Mustang 5.0 No Check Engine Light Problem - Ford Mustang Forum
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post #1 of 2 (permalink) Old 02-24-2007 Thread Starter
lbones's Avatar
Joined: Feb 2007
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Mustang 5.0 No Check Engine Light Problem

Hello all,
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).

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post #2 of 2 (permalink) Old 02-24-2007
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Hmmm. Well, I'd disconnect the tach. Did you hook it up per the '92 schematic? - Like the factory one in a '92?
If it's an aftermarket tach, like a Sun or something, I'd follow its instructions.
If it's a RalleyPac, I guess I'd hook it up, like you would, an aftermarket one.

'88 GT convertible, 5 speed, 3:08 gears, A9L Mass Air conversion. Mac shorty headers and H-pipe, Magnaflow catback.
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