Mustang 5.0 No Check Engine Light Problem
I have a '92 A9P EEC up and running in a '66 Mustang. I finally got around to hooking up my tach today according to the '92 wiring diagram. With the tach hooked up the engine idles at 1800rpm, cold or hot. I guess the tach being wired in is causing the eec to advance the timing or something? With the tach disconnected it idles fine.
The other problem now is that the check eng light does not come on when I turn the key on, and will not flash if I try to read codes (to see if I have any now!) This no light situation did not occur until I first hooked up the tach.
The engine runs great but I want the check engine light to flash codes for future diagnostics, and of course I want to run a tach! Any help with this weird situation would be most appreciated. Everything is wired correctly and the eec/check eng light ran a code test normally before this damn tach hookup (flashed back as no-codes present).