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Thread: Hard start when engine is warm.

  1. #1
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    Angry Hard start when engine is warm.

    Hey all, 95 m3 S50,it runs perfect. Starts perfect cold and starts perfect warm/hot. Provided I restart it within 5min of letting it sit. Stop for fuel or a quick in and out at 7-11 and it starts every time. Should I take longer like 10-15 min or any length of time past that it starts hard. The engine turns over from the starter but doesn't fire up. I can crank it for 30 sec to a min straight and it won't fire. I've had this trouble for some time now. I learned that just quick little attempts at starting it works best. Just hit the key enough to turn it one or twice over and release it. 2 out of 5 times it just starts and runs flawlessly.Try and just hold the key for a long crank and you could run the battery dead without it firing. This only happens when the motor is warm and it sits for longer than 10+ min. I leave it for hrs and it will start normally so I know its temp related. I've scanned it with no codes. Had three BMW shops and the dealer attempt to repair it. Injectors are new. Swapped HFMs still does it. I've been told its a faulty ICV~sticking? Possible crank pos sensor. I've spend 500 bucks in diagnostics alone. This is really starting to piss me off. Its embarrasing to sit in a busy parking lot trying to get your bimmer to start. It always will but often only after a long series of attempts. ANY help is appreciated.
    Last edited by lorkar; 05-04-2007 at 10:05 PM.
    My E36 SC S52 OBD1 Vert is sold. (I miss her already)
    E46 M3 Vert my new obsession.~soon to be boosted!

    My 95 M3 coupe for sale. (was supercharged) available seperatly.(SOLD)

  2. #2
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    Heat soak
    Fuel pump relay
    Fuel pump
    ICV
    Crank position sensor
    Winter fuel

  3. #3
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    i would say engine coolant temp. sensor might be bad
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  4. #4
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    Quote Originally Posted by NicoyaM3 View Post
    i would say engine coolant temp. sensor might be bad
    OP doesn't complain of bad gas mileage or rough idle or low power so that's not as likely a cause.

  5. #5
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    Quote Originally Posted by Balthazarr View Post
    Heat soak
    Fuel pump relay
    Fuel pump
    ICV
    Crank position sensor
    Winter fuel
    Not fuel...been going on since august last yr...I ordered an ICV and a Crank Position sensor...picked up a fuel pump relay and a new pump...any more suggestions are apprecitated.

    Elaborate on "heat soak"....thanks again.
    My E36 SC S52 OBD1 Vert is sold. (I miss her already)
    E46 M3 Vert my new obsession.~soon to be boosted!

    My 95 M3 coupe for sale. (was supercharged) available seperatly.(SOLD)

  6. #6
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    hmm..i had a problem with cold starts and when i asked a mechanic he told me it was the battery. he also told me when the alternator goes bad the car starts up fine when cold but has trouble when its warm.



    Quote Originally Posted by D Unit View Post
    Coupe owners know their rides are hot, whereas, Sedan owners constantly feel the need to explain or defend why their cars have 4 doors. Because Sedan owners deal with this insecurity problem daily, they have dedicated a special group to cope with their issues. I think it's called the M3/4 Club or something like that...

  7. #7
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    Engine temp can increase after shutdown.
    Fuel lines can be heated and cause a vapor lock.
    Boosted engines as an example create a lot of heat and require water/alcohol injection to mitigate the effect by cooling the charge.

    Another problem is the starter can bind if it gets too hot creating added resistance.
    As a result, the engine cranks slowly.
    You would need to do an amp load test to see if this happens.
    Last edited by Balthazarr; 04-18-2007 at 11:20 PM.

  8. #8
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    I'm the only one in the world with this problem?
    My E36 SC S52 OBD1 Vert is sold. (I miss her already)
    E46 M3 Vert my new obsession.~soon to be boosted!

    My 95 M3 coupe for sale. (was supercharged) available seperatly.(SOLD)

  9. #9
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    Ok, new ICV and it still does it. (although it cured my cold start stall when stopping at lights) so not a total loss. This was a bitch to change. especially with the supercharger. New fuel pump relay~didn't think it was that but it was cheap and old so its new now. Still does it. I have a new crank position sensor its going in tomorrow.

    Again anyone with similar symtoms please chime in.
    My E36 SC S52 OBD1 Vert is sold. (I miss her already)
    E46 M3 Vert my new obsession.~soon to be boosted!

    My 95 M3 coupe for sale. (was supercharged) available seperatly.(SOLD)

  10. #10
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    i had similar issue w/ another make - same symptoms but only after running on hot days w/ AC on. Seems it was a vapor lock issue. Some kind of purge valve or vacuum hose issue - sorry not able to be more specific - a long time ago - but hope that helps.
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  11. #11
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    similar symptoms here, also supercharged.

    #1. Going from any gear to Neutral, frequently RPM jumps up/down, until it settles. I think I need new ICV even though it was cleaned several times (but has scratches on the moving part inside already)

    #2. When engine warm, after it's shut off for some period, it won't start until it cools down (only hear tick from starter), I got starter hot wired directly from battery so if that happens I press the button and starts. This could be starter but I am not sure.

  12. #12
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    Quote Originally Posted by M3Scharged View Post
    similar symptoms here, also supercharged.

    #1. Going from any gear to Neutral, frequently RPM jumps up/down, until it settles. I think I need new ICV even though it was cleaned several times (but has scratches on the moving part inside already)

    #2. When engine warm, after it's shut off for some period, it won't start until it cools down (only hear tick from starter), I got starter hot wired directly from battery so if that happens I press the button and starts. This could be starter but I am not sure.

    Yes the ICV did settle my RPM bounce coming to stops and my cold start stalls at lights. I clean it once and it make almost no difference. I replaced it and was pleased.

    Your problem does sound like it a starter problem. My turns over fine at regular cranking speed . It just doen't fire up. Cool it off and it starts fine. Warm it up and shut down for 5 min, starts fine. Let it sit for ten-15 min....its a long hard start.
    My E36 SC S52 OBD1 Vert is sold. (I miss her already)
    E46 M3 Vert my new obsession.~soon to be boosted!

    My 95 M3 coupe for sale. (was supercharged) available seperatly.(SOLD)

  13. #13
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    I've noticed that if I make short trips (like 2 miles) it can take several tries to start mine up... also running a supercharger setup. I hate making short 2-3 miles trips but I have to do it on a daily basis because I have 4 buildings to support.

  14. #14
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    Bumping this ancient thread.

    Supercharged '96 M3.
    Long-crank issue when hot, otherwise it starts normally. No codes.
    I had the tuner reduce hot start cranking fuel by 20%, and that improved it quite a bit but did not cure it completely. I am waiting for him to get back from vacation to attempt to remove even more hot cranking fuel, but I am curious as to whether this is a symptom of another problem and changing the fuel is a bandaid.

    Has anyone fixed this problem?

  15. #15
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    Quote Originally Posted by 1000hp View Post
    Bumping this ancient thread.

    Supercharged '96 M3.
    Long-crank issue when hot, otherwise it starts normally. No codes.
    I had the tuner reduce hot start cranking fuel by 20%, and that improved it quite a bit but did not cure it completely. I am waiting for him to get back from vacation to attempt to remove even more hot cranking fuel, but I am curious as to whether this is a symptom of another problem and changing the fuel is a bandaid.

    Has anyone fixed this problem?
    Have hot start problem with my euro s50b30. A quick pump of the accelerator pre hot start gets it to fire otherwise it’s just turns over.

    On another forum I’ve been advised to check fuel pressure or replace FPR (fuel pump regulator/relay). Alternatively it could be the DME. How is your tuner adjusting?


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  16. #16
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    are slow.
    Usually ends up being an issue with a sensor or a fuel related problem.

    I had a problem where the when warm the engine would crank really slowly, but that ended up being the starter. Doesn't sound like your problem.

    You should get a fuel pressure gauge and test when the engine is cold, and then again test it when it's warm. Have someone start the car so you can read the gauge, or better yet mount a camera pointing at the gauge and review.

    Relevant link:

    http://www.bimmernut.com/forum/showt...is-warm-(M20)?

    - - - Updated - - -

    Quote Originally Posted by 1000hp View Post
    Bumping this ancient thread.

    Supercharged '96 M3.
    Long-crank issue when hot, otherwise it starts normally. No codes.
    I had the tuner reduce hot start cranking fuel by 20%, and that improved it quite a bit but did not cure it completely. I am waiting for him to get back from vacation to attempt to remove even more hot cranking fuel, but I am curious as to whether this is a symptom of another problem and changing the fuel is a bandaid.

    Has anyone fixed this problem?
    Are you on the stock fuel pump and FPR?
    "Be who you are and say what you feel because those who mind don't matter and those who matter don't mind."
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    DIY BMW Tools. Charlie For President

  17. #17
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    Quote Originally Posted by Hova View Post
    Are you on the stock fuel pump and FPR?
    Yes. Fuel pressure is good. I believe it is in the tune.

    I did find that with the m50 manifold on my s52, the #6 intake runner (and the intake air temp sensor that lives there) sit directly above the heater hoses where they enter the firewall. As a result, that one runner is about 20*F higher than the others, and the measured intake air temperature matches. I would love to know how the DME compensates for IAT during cranking. But, iff anything, I believe it would lean it out more and more the higher the IAT is. So that is probably not the issue.
    I will try unplugging the IAT sensor for a hot start and see if that helps. I'm thinking it won't, but we shall see.

  18. #18
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by 1000hp View Post
    I did find that with the m50 manifold on my s52, the #6 intake runner (and the intake air temp sensor that lives there) sit directly above the heater hoses where they enter the firewall. As a result, that one runner is about 20*F higher than the others, and the measured intake air temperature matches.
    Should be relatively easy to wrap some foil insulation around that heater hose.

    Neil

  19. #19
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    Quote Originally Posted by NeilM View Post
    Should be relatively easy to wrap some foil insulation around that heater hose.

    Neil
    I was thinking either that or relocate the sensor. The foil would be much easier.

  20. #20
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    See if it will start and run for a few seconds on starter fluid or carb cleaner. This way you know you have spark.

  21. #21
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    Quote Originally Posted by marvinstockman View Post
    See if it will start and run for a few seconds on starter fluid or carb cleaner. This way you know you have spark.
    This.

    Would also clear out any issues with sensors, and point towards it being a fuel issue.
    "Be who you are and say what you feel because those who mind don't matter and those who matter don't mind."
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  22. #22
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    Bumping this thread again, any solutions? I have a similar issue, S50B30us. Starts fine when cold, just cranks and cranks when it’s hot. Previous owner of engine had similar issue, just not as bad; he could always get it to start. I could kill the battery cranking this thing when it’s hot. Engine cranks really fast, almost like it’s not getting fuel. Idle is somewhat jumpy when cool, levels off at temp. Engine runs great when it does manage to get going. Strong fuel smell at tailpipe when it doesn’t start. Things I’ve done/checked/replaced:
    •Previous owner installed oem crank & cam sensors, symptoms persist
    •changed crank pulley with known working unit
    •new fuel filter
    •new fuel pumps (BW dual setup)
    •coils and coil boots with matching, known working units
    •new NGK R 6962 spark plugs
    •swapped ECU with known working unit
    •swapped chip with known working unit
    •fuel press reg vac line attached/in tact/no kinks
    •fuel pump relay
    •fuel pressure regulator with known working unit
    The fast crank thing gets me. Not sure what else there is to check. Someone help me, I’m at the end of my rope with this thing
    Last edited by S50ti; 08-06-2021 at 03:29 PM.

  23. #23
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    Quote Originally Posted by S50ti View Post
    Bumping this thread again, any solutions? I have a similar issue, S50B30us. Starts fine when cold, just cranks and cranks when it’s hot. Previous owner of engine had similar issue, just not as bad; he could always get it to start. I could kill the battery cranking this thing when it’s hot. Engine cranks really fast, almost like it’s not getting fuel. Idle is somewhat jumpy when cool, levels off at temp. Engine runs great when it does manage to get going. Strong fuel smell at tailpipe when it doesn’t start. Things I’ve done/checked/replaced:
    •Previous owner installed oem crank & cam sensors, symptoms persist
    •changed crank pulley with known working unit
    •new fuel filter
    •new fuel pumps (BW dual setup)
    •coils and coil boots with matching, known working units
    •new NGK R 6962 spark plugs
    •swapped ECU with known working unit
    •swapped chip with known working unit
    •fuel press reg vac line attached/in tact/no kinks
    •fuel pump relay
    •fuel pressure regulator with known working unit
    The fast crank thing gets me. Not sure what else there is to check. Someone help me, I’m at the end of my rope with this thing
    Measure the fuel pressure and ensure your fuel injectors match the tune (and or the tune isn't some over fueled junk). MEASURE, not list off "known working parts". Fuel pressure should be 43.5psi at idle with the vacuum line attached to the FPR. It should read 51psi with the vacuum line removed. Any deviation 10% or higher would indicate over fueling by over pressurization.

    This happens on B32 SC cars when we bump up to 4.0bar fuel pressure regulator and 10psi pulley configs for a ghetto "tune" fix. Too much fuel is being dumped in so the engine floods.

    You can avoid your hot start issue by revving the car to 3k rpms and killing the ignition (while at 3k rpm) every time you shut the car off. You will never have a hard hot start issue after. If you get stuck in a hot start flood, you can just pull the fuel pump fuse and crank till the engine starts and then dies out. Then reinsert the fuse and start as you normally would.
    Last edited by Braymond141; 08-06-2021 at 05:11 PM.

  24. #24
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    Wow, thanks man. I’ll ghetto-hack a fp gauge in at the front of the rail and report back my findings. What would be the fix for over pressurization, a different tune? What does the 3k RPM trick actually do?
    Last edited by S50ti; 08-06-2021 at 05:56 PM.

  25. #25
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    Quote Originally Posted by S50ti View Post
    Wow, thanks man. I’ll ghetto-hack a fp gauge in at the front of the rail and report back my findings. What would be the fix for over pressurization, a different tune? What does the 3k RPM trick actually do?
    Over pressurized is a hardware issue, not a tune issue. Ensuring the injectors match the tune and that the tune isn't junk is a whole separate task. Do everything mentioned, not just one.

    It clears the combustion chambers of fuel on shut off that way when you go to restart it isn't compounding the extra fuel issue you obviously have.

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