On the IDM plug the ground is pin #26

I copy pasted this but it is put out of the Ford Powertrain and emissions factory repair manual.

FJ1 DIAGNOSTIC TROUBLE CODE (DTC) P1670 and P1668

DTC P1668 and P1670 indicates that a communication error has occurred between the PCM and the IDM.

Possible causes:
Open fuse
IDM relay
Open or shorted IDM enable circuit
Open/short in EF circuit
Open/short in FDCS circuit
IDM powering circuits
PCM

Check for other codes.
Key on, engine off.
Perform KOEO On-Demand Self Test and retrieve Continuous DTCs.

Was DTC P1668 present?

Yes- If DTC P1668 is present, GO to FJ2 . No- If DTCs P1667 and P1663 are set together with or without DTC P1668, GO to FJ6 .

If DTC P1298 is also present, REPLACE the IDM.

If DTC P1667 is also present, GO to KA1 .

If DTC P1663 is also present, GO to KF1 .

If DTC P1662 is also present, GO to NC1 .

If P1670 was set without any other DTC, GO to FJ10 .


FJ2 CHECK CIRCUIT 818 (GY/W) FOR OPEN

Install breakout box; leave PCM disconnected.
Disconnect the IDM harness connector.
Measure resistance on Circuit 818 (GY/W) between PCM Test Pin 48 and IDM harness connector Pin 4.
Is resistance less than 5 ohms?

Yes-GO to FJ3 . No- REPAIR open in Circuit 818 (GY/W). RESTORE system. CLEAR DTCs and RETEST.

FJ3 CHECK CIRCUIT 818 (GY/W) FOR SHORT TO GROUND
Measure resistance between IDM relay Circuit 818 (GY/W) and battery ground.
Is resistance greater than 10,000 ohms?

Yes-GO to FJ4 . No- REPAIR ground short in Circuit 818 (GY/W). RESTORE system. CLEAR DTCs and RETEST.

FJ4 CHECK CIRCUIT 818 (GY/W) FOR SHORT TO POWER
Key on, engine off.
Measure for voltage on Circuit 818 (GY/W) between PCM Test Pin 48 and battery ground.
Is voltage present?

Yes-REPAIR short to power on Circuit 818 (GY/W). RESTORE system. CLEAR DTCs and RETEST. No- GO to FJ5 .

FJ5 CHECK SIGNAL RETURN CIRCUIT 359 (GY/R)
Measure resistance on Circuit 359 (GY/R) between PCM Test Pin 91 and IDM connector Pin 2.
Is resistance less than 5 ohms?

Yes-GO to FJ6 . No- REPAIR open in signal return Circuit 359 (GY/R). RESTORE system. CLEAR DTCs and RETEST.

FJ6 CHECK IDM POWER
PCM connected, IDM disconnected.
Key on, engine off.
Measure voltage between IDM connector Pin 14 and battery ground.
Is B+ present?

Yes-GO to FJ7 . No- GO to NC6 .

FJ7 CHECK IDM GROUND
Key off.
Measure resistance between IDM connector Pin 26 and battery ground.
Is resistance less than 5 ohms?

Yes-GO to FJ8 . No- REPAIR open in IDM ground Circuit 574 (BK/PK). RESTORE system. CLEAR DTCs and RETEST.

FJ8 MEASURE FREQUENCY ON THE EF LINE
Connect PCM to breakout box.
IDM connected to harness.
Set up scan tool as follows:
Connect scan tool to the DLC
Connect test probe between scan tool common and breakout box Pin 77 (ground).
Connect second test probe between scan tool signal and breakout box Pin 48 (EF line).
Select VEHICLE and ENGINE
Select DIGITAL MEASUREMENT SYSTEM
Change level to 4 VOLT DC
Press the link button to choose a PID
Select PID/DATA MONITOR
Select RPM PID
Press START
Key on, engine running.
Measure frequency at 3 different RPMs.

RPM Frequency (Hz)
1000 66
2000 133
3000 200


For each rpm value, does the corresponding frequency match closely to the table?

Yes-REPLACE PCM. RESTORE system. CLEAR DTCs and RETEST. No- REPLACE IDM. RESTORE system. CLEAR DTCsand RETEST.

FJ9 DIAGNOSTIC TROUBLE CODE (DTC) P1316 INDICATES THAT CODES ARE STORED IN THE IDM
Possible causes:
Injector(s) or circuit(s)
Open or shorted IDM enable circuit
Open/short in EF circuit
Open/short in FDCS circuit
IDM relay
IDM powering circuits
IDM
PCM

Check for other codes.
Key on, engine off.
Perform KOEO On-Demand Self Test.
Are IDM or any other codes stored?

Yes-GO to the appropriate pinpoint test. No- GO to FJ10 .

FJ10 DTC P1316 OR P1670, CHECK FOR AN INTERMITTENT OPEN CIRCUIT
Key off.
Install breakout box, leave PCM disconnected.
Disconnect IDM.
Check for intermittent open in the following circuits:
Measure resistance on (FDCS) Circuit 821 (BR/O) between IDM connector Pin 17 and PCM Test Pin 95.
Measure resistance on (EF) Circuit 818 (GY/W) between IDM connector Pin 4 and PCM Test Pin 48.
Grasp the harness close to the IDM connector. Wiggle, shake the harness while working your way back to the PCM, while looking for a spike on the DVOM.
Do all readings remain below 5 ohms throughout procedure?

Yes-GO to FJ11 . No- REPAIR open in the suspect circuit. RESTORE vehicle. CLEAR DTCs and RETEST.

FJ11 CHECK FOR AN INTERMITTENT SHORT TO GROUND
Check for intermittent short to ground on the following circuits:
Measure resistance on (FDCS) Circuit 821 (BR/O) between battery ground and PCM Test Pin 95.
Measure resistance on (EF) Circuit 818 (GY/W) between battery ground and PCM Test Pin 48.
Grasp the harness close to the IDM connector. Wiggle, shake the harness while working your way back to the PCM, while looking for a spike on the DVOM.
Do all readings remain above 10,000 ohms throughout procedure?

Yes-GO to FJ12 . No- REPAIR short to ground on the suspect circuit. RESTORE vehicle. CLEAR DTCs and RETEST.

FJ12 CHECK FOR AN INTERMITTENT SHORT TO POWER
Key on, engine off.
Check for intermittent short to power on the following circuits:
measure voltage on (FDCS) Circuit 821 (BR/O) between battery ground and PCM Test Pin 95.
measure voltage on (EF) Circuit 818 (GY/W) between battery ground and PCM Test Pin 48.
Grasp the harness close to the IDM connector. Wiggle, shake the harness while working your way back to the PCM, while looking for a spike on the DVOM.
Did voltage ever appear on any circuit throughout procedure?

Yes-REPAIR short to ground on the suspect circuit. RESTORE vehicle. CLEAR DTCs and RETEST. No-GO to FJ13 .

FJ13 VERIFY DTC P1316 AND/OR P1670
Restore vehicle.
Clear DTCs.
Cycle key off, than start engine.
Road test vehicle.
Perform KOEO On-Demand Self Test and retrieve Continuous DTCs.
Was DTC P1316 and/or P1670 set in Continuous without any codes in KOEO On-Demand?

Yes-GO to FJ14 . No- REPAIR KOEO On-Demand DTCs. RESTORE vehicle. CLEAR DTCs and RETEST.

FJ14 ATTEMPT TO GENERATE IDM DTCS
Key off.
Disconnect one valve cover connector.
Start engine to generate IDM codes.
Perform KOEO Injector Electrical Self Test and KOEO On-Demand Self Test.
Are IDM codes retrieved?

Yes-REPLACE PCM, RESTORE vehicle. CLEAR DTCs and RETEST. No- REPLACE IDM. RESTORE vehicle. CLEAR DTCsand RETEST.

Since a possible cause is a short in the EF ( electronic feedback )circuit here is the PCM to IDM diagram

And one last pic before I get back to my own project.

PCM connector.
3 ground pin outs that share G103 ground location with the IDM and. Color BK/wt
pin 80 is wt/bk and feeds the IDM it’s siginal