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  • Dave @nz
    replied
    Originally posted by basketcase View Post
    At work if I were just to throw parts at a problem like this I would be out of a job. The test bulbs idea is good but time consuming to setup, and watch. If you fit a jumper wire between 30 and 87 on the relay(s), and then drive the car until it either fails or doesn't, then you have isolated the circuit which is causing the issue. That's the first step in fixing the problem, is isolation.
    Yes I agree and see what you are saying makes a lot of scene bridge pine 87 and 30 of the main relay that really out, with the light idea shows if power supply is getting to the relay via ignition switch and OBC relay.

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  • basketcase
    replied
    At work if I were just to throw parts at a problem like this I would be out of a job. The test bulbs idea is good but time consuming to setup, and watch. If you fit a jumper wire between 30 and 87 on the relay(s), and then drive the car until it either fails or doesn't, then you have isolated the circuit which is causing the issue. That's the first step in fixing the problem, is isolation.

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  • Dave @nz
    replied
    Can you print out the wiring diagrams for the DME in A3, page 1364-4 would be a good place to start. http://wedophones.com/BMWManualsLead.htm

    What may help is connect up 2 test light bulbs inside of the car that you can monitor while driving with thin speaker wires going to terminal 86 of the main computer relay and other bulb connected to terminal 87 of the fuel pump relay.

    The first one will check the power supply through the ignition switch and OBC relay.
    Second will check test power supply out of the fuel pump relay.

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  • RAD2LTR
    replied
    Still the same issue I've been chasing since April. It just has become frequent enough that I've stopped driving the car for the most part. I think I'm now $1400 into new parts for it and the problem is still here, and worse than ever, yet I'm no closer to fixing it. I know its something insanely off the wall and stupid, but I don't have the slightest idea what it might be now.

    Will

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  • irdave
    replied
    Is this a different problem? I mean, did you solve the first problem only to uncover another?

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  • basketcase
    commented on 's reply
    You can test the circuit with an ohmmeter for resistance (set your multimeter to ohms) and with each wire isolated from the circuit you should read only a few ohms max. Ideally 1 ohm, but 2 or 3 is acceptable for a longer line. But that does not test the circuit under load. To do that you need to do a voltage drop test. Not easy for a relay circuit. Actually ohms testing a relay circuit is not fun either. Bridging the relay is the first step IMO to see if that stops the problem.

    A hot coil is fine when engine is running. All cars run with a hot coil when driving. Just disconnect the wire you fitted when you are parking it up. Really that's what I would be doing if this were my car.

    Make sure you fit the 12v feed to the 12+ side, not the ground side. The 12+ side is coming from ignition switch.

  • RAD2LTR
    replied
    Originally posted by basketcase View Post
    Yes as the relays all have been replaced it might be a wiring issue. Each relay has a control side and a load side. If the wiring on the control side gets a high resistance, it could de-energise the relay. I'm not saying its the ignition switch yet. I think as you are getting this fault regularly now, it is time to isolate the circuit causing the problem. Then narrow down the fault in that circuit whether it is a wiring or component issue.

    Yes the coil will be hot at all times. This is only for testing purposes, so just disconnect the wire once you are satisfied the feed to the coil is either at fault or not. After driving the car just pop the hood and disconnect.

    If that does not make a difference, then try bridging the load side of the relays one at a time, pins 30 and 87. That takes the control side of the relay out of the equation (86 and 85) . If the fault stops by doing this to one of the relays you can then diagnose that circuit.

    These are all temporary measures for diagnosis obviously. The cars battery will drain pretty quickly if left on, and risk of burning out a component.
    If a high resistance is causing a relay to kick off, wouldn't I be able to test that with a voltmeter? If so, how many ohms should I see? I have to say running around with a hot coil for an unspecified amount of time doesn't sound like fun. Yes, the issue has been more regular, but I can't say it will show in one drive or in 20.

    Will

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  • basketcase
    replied
    Yes as the relays all have been replaced it might be a wiring issue. Each relay has a control side and a load side. If the wiring on the control side gets a high resistance, it could de-energise the relay. I'm not saying its the ignition switch yet. I think as you are getting this fault regularly now, it is time to isolate the circuit causing the problem. Then narrow down the fault in that circuit whether it is a wiring or component issue.

    Yes the coil will be hot at all times. This is only for testing purposes, so just disconnect the wire once you are satisfied the feed to the coil is either at fault or not. After driving the car just pop the hood and disconnect.

    If that does not make a difference, then try bridging the load side of the relays one at a time, pins 30 and 87. That takes the control side of the relay out of the equation (86 and 85) . If the fault stops by doing this to one of the relays you can then diagnose that circuit.

    These are all temporary measures for diagnosis obviously. The cars battery will drain pretty quickly if left on, and risk of burning out a component.

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  • RAD2LTR
    replied
    Originally posted by basketcase View Post
    To me that sounds like a relay de-energising causing the EFI to kill the car, and once you cycle the key the relay gets a fresh voltage and starts.

    As this is starting to happen regularly that is a good thing. Easier to diagnose.

    To check if the ignition switch is failing and dropping out spark via the coil, run a 12v feed to the coil straight from the battery main feed. Drive the car and if no more cut outs then trace the 12v from coil to ig switch find the fault.

    If it keeps happening then maybe DME relay, wiring, fuel pump relay or wiring

    Bridge each relay one at a time to see what stops the cutting out
    The relays have all be replaced, so I'm pretty sure its not a relay. That said, it could be a relay being de-energized and re-energized when I turn it off and back on. This would point to the ignition switch wouldn't it?

    If I run a wire directly from the main power block behind the coolant tank down to the coil, that would leave the coil hot all the time wouldn't it? How would I turn the engine off with a hot coil short of standing on the brakes and letting the clutch out?

    Will

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  • basketcase
    replied
    To me that sounds like a relay de-energising causing the EFI to kill the car, and once you cycle the key the relay gets a fresh voltage and starts.

    As this is starting to happen regularly that is a good thing. Easier to diagnose.

    To check if the ignition switch is failing and dropping out spark via the coil, run a 12v feed to the coil straight from the battery main feed. Drive the car and if no more cut outs then trace the 12v from coil to ig switch find the fault.

    If it keeps happening then maybe DME relay, wiring, fuel pump relay or wiring

    Bridge each relay one at a time to see what stops the cutting out

    Leave a comment:


  • RAD2LTR
    replied
    So I threw my spare AFM in because it was there and I'm grasping for anything at this point. Wasn't the AFM. It cut on me twice about 5 min into a drive. I didn't bother pulling over, just clutch in turned it off and restarted. Started instantly. The second time it cut and died, I just turned it from run to off back to run and the engine restarted the second the key made it back to the run position. Could it be a bad ignition switch?

    Will

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  • RAD2LTR
    replied
    Originally posted by rewilfert View Post
    I didn't read through this whole thread carefully, but have you replaced the main relay (behind the coolant tank)? My car started dying on a road trip this past summer and I was able to trace the issue to the main relay.
    That was one of the first things I replaced. Then the pulse generators, fuel pumps, ECU, spark plugs, wires, cap & rotor, coil, water temp sensor, cleaned every ground on the car,

    Will

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  • rewilfert
    replied
    I didn't read through this whole thread carefully, but have you replaced the main relay (behind the coolant tank)? My car started dying on a road trip this past summer and I was able to trace the issue to the main relay.

    Leave a comment:


  • RAD2LTR
    replied
    Originally posted by Dave @nz View Post
    Hi Will,
    Can you borrow a fuel pressure gauge and connect it up to see what the fuel pressure is doing when it dies, on the up shot now it is happening all the time it will be much easier to diagnose.
    If the ignition switch was faulty the RPM needle would drop quickly, not sure if that is happening in you case.
    There is a OBC relay under the dash drivers side which supplies or cuts power to the DME when the code is installed, just wondering if it could be related to your problem.
    Dave
    How exactly do I check the fuel pressure when it dies, since I never know when it will die? ( I guess I could put my DME back in and stand there and watch, hoping it decides to die. I don't know if that would be a valid test since I know there is an issue with that DME that is different from what is going on with the loaner one.) I have a fuel pressure tester that I could hook in and watch, but I don't know if that would tell me much since it might not do its thing at idle, and if it does, did it die because of the known bad DME, or to the issue that causes the cut with the known good DME (The loaner is a rebuilt one from Programa with a Conforti chip in it.)

    The tach needle falls with engine rpm when the engine cuts (Goes to zero with the clutch in if I'm driving, comes back up if I let the clutch out.)

    I've considered the OBC relay, however I was told by Bill Arnold that if the relay has issues it won't restart. Its totally dead. This was one of my first thoughts, but it sounds like the odds of this being the culprit are pretty low.

    Could it possibly be an issue with the alternator doing something strange? My dad had a Jaguar XJR that would randomly cut out and the issue turned out to be the alternator. (I'm guessing the odds of this being the issue are very low.)

    Will

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  • Dave @nz
    replied
    Hi Will,
    Can you borrow a fuel pressure gauge and connect it up to see what the fuel pressure is doing when it dies, on the up shot now it is happening all the time it will be much easier to diagnose.
    If the ignition switch was faulty the RPM needle would drop quickly, not sure if that is happening in you case.
    There is a OBC relay under the dash drivers side which supplies or cuts power to the DME when the code is installed, just wondering if it could be related to your problem.
    Dave

    Leave a comment:

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