Help, making a video about EVAP troubleshooting

Discussion in '3rd Gen 1997-2002 2.0L SOHC' started by Adamprince2, Dec 31, 2016.

  1. Adamprince2

    Adamprince2 FEOA Member

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    I'm making an in depth video about EVAP troubleshooting and repair for the 1997 Ford Escort. Which has a different system from the later models.

    Anyhow, one thing has confused me. With the key ON and the engine OFF the purge solenoid has 12 volts supplied to it. I have confirmed this with an voltmeter. However, on my car a known good solenoid does NOT open under this condition. I have confirmed this with a vacuum gauge. I also confirmed the solenoid does open when directly connected to the battery. I also disassemble the connector and there was no corrosion. The wires are supplying voltage, but no apparent amperage (did not measure).

    Is this a normal condition? If so, what is the purpose of the 12v with the key ON and engine OFF?

    Thank you, I know you guys are really helpful.
  2. denisond3

    denisond3 Moderator Staff Member

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    I have no clue - other than that perhaps the other contact to the evap solenoid gets grounded to make it open, rather than one contact being grounded all the time. I think that is the way the injectors work. Each one has 12 volts to one contact, and the computer grounds the other contact to make the injector 'squirt'.
  3. Adamprince2

    Adamprince2 FEOA Member

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    So can the computer supply a ground with the key ON/engine OFF, but vary the resistance of said ground to control whether the solenoid moves or not even with 12v present? Or is PCM the defective? I ran a bunch of tests.

    A bulb lights when connected to the negative battery post with the other side connected through the power side of the solenoid connector. Additionally, when a wire is run from the negative post of the battery to the ground side of the back of the purge solenoid connector the solenoid clicks.

    A wiring check from the solenoid connector to the PCM connector with the PCM disconnected shows 0 ohms on the power wire and about 2 ohms on the ground wire.

    I also checked for a short circuit by removing the solenoid and checking the ohms on the circuit from the PCM connector. The reading was out of range. I checked again with the solenoid connected (to confirm I had the correct circuit). I read about 55.1 ohms and the solenoid itself if disconnected reads 52.4 ohms.

    A check of the ground from the solenoid connector (with solenoid removed) to the negative post of the battery with the key ON and engine OFF (PCM reconnected) shows a resistance of 6560 ohms.
  4. denisond3

    denisond3 Moderator Staff Member

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    I think the solenoid is only operated by the PCM when the engine is running and warmed up, and the car is being driven along the highway. But my Escorts are all 2nd generation ones, and may be setup differently from 3rd gens.
  5. bent_rod

    bent_rod FEOA Donator

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    I agree with denisond3 about the operation of the purge solenoid.
    I looked in my 1998 Ford manual and found one side of the solenoid is connected to 12V by way of the 10A Injector fuse. It is hot with the key on and with key in the start position. The computer supplies ground to operate the purge solenoid when purge conditions dictate.
  6. Adamprince2

    Adamprince2 FEOA Member

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    I wanted to report back. I thoroughly examined my system. The PCM supplies 12 volts to the connector with the Key On and Engine Off. It also supplies a high resistance ground, which is enough for a voltmeter to read 12V on the connector, but does not supply enough amperage to move the solenoid.

    The solenoid does NOT operate at idle. I confirmed this using a scanner. I also observed the solenoid operating when the engine is driving. The computer is supplying the high resistance ground with key on, engine off for trouble shooting purposes.

    Another quirk of the system is that if a light bulb is put between the solenoid wires (Pin 71 and Pin 67) while the car is driving it will cause the computer to throw a P0443. However, if voltmeter is put between the solenoid wires and set to AC volts (not DC) you can see the output vary between 6V to 10V cruising around 50 mph.

    I published the video to Youtube and will post a link to the general forum. It covers P1443, P1444, P1445, and P0443.

    Thank you for all the HELP!
    denisond3 likes this.

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