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Zetec Drivability Problem

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  • Zetec Drivability Problem

    Lately I've been experiencing a drivability problem with our stock Ford Zetec VVC ('98 Ford Contour) powered Seven. The symptom is missing and rough running at very slight throttle openings, similar to what I'd expect from an engine running too lean. The symptom is most noticeable when backing off the throttle to maintain speed after accelerating. At large throttle openings, the engine runs smooth and produces normal power.

    At first I thought the problem was a malfunctioning Throttle Position Sensor, and replaced that with a new Ford unit, but to no avail. I've also cleaned the Mass Air Flow sensor (with the proper cleaner) and also the throttle body (again with the proper solvent).

    As with most of the '98 Ford Contour Zetec powered Sevens (at least those I'm aware of), my engine's idle speed has almost always been high (1,200 - 1,500 rpm), but recently has been a little more erratic than in the past, sometimes falling to 500 rpm, and other times remaining at 1,600+ rpm. One thought is the Idle Air Control valve is sticking open when it should be closed and allowing excess air to the engine when the throttle is nearly closed, thus causing the lean / stumbling condition. Or, maybe my PCM is going away and not controlling things properly. Does anyone have any advice or experience to help sort this out?

    One of the things that makes this condition particularly difficult to diagnose is a problem reading the PCM error codes. The Snap-On code reader/diagnostic tool that most shops (and earlier, the BAR Referee!) use will not communicate with my car's PCM! I took the car to a Ford dealer once, and his diagnostic device did communicate, AND we got lots and lots of error codes since the Zetec installation in the Seven is so different from that in the Contour. Maybe that should be my next step in this search. But, has anyone experienced this problem and found a solution to accessing the error codes without going to a dealer?


  • #2
    Clark, take a look at:

    My first Birkin (the yellow one) had a stock zetec with a 97 Contour ECU, and the Scan Tool worked well at reading codes. Like you said, there are so many codes generated due to our unorthodox installation.

    If you think you need to replace the ECU, I found a spare on ebay for about $25 for the same year Contour, and it worked well. Sorry, but I don't have the ECUs (or the Scan Tool) anymore.

    Good luck, I know how frustrating these things can be!



    • #3

      ECU's usually fail quite fatally; they either work or they don't. In some cases you burn out an input to the ECU where a single channel (throttle position etc) dies, but this is not very common.

      I'd say that you either have a leak between the throttle body and the engine, or that the idle bypass valve is stuck. Spray small amounts of starter gas on the intake manifold when the engine is cold (so that you don't burn down your garage) and check if it revs.

      The idle bypass valve is quite commonly stuck since it is a mechanical part that is not lubricated by the engine. (The valve is a small extra throttle controlled by the ECU, which can use it to let extra air into the engine at idle. It is spring loaded to a closed position by default, but can be pulsed open in several steps using a 50Hz (or was it 100Hz?) PWM signal from the ECU.)

      Remove the valve and check that it opens and closes smoothly. If not, WD40 is your friend. You can probably also turn on the ignition and even crank the engine with the valve out and plugged into the harness to see if it moves. You may even be able to run the engine without the valve if you plug the hole somehow. I've never tried this, though. If the valve moves smoothly but does not react to ECU input, the coil is probably fried. Ebay a new used one.

      If you want to hook up, we can plug one of our M1 units into your car and get real time readings of all the sensors to see that they work as they are supposed to.

      /Magnus F.
      Last edited by magnusfeuer; January 22, 2008, 10:53 AM.


      • #4

        Check the plug for the mass air flow sensor to wiring harness. Mine broke and produced similar symptoms if not fully connected. I bought a replacement pigtail from Ford or an aftermarket company.

        A standard scan tool should read the PCM codes. The codes caused by the Zetec being installed in the Caterham tend to be from the carbon canister, fuel tank, automatic transmission etc. that the PCM expects to see but is not used on the Caterham.

        If the code is from a sensor known to be used, as the MAF, that would be where I would check first.

        I have a scan tool you can use but am out of the state until Friday.

        Also a PCM that I am not using.