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no start (have fuel, spark, + injectors getting 2v with ignition??)

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  • #16
    I can confirm your test method but it doesn't prove the Relais is actually switching. To confirm that you must check whether terminal 87 carries 12V when cranking.
    If you get spark when cranking your tdc (=crank) sensor and your engine speed sensor next to it are working fine.
    Check for solid, zero resistance earth connections:
    Bolt at the corner of the lower oil pan to left chassis rail (below air filter housing) and the other connects the tray where the expansion tank sits to a bolt at the rear the cam carrier cover.

    You identified 14 and 15 that pull the injectors to ground in order to spray.
    Check the wiring loom between the injector connectors of injector 1&2 and pin14 and 3&4 and pin15 inside the dme plug with a Multimeter set to measure resistance/continuity. the loom passes the test when you measure 0.0x Ohm or continuity (beep).


    Make sure that both terminals 87 at the DME relais carry 12V when ignition is on AND also when cranking.
    The thick red/white wire connects this terminal 87 to all 4 injectors and provides them 12V.

    Engine wiring schematics as an alternative to the ETM:
    http://www.s14.ctmnet.de/0053/0053_11.htm
    and
    http://www.s14.ctmnet.de/0053/0053_12.htm

    Use Google to translate the part descriptions
    Rt=red ge=gelb=yellow, sw=schwarz=black the other abbreviations are identical to the ones used in ETM.

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    • #17
      hardtailer thanks for confirming tdc crank speed sensors working with spark.

      Will check grounds and re-check the dme relay and report back!

      Appreciate all the help!

      Comment


      • #18
        hardtailer I have verified continuity at the two engine ground locations you suggested, they test and look good.

        back probing main dme relay and second meter terminal at a ground location:

        Terminal 87 (middle one):
        - key out 0v
        - key at ignition 12v
        - key cranking 12v

        Terminal 87 (exterior):
        - key out 12v hot
        - key at ignition 12v
        - key cranking 11v

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        • #19
          Pulled computer/ecu, probed pins 14 & 15 using an analog ohm meter both pins shoot the needle to half of the full continuity on all left-side injector pins.

          Doesn't matter if probing pin 14 or 15, i get the same reading across all injectors.

          Side note: tried swapping ecu with a spare but didnt change the reading. No 12v at injector harness when cranking; more like a steady 2v-ish

          Seems like there's a short in the injector harness somewhere, agreed? Where's the best place to start looking?

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          • #20
            I'm researching the c191 connector for the injector harness, it's under the intake and sometimes gets corroded by a coolant leak from the throttle body warmer...

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            • #21
              The resistance measurement results indicate that you have a resistance of a value 'half the scale' in the wiring loom and or connector c191.
              This resistance reduces the 12V down to 2V at the injectors.
              The two splices (14 to left terminal of inj 1 and inj 2 and 15 to 3&4) are within the plastic injector connector housing. On page 1364-5 of the 1987 M3 ETM they're shown as S104 and S106.
              Another high resistance /bad connection could be in the engine loom connector next to th fuse box (C101)

              One of your results of the main relay are unexpected:
              Terminal 87 (exterior): key out 12v hot --> this should be zero Volt , like the middle one.
              (perhaps you accidentally measured terminal 30?)

              Disregarding this for a moment, check wat voltage you measure at each right terminal of each and every injector using the same (or another known-to-be good) ground with ignition on and while cranking.
              What do you get?

              If 11-12V you're good, wiring and connections are fine on the +12v side of the injectors.
              If anything less than battery voltage (0-10v) then look into the same connectors as on the negative side and the splice inside the plastic housing (splice 112)

              Tell us your fidings please!

              Comment


              • #22
                Originally posted by BMWi4 View Post
                I'm researching the c191 connector for the injector harness, it's under the intake and sometimes gets corroded by a coolant leak from the throttle body warmer...
                there is no throttle body warmer on the M3.

                T

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                • #23
                  Originally posted by HANDBLT View Post

                  there is no throttle body warmer on the M3.

                  T
                  This was dumb on my part, I was reading a post about an m20... no tb warmer on the m3.

                  Comment


                  • #24
                    Originally posted by hardtailer View Post
                    The resistance measurement results indicate that you have a resistance of a value 'half the scale' in the wiring loom and or connector c191.
                    This resistance reduces the 12V down to 2V at the injectors.
                    The two splices (14 to left terminal of inj 1 and inj 2 and 15 to 3&4) are within the plastic injector connector housing. On page 1364-5 of the 1987 M3 ETM they're shown as S104 and S106.
                    Another high resistance /bad connection could be in the engine loom connector next to th fuse box (C101)

                    One of your results of the main relay are unexpected:
                    Terminal 87 (exterior): key out 12v hot --> this should be zero Volt , like the middle one.
                    (perhaps you accidentally measured terminal 30?)

                    Disregarding this for a moment, check wat voltage you measure at each right terminal of each and every injector using the same (or another known-to-be good) ground with ignition on and while cranking.
                    What do you get?

                    If 11-12V you're good, wiring and connections are fine on the +12v side of the injectors.
                    If anything less than battery voltage (0-10v) then look into the same connectors as on the negative side and the splice inside the plastic housing (splice 112)

                    Tell us your fidings please!
                    Picked up the refurbished and cleaned injectors, they are now confirmed working.

                    Will check and report back; thank you for your help in this!

                    Comment


                    • #25
                      Computer about to die so I'm just going to put this here, scary how similar the symptoms are: https://s14net.vbulletin.net/forum/s...jector-problem

                      Almost sounds like the same problem, I haven't had the time to troubleshoot but will be back at it this wekeend! Can wait to report back

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                      • #26
                        Any updates?

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                        • #27
                          Had a little time to look at it ther other day, swapped the cylinder identifier tdc and speed sensor with known good sensors to rule them out. No change.

                          Did a test and ohmed the ecu plug pins to verify they were correctly plugged in the right sensors. Ecu pins 8&27 go to the engine speed sensor and 25&26 go to the cylinder identifier; for some reason my red zip tie fell off the engine speed sensor (upper of 2 sensors).

                          Also, as a side note, can confirm that if these sensors go bad, you will not get spark.

                          I'm going to look at the etm and test the splices, injectors and take a look at c101. Last time I opened c101 it seemed clean (corrosion free).

                          Thank you gord following up, I will do the testing you recommended and post the results

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                          • #28
                            Something was wrong with my $1 sears meter or the leads weren't getting a good connection so purchased a new multi-meter to troubleshoot and found that on cranking, there is 11v getting to injectors and about 7.4% duty cycle. Injectors seem fine, I also listened to them with a stethoscope.

                            **Fuel pressure regulator not building pressure**

                            Thanks again to everyone who helped, especially Dave@nz hardtailer 808M nilsp ttw18 I was chasing the wrong thing because of an incorrect test.

                            Comment


                            • robb
                              robb commented
                              Editing a comment
                              I am two threads below you with an extremely similar issue....so it turned out to be your FPR? Did you use a fuel pressure gauge to verify this? If so what pressure should you be reading? This will be my next step for sure. Oddly with my issue my pumps do not prime at all when turning the key but will all turn on when jumping the FP relay? Thanks for the read this helped me go through similar steps!

                          • #29
                            Remove your fuel and jump the pins 87 and 30 with a paperclip, do you hear the fuel swishing through the rail? Pumps probably good if yes, or atleast one of them works

                            Use a meter to ohm the fuel relay, apply 12v is does this close the circuit? (this test doesn't necessarily tell you if the relay is good but may uncover a bad relay)

                            Comment


                            • robb
                              robb commented
                              Editing a comment
                              Thank you and yes, I can jumper the FP relay at those pins and they all turn on string and I can hear the fuel running through the lines. FP relay is new and volt meter confirmed it was good also. Just strange the pumps will not prime when I go to crank it over?

                          • #30
                            This is a 3bar fuel system.

                            Have you tried starting the car with the relay jumped?

                            Comment


                            • robb
                              robb commented
                              Editing a comment
                              Yes, I jumpered the relay and still it will not start even with the pumps all singing to me?! I am checking the fuel pressure and also voltage at the injector rail pins to see what the voltage is. Did your M3 go through a similar issues as this or was it purely just the pressure was not enough to your injectors? I may pick up a new FPR this weekend as well just in case... thanks for your thread by the way- it helped me take similar steps to diagnose I am just not at a running engine yet so I appreciate it!
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