problem. So give me some more information on what the problem is.

[slipnfall]

On your ignition coil/transistor module: there's two connectors(at least on the DE engine): one for the transistor, the other is a condensor/resistor pack. When you key-on, the ECU sends a signal to the condensor pack. The module in return sends a signal back from the power transistor. So either you aren't getting the signal from the ECU, or aren't sending one back. I'll have to dig around in the KA24E service manual to give you specefics. But this is where you need to start.

BTW it is only a code 21, right? not 21 and something else(which could point to a different problem).

HTH,Jamie