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Thread: 1986 735i - Won't Crank, Won't Click

  1. #1
    Join Date
    Jun 2018
    Location
    Houston, TX
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    4
    My Cars
    1986 735i

    Question 1986 735i - Won't Crank, Won't Click

    Hello all, first post here. I've spent a good bit of time searching through the forum and on bimmerboard to find a solution to my problem. I've had my 735i for about two years and have not experienced any significant issues other than typical problems with an aging car.

    First the background. I have a vacuum leak which I traced into the dash. I confirmed everything under the hood and under the cowl are good, the problem is downstream of the red/orange vacuum line going into the dash around the heater core. I was able to pull off a few of the components around the transmission stick, limited to the program selector switch (s/e/321) and black plastic pieces around the stick, and also pulled the ash tray. I removed one screw from the plastic cover over the vacuum lines, and the main screw holding the front of the transmission console cover down near the parking brake. While vacuum testing I was intermittently turning the car on and off to see the response from the vacuum motor. All was fine until I removed the transmission components and ashtray. The car then would not start on first attempt, but it would start after fiddling with the transmission stick and the program selector. Fiddling was arbitrary, just moved them to different positions randomly and then put the transmission back in P to attempt to start. Next day as I'm driving home from work in a driving rain, the car began to sputter and died when I pulled to the side of the road. I again fiddled with the transmission stick and the selector switch and it started one time while in N, was sputtering and promptly died. That was the last time it cranked.

    In the process of troubleshooting I've run a few things down. Things that I think could be the problem are:

    Main Relay - potentially bumped when removing the cowl to get to vacuum lines. Relay looks fine, everything is still plugged in. No further testing done yet.

    Program Selector Switch - The only electrical component removed, after which the problems started. Per the ETM it seems that it could have an effect on the start circuit, but I'm not certain if it would prevent the starter from cranking. When testing connections with the switch unplugged there doesn't seem to be any lost voltage. The starter and ignition relay/switch are getting voltage even without the switch plugged in.

    Neutral Safety Switch - Other than removing the front screw holding down the console piece I did not touch the NSS or the wiring harness & connector. Potentially something fell down into it while the plastic pieces were removed??? Battery is a little low so I'm getting about 10V at the terminals, but am also getting 10V at the starter, the starter relay and ignition switch on the column. I believe I have a good ground at the ignition relay/switch but the wiring color does not match what is shown in the ETM. Could a bad ground cause the sputtering while running? Based on this bimmerboard post I'm at a loss. https://e38.org/forums/posts/350687/

    Starter motor, main relay, wiring under the hood - Potentially swamped by heavy rain? I also came to realize that the cowls are left open to the rain and elements all the time, so something closer to the dash? The sputtering is what really has me confused. If it wasn't for that then I'm certain it's the NSS.


    Since encountering these problems I've gone ahead and removed the console pieces to expose the vacuum lines and electronics underneath. I've done a pretty thorough check for any loose wires or connectors and have not come up with any. The battery may be a little low to get the starter to crank now but I think it should still be getting the clicks from the starter solenoid (assuming that's what makes the clicking noise with a low battery). I'm certain the problem still persists despite this. I've ordered a new NSS and selector switch but they've got a 5 day fulfillment, and this is my daily driver for now. Are there any tests that can definitively pinpoint the problem? Are there any workarounds to get the car running until the new parts arrive?

    Sorry for the long post, I wanted to be thorough. Posts here have been very helpful so far, as have the ETM and google searches.
    Last edited by slam dingo; 06-25-2018 at 01:54 AM.

  2. #2
    Join Date
    Jun 2010
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    TX
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    1983/84/85 745i

    Thumbs up

    10V with the battery sitting? The car will never start like that, let alone crank. Get the battery fully charged or buy a new one if it is past four years old. Mid 12s is about fully charged. It should be a Group 48 size, H6. Make sure the terminals are clean AND tight.

    Jump the yellow/black to red under the hood at the diagnostic port and see if it cranks. I do not recall ever swapping an NSS on one of these cars. Ignition switch is a more likely culprit or there is a relay under the driver dash off the ign switch circuit. Black wire runs to the relay. These crap out at times, make sure relay is snug as are the connections.



    Once it lights off, make sure the alternator is charging. Does your battery light in the dash illuminate with the key on, engine off? That is part of the charging circuit. If dead and need quick fix, just run alligator clip to the blue wire terminal on the alternator to the fuel pump relay switched 12V signal.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  3. #3
    Join Date
    Jun 2010
    Location
    TX
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    My Cars
    1983/84/85 745i

    Thumbs up

    BTW, what part of Houston? I am in the Energy Corridor when there, few guys in Cyprus. One in Katy. One in Sugarland.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  4. #4
    Join Date
    Mar 2013
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    USA
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    465
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    E21/early e23/e34
    Agree on the 10V, once the key is turned to start (on a weak battery) the draw is pretty strong and you're actually going to read well below 10V- remember it's the Amperage that starts the car.

  5. #5
    Join Date
    Jun 2018
    Location
    Houston, TX
    Posts
    4
    My Cars
    1986 735i
    Quote Originally Posted by Hit Man X View Post
    Jump the yellow/black to red under the hood at the diagnostic port and see if it cranks. I do not recall ever swapping an NSS on one of these cars. Ignition switch is a more likely culprit or there is a relay under the driver dash off the ign switch circuit. Black wire runs to the relay. These crap out at times, make sure relay is snug as are the connections.
    For clarity, this would be a jumper between the yellow/black and red ports on the diagnostic, or the yellow/black wire on the starter?

  6. #6
    Join Date
    Jun 2018
    Location
    Houston, TX
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    My Cars
    1986 735i

    Lightbulb

    OK, quick follow up post. Went out and turned the key a few times, nothing. Got the jumper cables out and, boom. Starts right up. Now I'm feeling stupid about the ignition, however after disconnecting the jumper cables the car cranks on it's own. Jumper car was not running, the bimmer jumped off of the extra battery alone and only ran for about 1 minute before I switched it off. No possibility that the bimmer battery got a full charge for cranking. Seems I've solved one problem, but the car is still sputtering. I had the program selector switch (PSS) disconnected so I run and grab it to plug it back in. Turn the key, nothing. Reconnect jumper cables, still nothing. Pull the selector switch back off, starts right up. So I've found my bad actor for the ignition and discovered that a jump resets something in the electronics. Thinking that the PSS is also causing the sputtering I ran a jumper at the switch connector between 3 (input) and 2 (E setting). No difference, still sputtering. So now it seems I've got two unrelated problems. I didn't used to believe in coincidences.

    So now I'm scratching my head on the sputtering and leaning towards an issue from the heavy rain on the drive home. It will idle for a bit, maybe a minute max and will rev a bit when pressing the accelerator but die after a few seconds, maybe 10 max. An unrelated AC issue from the vacuum leak is that the compressor bearing and pulley is squealing and needs to be replaced. This was putting a strain on the engine before and now it kills the engine immediately if switched on. Don't think that's my culprit. Can't smell any gas and I've checked the intake up to the filter so I don't think it's a mixture problem. Must be electrical. Could this be the alternator going out? Seems somewhat similar to alternator problems I've had on other cars, but in those cases the dash lit up with warning lights and the car's ability to run slowly degraded. No lights on the dash now, and after several attempts the car reacts the same way each time. If not the alternator I must have a bad connection somewhere. I also noticed that one of the cables leading to the throttle has broken. Don't think it's related but thought I'd mention it. The car doesn't usually start quickly and I'm thinking that cable may be the reason why.
    Last edited by slam dingo; 06-25-2018 at 07:22 PM.

  7. #7
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
    My Cars
    1983/84/85 745i
    Check fuel pressure.

    Answer my other questions pls.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  8. #8
    Join Date
    Dec 2005
    Location
    Omaha NE
    Posts
    200
    My Cars
    84' 533i Turbo
    Assuming you have good clean fuel, run thru every basic test for engine electrical including inspecting grounds & cap/rotor.
    Report back on findings.

  9. #9
    Join Date
    Jun 2018
    Location
    Houston, TX
    Posts
    4
    My Cars
    1986 735i
    Hello All, been out on vacation and very busy when at home so didn't have time to post an update. Here's what I've got that's happened since my last.

    Took the alternator and battery into the parts store and both tested OK. Tech said alternator may need replacement soon however. Got back home and reinstalled both to continue the electrical diagnostics and viola, it started right up and ran normally. I have driven it for probably 200 - 300 miles since and with not even a hiccup. My best guess is one of the two relays on the side of the fuse box got wet in the storm and shorted, then later dried. I believe one is a fuel pump relay. They have rubber grommet covers that I didn't notice as they were hanging off below the relays. Just guessing that they got wet without the protection. Otherwise I'm not sure what it could be though I assume it's possible it could be any other part of the run or fuel pump circuits. I'm sure that ghost is waiting for me on the next rainy day....I'll have a look at the fuel pump and wiring in the meantime.

    I replaced the transmission selector switch and the no-cranking issue has not come back. Surprised on this one but glad I was able to diagnose.

    I was finally able to get back to diagnosing the AC vacuum leak issues and found that both the driver side external air 2-stage vent actuator and the actuator next to the steering column both leaked. I disconnected and plugged those lines for now and the AC is actually blowing out of the vents for the first time since I've had the car! I have one remaining doubt though. The defrost is still coming out as what seems like a mixture of warm and cold air. Here in Houston that presents a problem since the AC can't keep the car completely cool during the day. My question: is this the normal operating condition, or is there another defect to either the water valve or defrost flap actuator? If it is the normal condition are there any recommendations on how to rig the flap to close completely?

    Thanks for all the suggestions and help so far!

  10. #10
    Join Date
    Mar 2007
    Location
    Quadratechtown, PA
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    741
    My Cars
    5, 7, 4x4
    check the voltage regulator on the alt as those do wear out (the brushes) the alts do not wear out, generally.

    There are two dash pots that close off the cowl vents. Maybe one or both are leaking. Drivers side is two-zone for half-way and all the way open. Don't recall if vacuum opens or closes them but to keep hot humid houston out of the interior you want them to close.

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