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Thread: Starting issue, well....sometimes

  1. #1
    Join Date
    Feb 2019
    Location
    Fredericksburg,VA
    Posts
    8
    My Cars
    1979 BMW 733i

    Starting issue, well....sometimes

    Ok, I have finally figured out all my no start issues I had after doing the fuel pump replacement and was good for a couple days. Then I had issues with the starter solenoid not contacting correctly and would pull in but not pass current to the starter. It would also explain the 2 times I had the starter continue to run after removing the key from the ignition as the contactor likely stuck on those times. I replaced the SR41x with a SR95x which is what the "replacement" seemed to be. After I ordered it I noticed a thread on the MyE28 board that perhaps it would have been smarter to go with the SR441x but alas I already had the 95 coming.

    I had a fun time getting to the top nut to get my starter off but did it with a combination of a box wrench I bent and one I cut off to be a box end only stubby wrench. The #6 intake runner had to come off to even attempt getting to the nut and I am very happy it was a nut and not a bolt as some posts I found would have indicated. It looked like the previous person that put a re-man on used a chisel to tighten the nut the last time. After I got the new one installed, which went in surprisingly easier, I turned the key to start it and......nothing. No click, no groan, just a whir of some pump that I couldn't have heard before and the fuel pump whirring away. I double checked all the connections were on the right posts and I even poked them with a B+ jumper wire and the starter took off just like it should. Right now, when this happens, I have an extra wire on the "trigger" connection on the starter and I touch the B+ post of the battery leaving the key in the run position it returns to from start position when it fails and it fires right up. I watched the trigger wire on the starter with a meter to see if it is getting anything. .... When it starts properly the line has 11+ volts on it, however, when it fails it only has like 6-7 volts on it.

    I knew the battery that was in it was 1) old and 2) too small. I installed a group 48(H6) battery in it yesterday which fits nicely and will give me a bit more punch this winter. I also replaced the voltage regulator on the alternator since when I measure the charging voltage it seems low(like 13.6 as I recall) and it was an easy job to do. The new vr is putting out the same voltage as the old one. I had purchased a known good used ECU and have swapped that out with my original thinking it might be part of the problem. Both do the exact same thing.

    I am at a complete loss as to even begin figuring out what is not happy.
    Thoughts?
    Scott
    1979 733i

  2. #2
    Join Date
    May 2013
    Location
    Fredericksburg, VA
    Posts
    390
    My Cars
    1985 745i
    Ignition switch issue?

    Steve H., Fredericksburg, VA
    1984 733i, 265/6 & M106 turbo swap project. Working AC!
    1985 745i, parting out

  3. #3
    Join Date
    Feb 2019
    Location
    Fredericksburg,VA
    Posts
    8
    My Cars
    1979 BMW 733i
    You know, the thought crossed my mind too so I found a NOS switch on ebay and have it coming. Naturally my switch is different than everything newer than '79. Looks to be they changed the connector from a female socket to a male socket on the switch side and not backward compatible. And the newer one is about 1/2 the price.

    I also just went out to the garage and turned the key and it fired right up. I tried it 2 more times and it worked all 3 times. That gets me wondering if it is a thermal issue with something. When it failed earlier today it was up to normal operating temps whereas first thing this morning and now the engine bay is completely cold. I think I am going to buy some electronic freeze spray and start blasting stuff after heating it up.
    Scott
    1979 733i

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