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  1. #1
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    Annual Failure to Thrive Problem

    Guys -
    My '88 325ic has gone on its annual hunger strike, refusing repeated attempts to coax it into starting. Yeah, we've done this before: The first time turned out to be a cracked distributor cap; the next year it was a failed FPR. Geez Tech has been instrumental in locating the previous problems, and I'm hoping he'll pitch in again.
    The fuel pressure is right where it oughta be (~40 psi), the plugs are new and the spark is good (I pulled #2 and left the plug on the valve cover); the position sensor tests out at 507Ω.
    Immediately before the problem developed I'd replaced both the fuel pump and the position sensor for cause; both new units bench-tested fine and are installed correctly.
    Anybody got any ideas? (Please don't tell me it's probably the CPU, because I don't have a spare. Besides, everybody always blames the CPU, and that's never it.)
    Thanks for your help -
    Neil

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    Ray
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    Re: Annual Failure to Thrive Problem

    check the connections in the multi-plug. The signals to fire the injectors flow through there, (and maybe the crank position sensor too). Anyhow, I mean the one on the drivers side, more or less under the throttle plate.

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    Ray
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    link to Alan Alfano's info on this


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    Ray
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    Yes | No

    link to Alan Alfano's info on this


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    Re: Annual Failure to Thrive Problem

    Ray -
    Yeah, I know that puppy - I'll take a look. (And thanks for the url: I'll print it out and save it in my Bentley.)
    Neil

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    Getting REAL close: Somebody get Geez Tech

    I'm back, and I'm closing in on this puppy.
    Running some of the tests in 6.4 of the Bentley gives us this information:
    18 to ground (2 and 36 bridged): Good (~12 volts) (voltage is getting to ECU)
    17 to ground ( " ): Good (injectors click)
    16 to ground ( " ): Good ( " )
    15 to ground (ignition on, no bridge): N/G (no click, zilch)
    14 to ground ( " " ): N/G ( " )
    Now, what the hell does that mean, GT?
    Neil
    PS: In the meantime, while I'm waiting for your call, I'll check the wiring diagrams.
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    Hmm, does the Bentley give you diagnosis tips if the results aren't met? I dont have a ETM here at the house, I will have to check tomorrow and get back to you to see which pins your are jumping and testing.
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    I'm going to need a wiring diagram for the Motronic FI system . . .

    . . . specifically, something that'll show the connection between pins 13 and 14 at the ECU and the injectors. The Bentley doesn't suggest any recourse in the case of N/G conditions for any of the ECU electronic tests, and it doesn't have any useful wiring diagrams, either.
    (According to Alan iX's wonderful treatise on the C191 connector, pins 15 and 16 connect to the injectors through the C191 [and I'm getting correct test results at those pins]. I've got no idea where the wires from 13 and 14 go, though, and those're the ones that are showing a problem.)
    Have you got access to that kind of information, GT?
    Neil
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    Pin 14 at the ECU should be a 2.5mm brown wire and it goes to a grounding point on the right front shock tower.
    Pin 13 is a RXD line for diagnosis by a BMW tester, shouldn't affect starting/running.
    My manual is showing pins 16 and 17 at the ECU to be the ground control for the injectors, not 15 and 16.
    Pin 15 is the ground control for the CEL.
    Is your Bentley for a 3 row DME, not the older 2 row Motronic?
    Did you ever try starting the engine with the fuel pump fuse removed and use just starter fluid?
    “Don't argue with idiots, they'll drag you down to their level and beat you with experience.”

    Find the problem first! Dont spend $$$$$ on parts you may not need.

    Dont be offended if I ask stupid questions, sometimes stupid fixes it.

    '87 325is The best ever
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    Okay: I've got a super-cheap Bosch noid light on order. The price sort of supports my belief that a 12-volt test light will suffice, but now I'll have an honest-to-God "noid light" in my tool box, and when somebody asks, " Have you checked the injectors with a noid light?", I'll be able say Yeah. (Because we all know this stuff is gonna happen again, down the road.)

    But: If this thing really is just a bulb with two leads that plug into the injector connector, can somebody explain why I've got battery voltage at BOTH pins of the connector with the ignition turned on? Aren't the injectors ground-controlled through the ECU? The only way the system could operate with those readings is if one of the wires to each injector carries battery voltage whenever the ignition is on, and the other lead is switched from battery voltage to ground when the ECU wants that injector to fire. That doesn't make much sense to me.
    Neil
    Last edited by dandydog; 04-10-2011 at 07:00 PM.
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    Yes | No
    Just got back but here are some quick observations:
    1) Pin 27: 0 with ignition off, ~12 volts with key on. This is good
    2) Pin 37: 0 " , 0 " (!) This is NOT good, also try while cranking but if I remember correctly it should have 12 volts with the key on. Does the check engine light come on when they key is on but the engine is off? Just to be clear, your turning to the second position where all the dash lights are on? If the light doesn't come on then this could be going the right direction, have you tried a "known good" main relay?

    Pin 37 (with 36-2 bridge, per Bentley): ~12 volts.Will the engine start with it bridged?
    3) Pin 18: ~12 volts at all times. This is good
    4) Pins 15 and 17:
    Pin 15: 0 with ignition off, ~12 volts with key on. Oops typo, should have been pin 16, see below
    Pin 16: 0 " , 0 " , ~12 volts with 36-2 bridge.
    Pin 17: 0 " , 0 " , " . This isnt good for pins 16 and 17 as all the injectors share the same power supply wire from the main relay, this wire also supplies the idle valve, does it humm with the key on? With jumping pin 36 to 2 you are giving the main relay its own ground so double check some of the readings while cranking the engine.

    5) Pins 47 and 48: 0 (? sporadic readings) volts when engine is cranked; 517 ohms resistance.It may not be real smooth as the sensor changes voltage as the teeth of the balancer pass by it and you will notice there are gaps in the teeth, so it may be jumpy but possibly read between 1 - 3 volts, does it?
    6) Pin 45: Multi-meter reading is 3.33 at 20k ohm setting. Hmmm, this sounds on the high side but if you are real cold then this maybe Ok, I am used to 60 degrees being "cold".
    WHAT ground under the diagnostic connector?? Crap, I may be thinking of a coupe as I think the convertibles had theirs moved to the right shock tower, sorry.
    “Don't argue with idiots, they'll drag you down to their level and beat you with experience.”

    Find the problem first! Dont spend $$$$$ on parts you may not need.

    Dont be offended if I ask stupid questions, sometimes stupid fixes it.

    '87 325is The best ever
    '69 1600 My worst nightmare
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  12. #12
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    Quote Originally Posted by dandydog View Post
    But: If this thing really is just a bulb with two leads that plug into the injector connector, can somebody explain why I've got battery voltage at BOTH pins of the connector with the ignition turned on? Aren't the injectors ground-controlled through the ECU?
    The injectors aren't being grounded yet by the DME or they would be spraying fuel, since they aren't grounded you will see 12 volts on each pin since there is no load on the circuit, make sense?
    “Don't argue with idiots, they'll drag you down to their level and beat you with experience.”

    Find the problem first! Dont spend $$$$$ on parts you may not need.

    Dont be offended if I ask stupid questions, sometimes stupid fixes it.

    '87 325is The best ever
    '69 1600 My worst nightmare
    ALUMINUM BUMPER APPRECIATION ASSOCIATION (ABAA)
    Membership ID (00302)
    Joined September 14, 2005

    The secret to my success
    Reply With Quote Reply With Quote 72.132.167.81

  13. #13
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    Test results

    Okay, my tests showed no surprises, but yielded a little interesting information:
    1) When cranked for about 30 seconds, the engine did not start. (Fuel pressure: ~ 40 psi.)
    2) Immediately afterwards, the plugs were dry.
    3) Grounding pins 16 and 17 (with bridge) caused injectors to click, and the fuel pressure to drop
    (as you'd expect.)
    3A) Plugs still appear dry (??!)
    4) The plugs-on-valve-cover test yielded sparks strong enough to see in bright sunlight.
    4A) Fuel pressure leaks down quite slowly (~10 psi in 15-20 minutes.) (This came as a surprise to me because, back when the car was running, it exhibited symptoms of leaking injectors.)

    Now for your tests, GT:
    1) Pin 27: 0 with ignition off, ~12 volts with key on.
    2) Pin 37: 0 " , 0 " (!)
    Pin 37 (with 36-2 bridge, per Bentley): ~12 volts.
    3) Pin 18: ~12 volts at all times.
    4) Pins 15 and 17:
    Pin 15: 0 with ignition off, ~12 volts with key on.
    Pin 16: 0 " , 0 " , ~12 volts with 36-2 bridge.
    Pin 17: 0 " , 0 " , " .
    5) Pins 47 and 48: 0 (? sporadic readings) volts when engine is cranked; 517 ohms resistance.
    6) Pin 45: Multi-meter reading is 3.33 at 20k ohm setting.
    WHAT ground under the diagnostic connector??

    Nothing's really jumping out at me here, and I'm getting tired and discouraged. (I've been doing a batch of other - and far more rewarding - work while I putz with the Bimmer.) Tomorrow I'll try the noid light and some additional tests from the Bentley.
    What the HELL is going on with this car???
    Neil
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    Okay, so maybe this time it IS the CPU . . .

    . . . because it isn't fuel-related (it doesn't even cough on starter fluid, the plugs are wet, and the C191 connector is intact and uncorroded), and I've still got good spark. So: if i've got fuel and spark, then it's gotta be a question of WHEN I'm getting spark or fuel, right?
    Aside from the CPU, is there any other possible culprit?
    Neil

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    Yes | No

    Credit where credit is due: Both Jim Levie and . .

    . . . Geez Tech have provided valuable help during my previous problems: It's just that GT's monicker is easier to remember. (Sorry, Jim.)
    Neil

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    Yes | No
    Actually, given some thought, it's not that bad.
    Here's my logic, GT: The electronic tests show that the injectors (and the wiring TO the injectors) are working; but empirical testing (cranking the engine with a test light hooked up between the terminals of the injector connector) shows that the injectors aren't firing. Therefore, the injectors aren't BEING fired: I'd better get a new ECU, right? (First, I'm gonna repeat the noid-light test on multiple injectors, just to make sure.)
    Does this sound right to you?
    Neil
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  17. #17
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    Yes | No
    The voltage change or pulsing may happen too qickly to see it with a test light, that is where the noid light comes in. It will just be a gentle flicker.
    Make sure you have power on Pin 27 at the DME connector, this comes from the OBC relay box if you have a OBC.

    This all doesn't seem to be adding up as you had wet spark plugs before and that would have to come from the injectorsYou didn't answer on the previous suggestion of trying to start the engine with the fuel pump fuse removed and usaing starter fluid. Have you tried that?
    “Don't argue with idiots, they'll drag you down to their level and beat you with experience.”

    Find the problem first! Dont spend $$$$$ on parts you may not need.

    Dont be offended if I ask stupid questions, sometimes stupid fixes it.

    '87 325is The best ever
    '69 1600 My worst nightmare
    ALUMINUM BUMPER APPRECIATION ASSOCIATION (ABAA)
    Membership ID (00302)
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    The secret to my success
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    No problem, GT - You still have my complete confidence (and my appreciation for all your help.) Kind of makes up for that applying-two-charts-to-the-same-ECU blunder that I made, too.
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  19. #19
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    Yes | No

    Start with new spark plugs........................

    ...if they are wet then that means the injectors have been firing and you have confirmed you have spark.
    How about the basics, valve adjustment good? Timing belt intact?
    If I remember correctly your are near Denver? If so you may want to switch to a hotter spark plug considering the temperatures you drop to and the altitude you are at.
    If that doesn't help then maybe ohm out the engine temperature switch for the DME that is on the thermostat housing, it is either white or blue. I think they are around 2000 ohms when cold.
    Do I have to mention NO Platinums???? :)




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    Yes | No

    Nah, we covered the platinum thing last time.

    Thanks for signing in on this, Geez Tech.
    The plugs are new already (about the second thing I did). By my reasoning, if the timing belt had broken, I wouldn't be getting any spark; and I've switched the engine temp sensor (it's blue) out already. (I've learned a lot from our previous consultations. Thanks.)
    What may be relevant here is that, when the car died originally, it did so because the wire to the position sensor had broken. I jury-rigged the thing (with a couple of alligator clips and a carpenter's shim [to separate the clips]) in order to get home; that effort was successful, but the car wouldn't start again after that. It's possible that the shim wasn't entirely effective in preventing the clips from shorting out against each other (talk about your penny-wise and pound-foolish solutions.)
    I know the sensor operates on high voltages: If there was a short, what would have gotten screwed up?
    Thanks again -
    Neil

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