dei and failed remote starts

Black key definitely does not have a transponder, like you said. They made plenty of Liberties both ways. Where is the remote starter's tach wire connected? It should be ok to be tied into a fuel injector on top of the engine. Even if you don't want to go with voltage sensing, it's an excellent temporary troubleshooting tool...........you could reprogram for voltage sense, with 1.0 seconds crank time, and see if it works reliably for a couple of days. At least then, if it does work fine on voltage sense, you know that the rest of the installation is good, and that it must be a tach issue for sure.