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  • #16
    This might be helpful to other people, I searched some old threads here and found the following info about the two pulse sensors:

    The lower (nearer to the ground) sensor is for cylinder identification, this tells the DME which cylinder is firing by reading crank position. I guessing this is the one which will prevent your car from starting if it breaks. No signal from this sensor and the DME probably won't give spark and/or fuel.

    The upper sensor is for sensing engine speed and tells the DME how fast your engine is turning. From my experience, the car will still start and run if this sensor is not working but the DME might not know how fast your engine is turning. I have no factual basis but running with this sensor not working may cause problems. For one thing, I'm guessing the rev limiter may not work and you could potentially over rev your engine.

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    • #17
      Sorry I got things a bit mixed up, correction, it is the engine speed sensor (the upper one) that will prevent your car from starting if it is defective.

      With the cylinder identification sensor (lower one) defective, the engine will still start and run. I'm not sure what the consequences of driving your car with this sensor not working properly, but I personally would not do it.

      HTH.

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      • #18
        Thread revival...

        For about a month I've had random instances of the engine cutting out (usually at inopportune times like merging onto the freeway). Its like someone shut the electrical off to the engine alone, and then it comes back a couple seconds later. Yesterday it did it once, and this morning it did it 3 times in 11 miles, but didn't do it on my drive home from work. Is this indicative of the flywheel sensors going bad? I've checked all the grounds and they look good. The plug wires are about 8 years old, but look to be in good shape (Moroso wires from VAC.) I don't think its a fuel related issue since it doesn't act like its out of fuel, but it does act like someone chopped the ignition, but then it comes back. It was doing it on fresh smooth asphalt today.

        Awhile back I had a main relay issue where the engine would fully die, so I replace the relay, but this isn't fully dying, just cutting and recovering. Any thoughts?

        Thanks,
        Will
        '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
        '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
        '88 M3

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        • #19
          Hi Will,
          I donít know about flywheel sensors what their failure mode is other than no starting.
          Worth removing the lid on the AFM and checking for worn through track.

          If your M3 is the early type it should have two fuel pumps you can run some jumper wires from a battery to individually power up each pump to test that you infect have two operational pumps incase one has died and the other is on its way out.

          I think I would check the inline fuse near the + battery terminal then removing the DME for inspecting the solder joints next.
          Dave

          E30 M3 1987
          Mini Clubman GT
          BMW E36 323 Msport
          Toyota Corona
          KTM 200EXC
          Honda CB50 (1979)

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          • #20
            Originally posted by Dave @nz View Post
            Hi Will,
            I donít know about flywheel sensors what their failure mode is other than no starting.
            Worth removing the lid on the AFM and checking for worn through track.

            If your M3 is the early type it should have two fuel pumps you can run some jumper wires from a battery to individually power up each pump to test that you infect have two operational pumps incase one has died and the other is on its way out.

            I think I would check the inline fuse near the + battery terminal then removing the DME for inspecting the solder joints next.
            Dave
            I do have two pumps, and they are both relatively new. I also replaced the AFM a few years back, so I don't think that is the issue (I do have the old one in a box somewhere that I could use as a test however.) I did have a look at the inline fuse and it appears to be ok.

            Thanks,
            Will
            '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
            '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
            '88 M3

            Comment


            • #21
              It does sound like an intermittent grounding issue. You checked the ground cables to the block, the one in the trunk for the battery, and the ground pin that's next to the DME above the glove box? Does the dash/radio/clock go out when the car dies?

              It could also be an intermittent fault within the DME but I'd start by looking into the more obvious causes first, unless you have a spare DME to try.
              Last edited by Mick; 07-09-2019, 08:21 AM.

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              • #22
                I checked all the ground cables and they are all good, including the one next to the DME. The dash/radio/clock are unaffected. It was fine on my drive home yesterday, and on my way to work today. I don't have a spare DME to swap in, I wish I did. I ordered a new set of plug wires yesterday, I'll get them installed as soon as they arrive. I checked the leads to the coil and they are all tight.

                Will
                '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
                '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
                '88 M3

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                • #23
                  I had solder break on the circuit board of the ecu. Something like that could cause intermittent cutting out.

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                  • #24
                    Have you tried replacing the fuel pump relay? It caused me some intermittent stalling problems.

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                    • #25
                      I had the same thing, it was a bad connection in the ECU to pin#1 which tells the coil when to fire. If you can remove the black cover in the glovebox, so you can push up and down on the ECU connector while it's running, mine would cut out. This is how I found it.

                      T

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                      • #26
                        Well, I replaced the plug wires and the coil. The plug wires had 80-90K miles on them so it was time. The issue was back last night. The car was fine while driving over to a friends place, when I came home about 10 pm. I got about a mile down the road and the sputtering and hacking was back. It misfired and was generally unhappy for about another mile, and then cleared up. The car never fully died, just sputtered and hesitated, sometimes for several seconds. Got home, parked the car in the garage. Got in the car this morning, it started right up, and headed off to do my errands. Water temp gauge was showing just past the 1/4 mark, oil temp was just reading above 120. The car started hacking and sputtering again. It bucked and snorted for about 8 miles and cleared up and was fine the rest of the day. I put about 60 miles on the car and aside from this morning, it was totally fine. I have a new main and fuel relay on order, I'll replace them when they show up later this week. I replaced the main relay about 5 years ago due to the car cutting out and totally dying, but restarting. This is different, it doesn't really fully die, heck, the tach doesn't even drop when it cuts out now. With the main relay when the engine died, the tach did as well. I'm not sure this is the same deal.

                        Will
                        '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
                        '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
                        '88 M3

                        Comment


                        • #27
                          I agree if the engine isn't fully stopped when your incident occurs, it's probably not the fuel pump relay. Could it be too much oxidation on the barometric pressure sensor or the coolant temperature sensor contacts raising the resistance and causing the engine to run too rich and want to stall? Once my fog light didn't come on when I pressed the switch. I checked the bulb and didn't get continuity despite the fact I could see the filament was unbroken. A little bit of sandpaper on the contacts, and voila problem solved.

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                          • #28
                            Originally posted by RAD2LTR View Post
                            Well, I replaced the plug wires and the coil. The plug wires had 80-90K miles on them so it was time. The issue was back last night. The car was fine while driving over to a friends place, when I came home about 10 pm. I got about a mile down the road and the sputtering and hacking was back. It misfired and was generally unhappy for about another mile, and then cleared up. The car never fully died, just sputtered and hesitated, sometimes for several seconds. Got home, parked the car in the garage. Got in the car this morning, it started right up, and headed off to do my errands. Water temp gauge was showing just past the 1/4 mark, oil temp was just reading above 120. The car started hacking and sputtering again. It bucked and snorted for about 8 miles and cleared up and was fine the rest of the day. I put about 60 miles on the car and aside from this morning, it was totally fine. I have a new main and fuel relay on order, I'll replace them when they show up later this week. I replaced the main relay about 5 years ago due to the car cutting out and totally dying, but restarting. This is different, it doesn't really fully die, heck, the tach doesn't even drop when it cuts out now. With the main relay when the engine died, the tach did as well. I'm not sure this is the same deal.

                            Will
                            Itís funny you mention the exact issues I am having with mine right now. My car does not get driven often, and in the spring my daily died, so I started taking it out more. In tank Fuel pump died, installed a new one and it ran better than ever before (Iíve owned it for 3.5 years). Then the problems started. Sputtering, dropping idle, pig rich under full load with misfires. So I replaced the injectors (mine were original and long overdue.) The problem is still persisting. Since I bought the car I have replaced virtually everything fuel and spark delivery related. Spark is there fuel is there. Now it does not want to start at all. Cranks but wonít turn over. Trying the fuel pump relay and throttle position sensor to see if that helps.

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                            • #29
                              For a year or two my E30 325i touring would splutter and go super rich, and then clear itself up. One time I had it happen to me I had the cover off the AFM, and saw that the flap had jammed open! So basically the AFM was telling the dme there was load when there was no load, and DME was sending out fuel to meet the imaginary load.... I sprayed some wd40 on the AFM flap shaft, and freed it up, and the old M20 never ran better, and never faulted again.

                              Yes the m3 is a different engine, but they both still run the temperamental "Barn door" AFM so make sure you discount this as a possible culprit.

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                              • #30
                                bell housing sensors, cracked trace one the DME board, main relay, loose coil ground wire, bad engine grounds, coolant temp sensor connector missing the little rubber insert so it rattles around and causes issues, loose ground at DME, loose + wiring at main power dist block........the list can go on and on. You have to pick a system, be it electrical, fuel, spark, ground....etc and eliminate them one at a time.

                                T

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