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Thread: E24 Very long crank only on first engine run!

  1. #1
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    Question E24 Very long crank only on first engine run!

    Hello Bimmer community. First off, I am a new member and this is my first post so bare with me! I am a proud owner of a 1986 635csi. I am not too mechanically inclined but I am learning and can handle many repairs myself with guidance.

    I apologize if this topic has already been talked about but I have been through them all and I cannot find a fix for my specific issue.

    The car runs great but I am having an initial starting issue. The first start of the day gives me a 5-7 second crank until it finally "wants" to start. It then gurgles and sputters but then it idles and sounds good (insufficient fuel?). I can either 1) do as i described above and hold the key in the start position until it cranks and cranks and cranks before it finally starts... or 2) I can turn the key and crank the engine for 1 or 2 seconds, stop/back off, turn the key again right after and the car will start MUCH easier.

    Either way I start the car, this is only for my first engine start of the day. Once the car runs, I can turn it off and start again no problem.

    The car has a new battery, spark plugs and air filter. I have tested the ignition leads. I have tried to turn the key off to ignition, off, ignition, off, ignition to troubleshoot for fuel system. I read that doing this will prime the fuel pump and if the car starts...the problem lies in the fuel pump or fuel filter. But this does not change anything and I still have the issue.

    Any feedback would be helpful. Thanks guys!
    Last edited by stathipapi; 11-02-2018 at 11:34 AM.

  2. #2
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    Probably a leaking injector/CSV or a FPR. I had both cause the same issue.
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  3. #3
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    Go thru this info to check the systems before guessing what it might be.

    http://www.hiperformancestore.com/motronic.htm

    Could be leaky injectors. After a long crank before starting pull a plug and see if
    if there're fouled. If dry, no leaky injectors. If wet, well could be leaky or maybe
    because of no spark-too much fuel and fouling plugs. But, after short crank--then repeated
    starts right up? Is the total time of continuous vs with pause about the same length of time?
    The fuel pump pumps during the cranking sequence, not just ign on. Could it be taking a long time for fuel
    to get to injectors. After the short cranking is there any fuel at all in cylinders or are they
    completely dry or slightly moist? All these scenarios have to be known for analyzing the various conditions.
    All this has to be checked out, then once you know the exact problem you can
    address the issue.Don't just replace parts by thinking what it might be.

    Good luck
    Last edited by 1986series6; 11-02-2018 at 08:56 PM.

  4. #4
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    Quote Originally Posted by 1986series6 View Post
    Go thru this info to check the systems before guessing what it might be.

    http://www.hiperformancestore.com/motronic.htm

    Could be leaky injectors. After a long crank before starting pull a plug and see if
    if there're fouled. If dry, no leaky injectors. If wet, well could be leaky or maybe
    because of no spark-too much fuel and fouling plugs. But, after short crank--then repeated
    starts right up? Is the total time of continuous vs with pause about the same length of time?
    The fuel pump pumps during the cranking sequence, not just ign on. Could it be taking a long time for fuel
    to get to injectors. After the short cranking is there any fuel at all in cylinders or are they
    completely dry or slightly moist? All these scenarios have to be known for analyzing the various conditions.
    All this has to be checked out, then once you know the exact problem you can
    address the issue.Don't just replace parts by thinking what it might be.

    Good luck
    Thanks for the inputs guys. 1986series6 that is a great link! I will definitely go through that to get my six running in optimal shape (or as close to it as i can).

    I will try to diagnose if my fuel injectors are leaking. What exactly am I looking for once I pull a spark plug. Also is there any other way you can suggest I check for leaking injectors?

    Yes after a short crank (1-2 seconds), then repeated... the car starts right up. so that being said... id say the total time of pause/repeat vs continuous crank are very different. continuous cranking goes for at least 5 seconds until it shows signs of an engine start followed by gurgling then smooth idle giving me a total time of approx 8 seconds until the engine is going. where as when i crank for 1-2 seconds, pause and repeat with an instant start... total time is approx 5 seconds or less.

    the in tank fuel pump only delivers fuel when cranking? how does it prime? my issue would make sense if that pump is having trouble delivering fuel to the engine fuel pump. i will look around for ways to test the in tank fuel pump but any suggestions since we are on the topic?

    thanks again
    Last edited by stathipapi; 11-03-2018 at 08:27 PM.

  5. #5
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    I agree that link is great for troubleshooting.

    I had a related problem with long crank starts. My issue was a main relay. That's an easy and cheap thing for you to check.

  6. #6
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    The in tank pump is a primer pump for the main high pressure pump.
    So I guess there's no gurgling with the pause start method?
    Is gurgling a rough idle?
    Have to figure out the difference between the short and long start.
    Does this happen with a cold or hot start?
    Do you usually use the short method if the long doesn't start it?
    I would check with a pressure gauge for pressure and volume on both short and long starts,
    and normal engine running then follow up diagnosis on that info.

  7. #7
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    Quote Originally Posted by ldk View Post
    I agree that link is great for troubleshooting.

    I had a related problem with long crank starts. My issue was a main relay. That's an easy and cheap thing for you to check.
    Which relay are you referring to exactly?


    Quote Originally Posted by 1986series6 View Post
    The in tank pump is a primer pump for the main high pressure pump.
    So I guess there's no gurgling with the pause start method?
    Is gurgling a rough idle?
    Have to figure out the difference between the short and long start.
    Does this happen with a cold or hot start?
    Do you usually use the short method if the long doesn't start it?
    I would check with a pressure gauge for pressure and volume on both short and long starts,
    and normal engine running then follow up diagnosis on that info.
    Gurgling as in a temporary rough idle yes. There is no rough idling with the short start. Only when I do the continuous crank to get it started. and it idles rough for 5 more seconds or so then smooths out.

    This entire issue is only with the initial start of the day. so I guess a cold start. I can turn the car off and immediately start it up again no problem with 1 turn of the key. This is a new issue so I dont really have a go to method for starting. I am switching between the 2 trying to troubleshoot.

  8. #8
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    I would check fuel pressure then when the engine is off you can see if the lines are holding pressure if not check valve on fuel pump would be bad. If fuel pressure is good I would look at a dripping cold start injecttor, you can remove then and check for drops. Certainly Check pre pump.

  9. #9
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    Search this site for fuel pump relay and main relay. You'll want working spares for each of these. Locations vary. Mine are on the front of the fuse box.

  10. #10
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    Fouled plug is noticeably wet when you pull it.

    jclausen---good point about cold start valve.

    On a long crank could be too much fuel.

    On the short paused first crank the cold valve would inject just a shot of fuel and during the pause vaporize
    to make second crank fire right up.

    Kinda makes sense, I think.

    So I would do a long crank and check for fouled plugs and if they're wet jclausen diagnosis is probably correct.

    Then I would disconnect the cold start valve harness and see if it starts normally next time.
    Last edited by 1986series6; 11-05-2018 at 07:56 AM.

  11. #11
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    Thank you for all for your inputs. You've given me a solid list of things to check/troubleshoot. I'll organize all these tasks and work on it all this weekend. Ill be back with updates.

  12. #12
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    Change your voltage regulator on the alternator, cheap fix and if you don't know the history on it it's time for a new one- you'd be amazed at the differance in starting.

  13. #13
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    Quote Originally Posted by kojo96 View Post
    Change your voltage regulator on the alternator, cheap fix and if you don't know the history on it it's time for a new one- you'd be amazed at the difference in starting.
    kojo96,

    Just for my own info, how would a voltage regulator have a connection with a fuel problem?

  14. #14
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    Quote Originally Posted by kojo96 View Post
    Change your voltage regulator on the alternator, cheap fix and if you don't know the history on it it's time for a new one- you'd be amazed at the differance in starting.
    Thanks for your input. However, I installed a new refurbished alternator last month due to an unrelated problem.

  15. #15
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    Apologies if this is a silly Q... but where exactly is the check valve for the in-tank fuel pump located? is it part of the pump itself? or is it in line with the hose somewhere?

    what are your thoughts on this diy (IF the issue is in fact the check valve)... https://www.youtube.com/watch?v=6ezt4M1NZDk
    Last edited by stathipapi; 11-06-2018 at 10:34 PM.

  16. #16
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    If your thinking that the fuel in the line flows back to the tank instead of
    staying in the line may be the case. However, on your short start it
    seems fuel is pumped pretty fast to injectors to fire on second start.

    Here is one way this back flow problem was solved. http://www.bimmernut.com/forum/showt...highlight=poor

  17. #17
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    AFAIK, my 86 has no check valve. When I had my hard start issue, I installed a check valve, but it made no difference.

    One way to check is to jumper the fuel pump relay (search this forum for how to do that). This will keep the fuel pump running. If there are long starts still, it is not related to fuel leaving the lines. Otherwise, you may have found your issue.

  18. #18
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    1986series6 and Idk thanks again. I will be working on it this weekend.

    I'll test the main and fuel pump relays. I will also look into jumping the fuel pump relay.

    I'll do a long crank without starting the engine, remove and check for fouled plugs. If they are wet, could be leaking fuel injectors so ill check those after. If injectors are leaking/wet...replace? (could even be bad injector o-rings)

    Next would be to check fuel pressure. Might have to wait a bit longer for this since I do not have a pressure check kit.

    Lastly, could be fuel pressure regulator?

    Any input on my steps above would be nice. If not, thanks again and Ill update when finished.

  19. #19
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    Hey guys. You guys were a lot of help. It took me a while to get through troubleshooting but I'm back with new information.

    Summary: my 6 will not start on first engine crank but will start on 2nd turn of the key no problem.

    -fuel filter has been replaced
    -main and fuel pump relays have been tested
    -cranked the engine without starting. checked spark plugs and they are not wet (however they do have a sticky oily substance. and they are brand new)

    -most important new info: fuel pressure test
    key ignition ON = 0 psi
    engine cranking = 36 psi
    engine idle = 32 psi
    engine shutoff = 30 psi
    1 min after shutoff = 25 psi
    2 min after = 20 psi
    5 min after = 10 psi
    15 min after = 0 psi

    Questions
    1) Is this confirmation I have a faulty fuel pump check valve? (lets say the check valve is faulty for a moment. this causes the fuel to return from the lines. shouldn't i still have pressure when i turn the key to ON? instead of zero?)
    2) Is the check valve in the main or transfer pump?
    3) I can't find what the fuel pressure range should be for the 635csi. Is my 32 psi idle reading low, normal or high?

    According to http://www.hiperformancestore.com/motronic.htm if the pressure is low... replace FPR and/or fuel pump. If pressure is too high... replace FPR. So i need to find out what the optimal fuel pressure range should be.

    Thanks again guy. I await your responses.
    Last edited by stathipapi; 01-04-2019 at 12:19 AM.

  20. #20
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    I was thinking check valve as I read your last post. It is within the high pressure fuel pump. Pumps are cheap enough these days, easy to replace. I suggest removing back right wheel and access is easy. Cheapest I have found over the years has been on Amazon even after looking at Autohaus Az, FCP, RM European, Turner/ECS etc.

    https://www.amazon.com/Bosch-69418-Original-Equipment-Replacement/dp/B000BZJIDO/ref=asc_df_B000BZJIDO/?tag=hyprod-20&linkCode=df0&hvadid=312190333361&hvpos=1o1&hvne tw=g&hvrand=17896516170021620137&hvpone=&hvptwo=&h vqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9002062 &hvtargid=pla-492585592760&psc=1
    Last edited by RSheiman; 01-04-2019 at 11:41 AM.
    Rob E3

  21. #21
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    Quote Originally Posted by RSheiman View Post
    I was thinking check valve as I read your last post. It is within the high pressure fuel pump. Pumps are cheap enough these days, easy to replace. I suggest removing back right wheel and access is easy. Cheapest I have found over the years has been on Amazon even after looking at Autohaus Az, FCP, RM European, Turner/ECS etc.

    https://www.amazon.com/Bosch-69418-Original-Equipment-Replacement/dp/B000BZJIDO/ref=asc_df_B000BZJIDO/?tag=hyprod-20&linkCode=df0&hvadid=312190333361&hvpos=1o1&hvne tw=g&hvrand=17896516170021620137&hvpone=&hvptwo=&h vqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9002062 &hvtargid=pla-492585592760&psc=1

    Thanks RSheiman. The transfer pump was replaced back in 1998 but I dont have any records of the main pump being replaced (I was lucky to acquire records back to 1990 when I purchased the 6). I think the main pump should be replaced regardless if this is what is causing my problem. but I am really hoping it fixes it so I can move on to a couple fluid leak chases. Thanks for the amazon heads up. I use cdn amazon but it is still cheaper than any other place i've looked. online and local shops.

    PS. quite the impressive line up you've got. especially the e9!
    Last edited by stathipapi; 01-04-2019 at 08:42 PM.

  22. #22
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    Impressive or dumb, not sure. I only have a 2 car garage. We sadly get the most comments from my wife's 67 Mustang that has been in the family since ...well 1967.
    Rob E3

  23. #23
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    UPDATE: New fuel pump has been installed. Fuel pressure now decreases at a MUCH slower pace after engine shutdown.

    Minutes, PSI
    0, 26
    1, 26
    5, 28
    15, 25
    20, 22
    25, 18
    30, 14
    36, 10psi.....

    Before I replaced the pump I would have 0psi by 15minutes after shutdown. But i am still losing pressure somewhere.

    1) Could it be as simple as checking for leaks and tightening all my clamps? (although I am confident I tightened everything nicely)
    2) Possibly leaking fuel injectors? (although I have a receipt from previous owner and all 6 were replaced in 2006)
    3) FPR? How can I test for faulty FPR? (FPR has a fuel line coming into it and a smaller air rubber hose on the other correct?)

    Any input would be helpful. Thanks!

  24. #24
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    Well, is your problem gone or just improved? I have not seen data on PSI after shut off, someone may chime in as 10 psi may be fine............also makes sense.


    Rebuilt injectors from 2006? At some point, I would have them rebuilt, not costly. Most of us use https://www.witchhunter.com/
    Rob E3

  25. #25
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    My problem has been significantly improved. Before the main fuel pump change my fuel pressure would drop to 0-2psi within 15-20 minutes after shutdown. After the pump change it took overnight to drop to 2psi.

    I checked my files and the fuel injectors were changed (new) in 2003.
    Last edited by stathipapi; 01-08-2019 at 07:38 PM.

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