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Ignition Coil 1 (1271) - What's next?

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    Ignition Coil 1 (1271) - What's next?

    My check engine light has not been on, but I decided to perform a stomp test in an effort to diagnose a separate issue (thermostat stuck open). I was surprised to see the stomp test revealed code 1271: Ignition Coil 1.

    The car has been running smoothly. No noticeably misfires at any RPM. Aside from my coolant temps being lower than normal (likely due to thermostat stuck open) the car has been running well. 137K miles. Within the last 1,000 miles I've replaced the mess under the intake with all OEM parts (hoses, clamps, gaskets, injectors).

    To further diagnose the issue I have done the following:

    - I swapped plug wire 1 and 3. Reset codes. Verified codes cleared. Started engine. Stopped engine. Checked codes again to reveal 1271.
    - I swapped spark plugs. Reset codes. Verified codes cleared. Started engine. Stopped engine. Checked codes again to reveal 1271.
    - I swapped coil 1 and 2. Reset codes. Verified codes cleared. Started engine. Stopped engine. Checked codes again to reveal 1271.
    - The plugs all look normal.

    Any ideas what could be causing this code every time I start the car? Based on the tests above, I would've expected the code to change to a different coil/cylinder based on swapping plug wires, plugs, and coils. That had no effect and it was coil 1 each time.

    #2
    I vote ecu, at this point. It's the constant in your equation.

    My experience with the 'diagnostics' on these ecus is that they're spotty at best.
    I was shocked when the MS43 in the E46 properly self- diagnosed...

    I'd run it until it misbehaves- as in, the car runs poorly. If it ever gives trouble,
    do the same thing you've done to troubleshoot it this time- and then swap the ecu.

    t
    now, sometimes I just mess with people. It's more entertaining that way. george graves

    Comment


      #3
      Originally posted by TobyB View Post
      I vote ecu, at this point. It's the constant in your equation.

      My experience with the 'diagnostics' on these ecus is that they're spotty at best.
      I was shocked when the MS43 in the E46 properly self- diagnosed...

      I'd run it until it misbehaves- as in, the car runs poorly. If it ever gives trouble,
      do the same thing you've done to troubleshoot it this time- and then swap the ecu.

      t
      Thanks. I'm looking into buying a spare ECU/DME now.

      Comment


        #4
        The transistor for coil one might be going out. Pull the cover off the ECU and look for burning. It's fairly common on M42 cars.

        Comment


          #5
          Originally posted by AndrewBird View Post
          The transistor for coil one might be going out. Pull the cover off the ECU and look for burning. It's fairly common on M42 cars.
          Thanks! I'll try to find some time for that this weekend and report back. I may have found a local DME as well.

          Comment


            #6
            I'm trying to diagnose my issue with has this code and sputtering/misfire randomly. Did you ever figure it out?

            Comment


              #7
              Originally posted by CTDRIVER86 View Post
              I'm trying to diagnose my issue with has this code and sputtering/misfire randomly. Did you ever figure it out?
              I never did figure this out. And I haven't checked codes in a long time. I'll do a stomp test this evening and see if the code is still there. I've since swapped coils, plugs, ECU (spare with chip), and a number of other items just a general refresh/update, so I'm curious to see if it still throws/stores that code.

              Comment


                #8
                [nerd content warning]
                Some (not all) Motronic 1.7 variants used in our cars have ignition coil fault detection circuitry. Only later versions seem to have it. Basically, when the ECU wants to charge a coil, one of four high current transistors connects the primary winding to ground (the other side is at 12V from the ignition switch). It charges for the specified dwell time, usually ~4ms, and then shuts off the transistor at the crank angle where the spark is desired. This makes the spark, but it also produces a VERY high inductive flyback voltage on the wire between the coil and ECU. The transistors have internal circuitry to clamp this flyback to ~450V. This high voltage spike is what is used for fault detection. All 4 coil primary lines on the PCB have branches that route to a daughter-board where the voltage is divided down to <5V by resistors, and then compared to a reference voltage in a comparator. If the flyback voltage is high enough (IIRC, >120V) it will trigger the comparator output. The microcontroller in the ECU will check to see if the comparator output has triggered after firing each ignition coil. If it is not triggered, it means that the coil primary was not able to draw enough current to produce a sufficient flyback voltage, either because it burned up and went open circuit, the connector/wiring went bad or the driver transistor took a dump. It can NOT determine an issue with the secondary winding, plug wires or spark plug.


                Anyway, I have heard of a few rare cases where the driver transistor went bad in the ECU. They are incredibly robust devices, and the only way I can see them failing is if there is water damage in the ECU, a big short on the coil control line such that it connects directly to 12V (rather than through the ignition coil) or some sort of major over-temperature condition in the glove compartment.

                If the code sticks to coil #1, even after swapping coils around, then maybe there is an issue with the transistor, or the fault detection components, or the wiring. Spare ECUs are cheap on eBay and probably worth a shot.

                Transaction Feedback: LINK

                Comment


                  #9
                  Originally posted by bmwman91 View Post
                  [nerd content warning]
                  Some (not all) Motronic 1.7 variants used in our cars have ignition coil fault detection circuitry. Only later versions seem to have it. Basically, when the ECU wants to charge a coil, one of four high current transistors connects the primary winding to ground (the other side is at 12V from the ignition switch). It charges for the specified dwell time, usually ~4ms, and then shuts off the transistor at the crank angle where the spark is desired. This makes the spark, but it also produces a VERY high inductive flyback voltage on the wire between the coil and ECU. The transistors have internal circuitry to clamp this flyback to ~450V. This high voltage spike is what is used for fault detection. All 4 coil primary lines on the PCB have branches that route to a daughter-board where the voltage is divided down to <5V by resistors, and then compared to a reference voltage in a comparator. If the flyback voltage is high enough (IIRC, >120V) it will trigger the comparator output. The microcontroller in the ECU will check to see if the comparator output has triggered after firing each ignition coil. If it is not triggered, it means that the coil primary was not able to draw enough current to produce a sufficient flyback voltage, either because it burned up and went open circuit, the connector/wiring went bad or the driver transistor took a dump. It can NOT determine an issue with the secondary winding, plug wires or spark plug.


                  Anyway, I have heard of a few rare cases where the driver transistor went bad in the ECU. They are incredibly robust devices, and the only way I can see them failing is if there is water damage in the ECU, a big short on the coil control line such that it connects directly to 12V (rather than through the ignition coil) or some sort of major over-temperature condition in the glove compartment.

                  If the code sticks to coil #1, even after swapping coils around, then maybe there is an issue with the transistor, or the fault detection components, or the wiring. Spare ECUs are cheap on eBay and probably worth a shot.
                  Good info, my CEL has been coming on intermittently but has been fine for thousands of miles. Stomp test reads 1271. I haven't swapped coils (COP swap) due to the modified #1 coil, but was going to swap and see if the issue was isolated to the coil or not. If it is not, this is good info and I can swap ECU's to test the problem.
                  318iS Track Rat :nice: www.drive4corners.com
                  '86 325iX 3.1 Stroker Turbo '86 S38B36 325

                  No one makes this car anymore. The government won't allow them, normal people won't buy them. So it's up to us: the freaks, the weirdos, the informed. To buy them, to appreciate them, and most importantly, to drive them.

                  Comment


                    #10
                    Just an update: I figured it out. The Fuel pump worked but had low pressure. After replacing the fuel pump with TRE unit. Car is running better than it has ever been

                    Comment


                      #11
                      I've had a TRE pump in my parts shelf for a while. Wonder if I'll notice a difference. Engine runs smooth already, but I'd like a little extra pep.

                      Comment


                        #12
                        Originally posted by mike.bmw View Post
                        I've had a TRE pump in my parts shelf for a while. Wonder if I'll notice a difference. Engine runs smooth already, but I'd like a little extra pep.
                        Time to turbo it, Mike! :)
                        Steve • Toronto
                        1991 318is • Brillantrot
                        Build Thread

                        Comment


                          #13
                          Originally posted by Powling View Post

                          Time to turbo it, Mike! :)
                          Haha, that would be something.

                          Comment


                            #14
                            Originally posted by CTDRIVER86 View Post
                            I'm trying to diagnose my issue with has this code and sputtering/misfire randomly. Did you ever figure it out?
                            Weird, I am trying to think of how a failing fuel pump would trigger an ignition coil fault. As noted above, I have seen two variants of the M1.7: one with dedicated coil fault detection circuitry, and one without. I wonder if the ones without it try to measure crank speed acceleration to determine if there are misfires on a given cylinder (looks for crank speed increase after firing the ignition)? I know that this sort of functionality was standard in later Motronic and Siemens ECUs, but I don't think that it was implemented in M1.x. Then again, the fault reporting in M1.x is super goofy and seems to report the wrong source of problems more often than it gets them right!

                            By any chance, could you pop the cover off of your Motronic and post a photo of the top-side of the PCB? I am super curious now!

                            Transaction Feedback: LINK

                            Comment


                              #15
                              k
                              Originally posted by bmwman91 View Post

                              Weird, I am trying to think of how a failing fuel pump would trigger an ignition coil fault. As noted above, I have seen two variants of the M1.7: one with dedicated coil fault detection circuitry, and one without. I wonder if the ones without it try to measure crank speed acceleration to determine if there are misfires on a given cylinder (looks for crank speed increase after firing the ignition)? I know that this sort of functionality was standard in later Motronic and Siemens ECUs, but I don't think that it was implemented in M1.x. Then again, the fault reporting in M1.x is super goofy and seems to report the wrong source of problems more often than it gets them right!

                              By any chance, could you pop the cover off of your Motronic and post a photo of the top-side of the PCB? I am super curious now!
                              Well I checked for spark and it was normal. When I checked the fuel pump, it looked normal at first but then realized it was running low pressure. Once I changed the pump, the car fired right up and has been running fine ever since. I don't know if I feel more pep but the car does idle smoother and has smoother pickup throughout the rev range.

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