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DME and CPS hep

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    #1

    DME and CPS hep

    does the CPS on the front of the motor (removed for timing belt install) actually supply the ecu with information for running or is it just for diagnostics ( i have read two conflicting theories online). I tested the ohms across the cps on pin one and two and it is coming out at 540 ohms. which as i recall puts it in the good working tolerance.

    Secondly, i believe either i cannot access my DME trouble codes OR... my check engine light is burned out :( any ideas?

    my car is dead in the water after my timing belt change. it was working before starting the timing belt and water pump replacement. trying to bleed the system now but i cannot get the car to fire...

    what are my next steps?
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    #2
    From the knowledgeable jlevie's answer to one of my questions on bimmerforums


    "The crank position sensor provides speed and crank position information to the DME. If that sensor is bad the fuel pump won't run and the engine won't have spark as both of those are controlled by the DME and require timing data from a rotating engine. The Cylinder ID signal, from #6 plug wire, is used for timed injector firing. The injectors are organized in two banks of 3 cylinders and based on timing data from the Cylinder ID signal each bank is fired in sequence. In the absence of the Cylinder ID signal both injector banks are fired simultaneously. The only noticeable affect of a lack of that signal is a slight decrease in fuel mileage."

    Based off of this, check for spark by removing a plug and grounding it to an unpainted steel piece in the engine bay and see if you are getting spark. If there is spark, check the color of the spark

    blue/bright white = good spark
    yellow = weak spark

    If there is spark and it is yellow/weak I would look into the distributor cap and rotor being problematic or a weak coil.

    If there is no spark then have someone crank while you listen for fuel pump operation (might be easiest to remove fuel cap and put your ear up to it (using a hose or whatever you can come up with as a stehoscope can be helpful).

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      #3
      pulled a spark plug and had zero spark....

      Comment

        #4
        Originally posted by TheRival View Post
        pulled a spark plug and had zero spark....
        That would suggest, in the light of the work just done, that you have the CPS and Cylinder ID connectors swapped. Or that you left the rotor out of the distributor.

        Not knowing what car you have, I can't say whether the failure of the stomp test to work is due the DME not supporting it or whether the test is failing because of a bad TPS or burned out CEL bulb. If the car is a 9/87 or later production 325i/is and the CEL illuminates when you switch on the ignition, a failure of the stomp test will be caused by a bad or mis-adjusted TPS. If the CEL doesn't illuminate when the ignition is turned on, replace the bulb and try again.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL

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          #5
          Originally posted by jlevie View Post
          That would suggest, in the light of the work just done, that you have the CPS and Cylinder ID connectors swapped. Or that you left the rotor out of the distributor.

          Not knowing what car you have, I can't say whether the failure of the stomp test to work is due the DME not supporting it or whether the test is failing because of a bad TPS or burned out CEL bulb. If the car is a 9/87 or later production 325i/is and the CEL illuminates when you switch on the ignition, a failure of the stomp test will be caused by a bad or mis-adjusted TPS. If the CEL doesn't illuminate when the ignition is turned on, replace the bulb and try again.
          So, I cannot hear the fuel pump turn on...

          I installed the cap and rotor the only way possible?!?!

          Also i never unhooked the CPS from the top end, only from the hard bracket at the lower part of the motor and let it dangle. so there is no possible way for me to switch the CPS and the cylinder ID. just for reference. my Cylinder ID (from the front of the car locking towards the back) plug is on the left and my CPS is on the right.

          The car is an 89I, i do not see a check engine when the ignition is turned to on (therefore it is most likely a bad bulb).

          Comment

            #6
            In that case I suspect damage to the wires of the CPS, probably from the plastic retainer on the front of the timing cover being missing and the wire hitting the water pump pulley. The CPS is the only thing in the area where you were working that would result in no spark and no operation of the fuel pump. If you have neither, I'd suggest the CPS as the cause. The other likely possibility would be the main relay, but changing the timing belt should not have disturbed that.
            The car makes it possible, but the driver makes it happen.
            Jim Levie, Huntsville, AL

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              #7
              I did find that the CPs was damaged even though I do have the correct retainting price on the timing cover.

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                #8
                so on a whim i decided to try and start the car... and magically it worked?!?!?! only thing that has changed is that it sat for 24 hours, and was outside in the hot sun. other then that i have done ZERO to the car. So i took the chance to bleed the system and i am sitting at half way on the temp gauge on this super fine hot day.

                only problem now is that my new rears are rubbing and i need to roll my fenders... :( no driving for me today.

                still going to keep the extra CPS wire i ordered just in case...

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