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  • Ignition transistor question

    Hey guys, long time owner and first time poster - this is one for the ECU/igniter transistor gurus I suspect.

    1. I have verified, re-verified and re-re-verified this: I am getting an intermittent ignition pulse from the ECU (which is bone stock)

    2. The result is that the coil is only firing twice, then pausing, then firing twice again - tested with both an oscilloscope as well as an inductive timing light on both the coil lead and each of the individual plug leads.

    3. The test condition is repeatable and identical each time - pulse, pulse, pause, pause, pulse, pulse, pause, pause etc.

    4. Unsurprisingly, I am only getting spark on 2 cylinders - 2 and 4. There is no spark on cylinders 1 and 3.

    5. This appears consistent with the well-known firing order (1-3-4-2) - and suggests that the two pauses in the coil triggering are happening at the same time as cylinders 1 and 3 should be firing. The result is a no-start condition, of course.

    6. Do you think this is a sign of the igniter transistor on its way out? Or something perhaps more sinister (ie. the logic control of the transistor itself) - given that it clearly appears to be switching the transistor, correctly, half of the time.

    Odd one this - appreciate your thoughts in advance!

  • #2
    This IS very odd! You could start by borrowing an ECU from someone and seeing if the car starts. If it exhibits the same symptom, I'd try replacing the flywheel sensor that is sensing engine rotation. It's the one over top of the teeth on the flywheel. I'm thinking it may be intermittent for some reason and the ECU is shutting off for part of the engine revolution? If that does not do it, swap that sensor with the TDC sensor. Perhaps it could not be sensing TDC at all since #1 isn't firing. Let us know how you make out.
    Ron ///Man

    • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
    • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
    • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
    • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
    • '89 M3 M3T / ITR Club Racer
    • '94 Spec E36 - Eh....
    • '09 M3 - Tarmac Terrorist
    • '04 330Xi Sport 6 Speed - Snowmobile
    • '07 530 Xi - Highway Star
    • http://www.imwcarparts.com/e30-m3-parts.htm


    Comment


    • #3
      1. Thanks Ron///Man, it is very odd - I am in Australia so s14s are very light on the ground and not sure I could find a known good ECU to swap (wish I could!)
      2. I had understood previously that if the TDC sensor wasn't good, the ignition wouldn't fire at all - rather than the intermittent firing I'm getting now. I'll definitely check the TDC and RPM sensors for both continuity and signal during cranking to see if there's a breakdown in the signal supplied to the ECU.
      3. I might have to pull apart the ECU and have a peek inside at the joints on the transistor - although, again, it's odd that it will fire perfectly fine on 2 cylinders and then not the other 2.

      Cheers

      Comment


      • #4
        So what I would do then is buy one new crank sensor and install it in one of the two locations on the bell housing and try it, if that does not do it, then switch the new sensor to the other bell housing position. If still no go, then perhaps try to locate a new/rebuilt ECU, or replace the ignitor transistor's, or send the entire ECU to someone who rebuilds them?
        Ron ///Man

        • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
        • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
        • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
        • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
        • '89 M3 M3T / ITR Club Racer
        • '94 Spec E36 - Eh....
        • '09 M3 - Tarmac Terrorist
        • '04 330Xi Sport 6 Speed - Snowmobile
        • '07 530 Xi - Highway Star
        • http://www.imwcarparts.com/e30-m3-parts.htm


        Comment


        • #5
          1. Ron///Man, I'll let you know what happens when I change the sensors, you never know.

          2. I'll also post some pics when I pull the ECU apart so we can all see what's going on....from my understanding of how transistors work, for it to be firing at all (even on 2 cylinders) rather suggests that there isn't anything wrong with the transistor itself - so you may well be onto something with the crank sensors.

          3. If anyone with more experience in transistors can chime in with some comments about whether a transistor can partially work (and if so, whether it would partially work in repeatedly the same way) I'd be very grateful!

          Comment


          • #6
            SOLVED!!!

            As it turns out, even though I had put a set of brand new Bosch X5DC plugs in, two of the plugs for some unknown reason were not firing at all (hence the pauses in the pulses on the coil).

            I pulled all 4 plugs and verified spark / non-spark and as expected cylinders 1 and 3 were not sparking AT ALL.

            A good lesson I suppose - just because you have new plugs doesn't mean they're actually not the source of any problems.

            As it happens I replaced them with some NGK D7EA (which have a 17.5mm shank as opposed to the 17mm of the Bosch) which work perfectly and the s14 is happy again

            Comment


            • #7
              Originally posted by S14inoz View Post
              SOLVED!!!

              As it turns out, even though I had put a set of brand new Bosch X5DC plugs in, two of the plugs for some unknown reason were not firing at all (hence the pauses in the pulses on the coil).

              I pulled all 4 plugs and verified spark / non-spark and as expected cylinders 1 and 3 were not sparking AT ALL.

              A good lesson I suppose - just because you have new plugs doesn't mean they're actually not the source of any problems.

              As it happens I replaced them with some NGK D7EA (which have a 17.5mm shank as opposed to the 17mm of the Bosch) which work perfectly and the s14 is happy again
              How could you tell the plugs were not firing if you were watching the coil signal before the plugs to know that it was pausing between the pulses of the ECU?\

              T

              Comment


              • #8
                Originally posted by S14inoz View Post
                SOLVED!!!

                As it turns out, even though I had put a set of brand new Bosch X5DC plugs in, two of the plugs for some unknown reason were not firing at all (hence the pauses in the pulses on the coil).

                I pulled all 4 plugs and verified spark / non-spark and as expected cylinders 1 and 3 were not sparking AT ALL.

                A good lesson I suppose - just because you have new plugs doesn't mean they're actually not the source of any problems.

                As it happens I replaced them with some NGK D7EA (which have a 17.5mm shank as opposed to the 17mm of the Bosch) which work perfectly and the s14 is happy again
                Were the X5DC's made in India?
                Legitimate question.
                Chris L.

                Spray paint and tire shine doesn't equate to a "restoration!"

                Comment


                • #9
                  HANDBLT I pulled all the plugs and left them hooked up to the wires and gave each plug it's own chassis earth with alligator clamp leads. Cranked and watched each of them fire/not fire. I didn't know it was the plugs originally but before pulling the ECU apart I thought I would check them. As it turns out, lucky find.

                  UNHCLL Yes the X5DCs were made in India -is there something about Indian QC I don't know? Interesting

                  Comment


                  • #10
                    Bosch has moved manufacturing all over the place.
                    If you inspect them closely, you'll find a few issues - The ground electrode, is not parallel to the center electrode. It is also not made with perfect 90* edges/corners, and has variations in the terminal shape where it connects to the plug wires that can cause issues when trying to remove the plug wires (excessive force required, risking tearing the plug wire boot).

                    Conversely, if you buy OE X5DC's from BMW (At a whopping ~$22/ea list price if memory is correct) - they are manufactured in Germany. The ground electrode is perfectly aligned and parallel to the center electrode, and the edges are clean, 90* corners/sides. Additionally, the terminal cap where it connects to the plug wires, is the correct shape to prevent difficulties of removing the plug wires from the top of the plug.

                    -CL
                    Chris L.

                    Spray paint and tire shine doesn't equate to a "restoration!"

                    Comment


                    • #11
                      UNHCLL interesting, I'll check the plugs and take a look for those issues you mention, the NGKs work great although the shank is half a mm too big for the s14 spark plug tool, nothing a little grinding down doesn't fix though.

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