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EFi tickover and mixture setting

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  • EFi tickover and mixture setting

    When I took my car for its MOT the co2 was very high and wouldent pass the emissions, so they tweaked the screw down to 4% to get it to pass, however since then its made the tickover a bit lumpy and oddly smells quite rich from the back, I know which is the mixture screw and the tickover screw but I doubt you just turn them to set it, is there a correct procedure to do this?

  • #2
    Originally posted by Mikey v8 View Post
    When I took my car for its MOT the co2 was very high and wouldent pass the emissions, so they tweaked the screw down to 4% to get it to pass, however since then its made the tickover a bit lumpy and oddly smells quite rich from the back, I know which is the mixture screw and the tickover screw but I doubt you just turn them to set it, is there a correct procedure to do this?
    Hi I wrote this a while ago but it outlines the procedure you need to set up your EFI. If you follow all the steps it should sort your problem.

    I would recommend cleaning the throttle body out before you reset the idle speed CO setting and most important the throttle pot setting, as the ecu needs to see this information in order to correctly control the idle speed. If you have previously tampered with the base idle screw then the throttle pot setting will definitely be wrong now.

    The best way to clean the throttle body is to remove the throttle body and unscrew the stepper motor, then give it a good clean with carb cleaner to remove all the gunk that accumulates around the throttle butterfly. You will probably find the small breather port needs unblocking as it is nearly always blocked.

    To set the base idle the engine needs to be hot. Then you need to ensure the stepper motor is fully closed (there is a special tool for this) but you can do it by using the following method.

    Turn on the ignition and wait 10 seconds then remove the stepper motor plug, then turn off the ignition and wait 30 seconds or until you hear the main relay click out. Then replace the stepper motor plug and turn on the ignition and wait 10 seconds, and then remove the stepper motor plug again. Turn off the ignition and wait 30 seconds etc. Then repeat once more this will ensure the stepper motor is fully closed. With the stepper motor plug disconnected start the engine and set the idle speed to 650rpm with the throttle stop screw, always make sure all electrical loads are off i.e. HRW, lights, blower, radio, engine cooling fan etc when setting base idle. Then replace the stepper motor plug.

    After setting the base idle you will need to reset the throttle potentiometer with a voltmeter to read 325mv output with the throttle closed with ignition on. The throttle potentiometer setting on the Maestro and Montego 2.0EFI with Lucas hot wire fuel injection is a very important setting and is crucial to the correct running of the engine.

    To set the throttle potentiometer you will need a suitable multi–meter and an allen key or angled pozi–drive screwdriver.

    There are three wires going to the potentiometer from the fuel injection ECU The harness wires are coloured as followed: pink with black trace, pink with purple trace and a third which varies from model to model and is either green with red trace or green with yellow trace.

    With the ignition switched on and the throttle potentiometer harness connected push the probe of the black wire of the multi – meter into the pink and black wire of the vehicle harness throttle potentiometer connector. Then push the probe of the red with of the multi–meter into the green and red wire of the vehicle harness throttle potentiometer connector. If your harness has a different colour wire always remember that the pink and purple wire is never connected into with the meter.

    With the multi – meter set to the mv setting measure the voltage reading. The reading should be 325mv +/-10mv with the throttle fully closed. If the reading is incorrect then the two screws holding the throttle potentiometer to the throttle body can be loosened enough to move the potentiometer to obtain the correct reading. Take care as when the screws are re tightened the setting can alter. Open and close the throttle butterfly a few times to ensure the reading stays constant when the butterfly is closed. I find that sometimes it is easier not to loosen the screws of the potentiometer and just tap the potentiometer body gently with the handle of a screwdriver to obtain the correct reading, obviously sometimes loosening the screws is the only option if more force would be needed.

    Once you have done this with engine at normal temperature set the CO to 2% with the screw on the throttle body nearest the stepper motor, that’s if you have access to a gas analyser of course.

    Regards Gary

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    • #3
      Thanks for that, ill give it a try

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      • #4
        Ok, ive had a go a this today and still cant get it right, once I set the base idle to 650 its fine, but setting the potentiometer is posing a problem. I can only get it to 360mv and its as far over to once side as you can get it, so I set it at that, started the car up and its upto 1200rpm again! Any further ideas? I did repeat the procedure a few times and each was the same.

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        • #5
          Originally posted by Mikey v8 View Post
          Ok, ive had a go a this today and still cant get it right, once I set the base idle to 650 its fine, but setting the potentiometer is posing a problem. I can only get it to 360mv and its as far over to once side as you can get it, so I set it at that, started the car up and its upto 1200rpm again! Any further ideas? I did repeat the procedure a few times and each was the same.
          Hi Mikey V8

          Did you thoroughly clean out the throttle Body before starting the procedure? Thick gunk around the butterfly, particularly on the manifold side restricts the air flow.

          If you can't get 325mv (0.325v) the throttle pot could be faulty.

          The ECU has to see 325mv at throttle closed or it can't control the idle speed.

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          • #6
            I think that is the problem, ive tried to set it too 3.25 not .325, hmm, will try again tomorrow.

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            • #7
              Many thanks for this info. So I started, CO at 2.4% did the idle valve on-off sequence then used the multi-meter on the potentiometer. The reading should be 325mv mine was 008mv !!! there's not much space to get a screwdriver there behind to loosen the screws so I jigged a pair of pliers with a posidrive head and taped the pliers tight............it worked. I got to 325mv very quickly, tightened the screws it changed to 324mv.....close enough finished off the process and I have to say the car drives a whole lot better than before. The throttle hesitation appears to have disappeared. I do own and have used an AR Fast Check unit but you need to keep getting under the dash and back out to car, with the multi-meter it's all done under the bonnet. Will do a double check tomorrow or Sunday, once again many thanks.
              Chris
              Mechelen
              Belgium

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