OK, I'm pulling out what little hair I have left over this. 1985 2.8L multiport injection. My mass air flow meter signal voltage will not change when running, and it stays in open loop. With the sensor unplugged I have the 5 volt signal, but as soon as I plug it in it drops to 2.5v. I've tried one rebuilt and 2 brand new MAF sensors. I've checked and cleaned all grounds, battery to engine, engine to body, body to battery, and MAF sensor ground to body. Also have cleaned and checked connection at ECM, ran a bypass wire from sensor to ECM, and have even put in a rebuilt ECM. There is something obvious I'm missing, what the heck is it?