A9L 12v at pin 46 help? - Ford Mustang Forum
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post #1 of 2 (permalink) Old 4 Weeks Ago Thread Starter
splithigh's Avatar
Joined: Aug 2019
Posts: 2
A9L 12v at pin 46 help?

93 fox, T56 Magnum, A9L

Car was an original AOD with C3W EEC (I still have C3W EEC). Swap was preformed by previous owner with T56 and A9L. I purchased the car and was fighting idle surge problems when cold and when restarting. Reviewed idle surge checklist - Checked voltages at MAF, TPS, IAC and replaced IAC and TPS, base idle reset,replaced all vacuum hoses. KOEO codes 15, 85, 67 and 66c. Eliminated 15 with check sum base set to 0 with Tweecer. 85 due to no purge installed, 67 is NSS so I started chasing this code. Still have 67 code with clutch in while running test. 66 may be due to car surging badly and low voltage as it almost dies (will diagnose further after I get it running again)

Car ran well for years (I knew the person that I bought the car from). It had cold start idle surge but other than that, it ran well.

I could get the car idling well after battery disconnect, drive around for a while (20-30 min) with no issues. Restart minutes later and idle surge returns like there is no memory.

I have been researching many threads and I believe that I have narrowed down some issues.

I am getting 13v at pin 46. A9L disconnected (key on, crank, clutch in/out)

Car had a Auto O2 harness so I re-pinned the loop from NDS pin 30 to Manual on the black connector. (also tried NDS to auto with same result).
Car had a auto trans harness so I replaced it with a new manual trans harness with all 8 wires. T56 will only accept VSS and passenger side 4 wire plug from factory manual trans harness. plug or unplugged - have 13v at pin 46
black and gray clutch switches are installed at assembly. plugged, unplugged, and looped NSS with fuse - all still 13v at pin 46.
Car has push button start under dash (previous owner wired directly to ignition in engine compartment) key does not start car. replaced ignition switch. Still does not start with key, only starts with push button.

Disconnected all sensors associated to pin 46 connections per wiring diagrams, NSS, clutch switch, tps, O2 harness, Baro, intake temp N/A, EGR N/A, engine coolant sensor N/A - checked pin 46 volts at each disconnect and with all disconnected including the trans harness - Still have 13v at pin 46

Removed pin 30 at EEC harness and grounded at chassis - Still have 13v at pin 46

I inspected the A9L and do not see any signs of burnt connections. Not sure how this did not originally fry the A9L as the car was running for years with auto harnesses (O2 and Trans). Most say that this will burn the EEC??

Any ideas on why I am still getting 13V at pin 46? Thank you for your help.

Update - I disconnected the brown 8 pin connector next to the brake booster and that resulted in 0v at pin 46. This harness appears to go under the drivers dash. From everything that I have read, I do not want to plug in the ECU with power to pin 46 however, I believe the car had been running like this for years. I don't believe anything I did added power to pin 46 (i.e. adding a manual harness and correcting the loop at the O2 harness) because I still have 13v at pin 46 when these are unplugged.

Any help would be greatly appreciated.

93 Notch, 408ci, T56 Mag, Tweecer RT

Last edited by splithigh; 4 Weeks Ago at 05:22 PM.
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post #2 of 2 (permalink) Old 4 Weeks Ago Thread Starter
splithigh's Avatar
Joined: Aug 2019
Posts: 2
I figured out my problem! My stupid mistake! I ran resistance test on all pins to the self test connector where pin 46 terminates and I had the harness flipped and was originally testing pin 15 which has power at start. If you flip the ecu harness 15 is in the same position as 46. Lesson learned, review diagrams closely for correct pin-outs.

93 Notch, 408ci, T56 Mag, Tweecer RT
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