What is the Ford IDM (Ignition Diagnostic Monitor) signal?

The IDM signal is sent from the TFI module to the control module as a check of ignition function, using the same pin that sends the signal to the coil and tachometer. The control module compares IDM with SPOUT to verify the coil signal matches; if not, the ignition system probably has a fault and the Check Engine light is turned on with a trouble code stored.

How does Ford's push-starting ignition mode work?

The control module recognizes push starting as a relatively low rpm signal (as if cranking) but with no START signal. It modifies output for stronger spark under low-battery conditions by providing longer dwell for greater coil ON time. In push start, the coil is fired by the rising edge of the SPOUT signal for maximum coil charging.

What does 'SPOUT is the shout, IDM is the echo' mean?

It is Ford's description of the ignition check: the control module sends the SPOUT signal to the TFI module, and the IDM signal echoes back so the module can verify the coil signal matches the commanded SPOUT signal.

What is TFI Computer-Controlled Dwell (TFI-CCD)?

TFI-CCD, first used on the 1989 3.0L in California and on most Ford systems by 1992, computes the timing of closing the coil primary circuit so primary current rises to the proper level exactly at the moment of opening. Higher rpm requires closing the circuit sooner; CCD uses PIP inputs and delivers less energy into the coil to reduce overheating.

What is the TFI-IV Closed-Bowl Distributor (CBD)?

TFI-IV Closed Bowl identifies a distributor design on 1988–90 3.8L engines. The distributor bowl is closed and the TFI module is remotely mounted; one PIP signal (PIP-B) goes to the TFI module while a second (PIP-A) goes to the control module along with ignition ground and the SPOUT signal, passing through a grounded shield.

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Ford TFI Ignition Waveforms: PIP, SPOUT, IDM Signals - Push Start & CCD Dwell

TFI ignition control strategy and Ignition Diagnostic Monitor signal waveform diagrams, manual page 122

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Manual page on Ford TFI ignition control strategies explaining PIP, SPOUT and IDM signals with push-start and Computer-Controlled Dwell (CCD) waveform timing diagrams.

AI caption July 2011 · Photo 160 of 224

This is page 122 of an automotive reference book chapter titled "Actuators—Implementing Control Strategies," covering Ford TFI (Thick Film Integrated) ignition system operation. The text explains how the control module uses PIP (Profile Ignition Pickup) input, along with ECT and EGO sensors, to calculate spark advance and send a SPOUT signal to the TFI module. It describes the Ignition Diagnostic Monitor (IDM) signal, which the control module compares to SPOUT to verify ignition function — summarized by Ford as "SPOUT is the shout, IDM is the echo" — with Failure Mode Effects Management (FMEM) invoked for serious faults. The page details Push Starting mode, where longer dwell compensates for low battery voltage, and contrasts it with Computer-Controlled Dwell (CCD). Fig. 3-4 (reference B2212-A15100A) shows oscilloscope waveforms of IDM, SPOUT, and PIP signals (including the Signature PIP) for both push-start and CCD modes. Additional sections cover TFI-IV with Closed-Bowl Distributor (CBD) used on 1988–90 3.8L engines with remote-mounted TFI module and dual PIP signals, and TFI-CCD, introduced on the 1989 3.0L in California and standard on most Ford systems by 1992, which computes primary-circuit closing time based on rpm to charge the coil properly while reducing overheating.

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Frequently asked questions

What is the Ford IDM (Ignition Diagnostic Monitor) signal?: The IDM signal is sent from the TFI module to the control module as a check of ignition function, using the same pin that sends the signal to the coil and tachometer. The control module compares IDM with SPOUT to verify the coil signal matches; if not, the ignition system probably has a fault and the Check Engine light is turned on with a trouble code stored.
How does Ford's push-starting ignition mode work?: The control module recognizes push starting as a relatively low rpm signal (as if cranking) but with no START signal. It modifies output for stronger spark under low-battery conditions by providing longer dwell for greater coil ON time. In push start, the coil is fired by the rising edge of the SPOUT signal for maximum coil charging.
What does 'SPOUT is the shout, IDM is the echo' mean?: It is Ford's description of the ignition check: the control module sends the SPOUT signal to the TFI module, and the IDM signal echoes back so the module can verify the coil signal matches the commanded SPOUT signal.
What is TFI Computer-Controlled Dwell (TFI-CCD)?: TFI-CCD, first used on the 1989 3.0L in California and on most Ford systems by 1992, computes the timing of closing the coil primary circuit so primary current rises to the proper level exactly at the moment of opening. Higher rpm requires closing the circuit sooner; CCD uses PIP inputs and delivers less energy into the coil to reduce overheating.
What is the TFI-IV Closed-Bowl Distributor (CBD)?: TFI-IV Closed Bowl identifies a distributor design on 1988–90 3.8L engines. The distributor bowl is closed and the TFI module is remotely mounted; one PIP signal (PIP-B) goes to the TFI module while a second (PIP-A) goes to the control module along with ignition ground and the SPOUT signal, passing through a grounded shield.