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No start question - CPS

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    #1

    No start question - CPS

    Dropped the motor back in the 325is I picked up for free this weekend. Having a no start issue.

    Did some research and noted some have had the crank position sensor plug mixed up with the spark plug impulse sensor.

    My question is, the connectors come off the harness in the same location, the plugs are identical and the wire colors appear the same.. How do I know which one is for the CPS and which one is for the Spark plug wire sensor?

    The car is getting fuel to the rail, has spark and will fire up for a second with starting fluid. Plugs are dry when pulled so it seems to be no firing of the injectors is the issue.

    Also worth noting is we don't have the exhaust on yet so no o2 sensor but I don't think that matters for start permissive?
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    #2


    There's only one way that the wires really "fit." Old wire especially should be formed to fit in only one comfortable way. One of the first things I do is put a bit of white electrical tape around the cps wires, both sides. Makes it easier.

    I've run an e30 without an exhaust. It's loud. Hahah.

    Do you have the gas in and return lines mixed up? That's another common mix up. If it starts with starting fluid I would say your CPS is plugged in correctly. It wouldn't spark otherwise.
    AWD > RWD

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      #3
      You say it wouldn't spark otherwise? Is that correct? I would think if there is power to coil and distributor is hooked up there would be spark, spark timing is based on distributor reference not ECU but I could be wrong.

      I picked up the car without the motor in it and unfortunately none of the connections were labeled.

      So is there some other way to determine which is the correct one? I know I can just switch them and see what happens, but it makes it difficult to determine the real problem if it is not this wiring cause I'll have many more combinations of things to try.. I'd rather just know this is correct then move on to the next thing..

      Comment

        #4
        You could get a volt meter and ohm the cps pins at the computer to the cps connector to find the right one. Maybe cut back the rubber boot or harness to find the color of wires and match them to the electronic manual. Also on eta models there is a white plastic ring( zip tie looking) on the harness side of the engine speed sensor connector to help tell them apart. Maybe bmw did the same with the I engine. I would put a zip tie on the cps in the future to stop the confusion because this seems to be a common problem.

        Comment

          #5
          The cps needs to be plugged in for the computer to see timing. Without seeing timing data, there will be no spark. Also, spark timing is based off the harmonic balancer that the cps reads, not the distributor.

          Double check your fuel lines...
          AWD > RWD

          Comment

            #6
            the easiest way is to just switch the two plugs and see what happens. pull a plug and check for spark. check your relays too.

            sounds like a simple mixup

            Comment

              #7
              If you're getting spark then the CPS is connected up correctly, if you have fuel pressure at the rail then it can only be fuel metering - a noid light will tell you if the injectors are firing.

              Does this car have the dreaded C191 connector ? The round plug & socket under the intake manifold.

              Comment

                #8
                Yes, it does have the round plug under the intake manifold. Should I clean the connections to make sure it has good conductivity?

                I'll be trouble shooting on the car tonight. Will verify spark and if we have then assume the CPS is correct and then move down the list.

                The fuel lines are correct, good pressure at the rail.

                So, no o2 sensor should not be an issue? It will have one once the exhaust is built but just trying to see if it runs now.

                I have also read ICV could be an issue?

                Car def also has some vacuum leaks thru air boot, it's cracked from sitting for so long, just waiting on a new intake boot to come in.

                Here is a pic of the car for fun. For those that haven't seen my other post I picked this up for free, I was picking it up as a 'parts car' but have decided to get it running and send it to a new home. 104k original miles, rust free tx car, zero accidents, original paint.



                Comment

                  #9
                  ICV, O2 sensor, temp sensor - all can cause running problems but the car should start or at least try if you have compression, fuel and spark.

                  I'd check out that C191. Very carefully pull back the rubber covers and check that you have continuity from the wire going into the plug and socket -then check continuity across the plug assembly. Make sure it's fully screwed together.

                  You should have 12v on the white/red wire - that is the common injector power.

                  If you have any wire adrift (brown/white or brown/yellow) then the injectors aren't getting a ground from the DME.

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