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Thread: 540i e34 6speed wierd start and its driving me crazy

  1. #1
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    540i e34 6speed wierd start and its driving me crazy

    Ok so I've had this e34 540i in my life since I was only 7 years old and the moment I layed eyes on it I knew i had to have it. Long story short it's always started like this but i finally got around to trying to fix it. It began with normal cold starts the engine would turn right over with no hesitation. But once it got warm, turning it over took an extra second or two will a little hesitation. I began with changing both coolant temp sensors and the car did great the 1st day. However the next day when it went to cold start it, it acted how it did before when it was warm. After burning my hands with hot coolnt, trying to mess with the sensors, I thought to reach out to anyone who may have an idea as to what can cause this, the car runs great with perfect power and no hesitation so I know it's not a the fuel pump or anything like that. Any help is much appreciated thanks in advance!
    Last edited by Loomi540i; 09-14-2018 at 08:21 PM.

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  3. #3
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    As long ad the gauge appears to be reading okay. I would start with changing the coolant temp sensor for the DME, no need to change both.

    The coolant temp sensor is a knownn m60 problrm, when it reads out of range the DME dumps massive amounts of fuel flooding the engine and ring seal washing the cylinder walls so the engine can't build compression that results in a no start condition.

    Start with the temp sensor to the dme.

  4. #4
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    [QUOTE=Mykk;30105946]As long ad the gauge appears to be reading okay. I would start with changing the coolant temp sensor for the DME, no need to change both.

    I did change both coolant temperature sensors and the problem persists but in a slightly different manor

    - - - Updated - - -

    How do I do that? Im new to forums

  5. #5
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    I feel like I'm taking stabs in the dark, but next I would investigate fuel pressure regulator. It's located at the end of the fuel rail on the engine. That location is susceptible to engine heat. If it's bleeding pressure back to the tank once the engine is turned off I can see how there would be extended cranking to build pressure in the fuel line again. My '95 540i/6 doesn't have a prime pulse with key on so it only builds fuel pressure while cranking and running. Again, that's a random stab in the dark.

  6. #6
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    Well I already ordered a new fuel pressure regulator and 2 new fuel filters from FCPeuro considering I still have the original filters, should be here soon I will put them on and hopefully makes it better. Do you have an Instagram btw? I can send you the video maybe It would be more helpful

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    Quote Originally Posted by Mykk View Post
    I feel like I'm taking stabs in the dark, but next I would investigate fuel pressure regulator. It's located at the end of the fuel rail on the engine. That location is susceptible to engine heat. If it's bleeding pressure back to the tank once the engine is turned off I can see how there would be extended cranking to build pressure in the fuel line again. My '95 540i/6 doesn't have a prime pulse with key on so it only builds fuel pressure while cranking and running. Again, that's a random stab in the dark.
    Yesterday 10:55 PM
    Well I already ordered a new fuel pressure regulator and 2 new fuel filters from FCPeuro considering I still have the original filters, should be here soon I will put them on and hopefully makes it better. Do you have an Instagram btw? I can send you the video maybe It would be more helpful

  8. #8
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    Quote Originally Posted by Loomi540i View Post
    the engine would turn right over with no hesitation. But once it got warm, turning it over took an extra second or two will a little hesitation.
    Turned over with/without hesitation - t.i. a pause between the key going to Start and the engine actually rotating - or fired up with/without a pause - engine's turning but not firing? The former is probably a worn starter or bad grounds. The latter could be a sensor issue, or fuel pressure. Have you tested the sensors? How about fuel pressure? Just because it runs right normally does not rule out pressure issues.

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    Quote Originally Posted by moroza View Post
    Turned over with/without hesitation - t.i. a pause between the key going to Start and the engine actually rotating - or fired up with/without a pause - engine's turning but not firing? The former is probably a worn starter or bad grounds. The latter could be a sensor issue, or fuel pressure. Have you tested the sensors? How about fuel pressure? Just because it runs right normally does not rule out pressure issues.
    Do you have an Instagram? I can send you te video to clarify. And yes it's the 2nd one you described.

  10. #10
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    I don't use Instagram. Recommend you check fuel pressure.

  11. #11
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    Quote Originally Posted by moroza View Post
    I don't use Instagram. Recommend you check fuel pressure.
    Oh ok got it, I did order a new fuel pressure regulator so i will see what happens after that as well as new fuel filters

  12. #12
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    Hard starts when hot are normally related to failing fuel pressure regs. From my understanding and what I was taught the fuel can basically “boil” in the regulator causing “vapor lock”, Or I’ve seen it cause the fuel to leak back into the tank. This is a common 108/107 Mercedes problem, the only bmw ive had this happen in was an m10 powered e30.

    I think these guys have pointed you in the right direction, replace the pressure reg and report back what you find
    Last edited by e30luv318i; 09-16-2018 at 04:05 PM.
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  13. #13
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    Quote Originally Posted by e30luv318i View Post
    Hard starts when hot are normally related to failing fuel pressure regs. From my understanding and what I was taught the fuel can basically “boil” in the regulator causing “vapor lock”, Or I’ve seen it cause the fuel to leak back into the tank. This is a common 108/107 Mercedes problem, the only bmw ive had this happen in was an m10 powered e30.

    I think these guys have pointed you in the right direction, replace the pressure reg and report back what you find
    10-4 will do!

  14. #14
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    You can buy a Harbor Freight fuel pressure gauge for like $20, instead of throwing parts at it.
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    You an also rent a fuel pressure tester from the likes of Autozone etc. From the sounds of it, you'd have to test when the problem is active, so there'll be some trial and error. Also, don't look past the possibility of a vacuum leak. Understood that a wide vacuum leak will throw a code, but just keep it in the back of your mind.





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  16. #16
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    Quote Originally Posted by Trasportador View Post
    You an also rent a fuel pressure tester from the likes of Autozone etc. From the sounds of it, you'd have to test when the problem is active, so there'll be some trial and error. Also, don't look past the possibility of a vacuum leak. Understood that a wide vacuum leak will throw a code, but just keep it in the back of your mind.
    Well I changed the fuel pressure regulator and the 2 fuel filters and that did not solve the problem. Not surprised, was gonna change them anyway, but the cars runs 100% so it's hard to narrow down what it can be. Is there anyway I can upload the video here to show you guys how it starts?

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    I'm not understanding why you won't hook up a fuel pressure gauge. It could be any number of fuel related issues, that you would never be able to isolate without a gauge. Could be the fuel pump check valve bleeding off, or the injectors leaking, etc...

    Did you check the resistance of the temp sensor before swapping it out? Are you swapping out perfectly good OEM parts for questionable quality aftermarket parts? You could be creating problems, instead of fixing them.
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    Quote Originally Posted by JGood325 View Post
    I'm not understanding why you won't hook up a fuel pressure gauge. It could be any number of fuel related issues, that you would never be able to isolate without a gauge. Could be the fuel pump check valve bleeding off, or the injectors leaking, etc...

    Did you check the resistance of the temp sensor before swapping it out? Are you swapping out perfectly good OEM parts for questionable quality aftermarket parts? You could be creating problems, instead of fixing them.
    I get all my parts from fcp eurp. All OEM parts. And also where do I hook up the pressure guage?

  19. #19
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    You hook up the gauge anywhere between the pump and the fuel rail. You just T into the fuel hose, and monitor pressure. You may have to leave it hooked up for a day or two since your problem appears to be intermittent. If you notice you have insufficient pressure at the times when it won't fire, then you can continue chasing a fuel issue (install a check valve, test fuel injectors, etc). If not, then you know to move on.

    Doesn't matter where parts are sourced from. FCP carries a number of brands, many of which are not the equivalent of OE. Even quality OE parts can be faulty, so when you throw parts at a car to fix something, you open yourself up the the possibility of introducing a new problem which can complicate troubleshooting of the existing problem. For instance, I bought a Lemforder idler arm to try to correct a stiff/sticking steering issue. That created a new issue, as the Lemforder idler ball joint taper was not drilled correctly, so it didn't seat properly. The original issue turned out to be bad steering shaft u-joints.
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  20. #20
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    Quote Originally Posted by JGood325 View Post
    You hook up the gauge anywhere between the pump and the fuel rail. You just T into the fuel hose, and monitor pressure. You may have to leave it hooked up for a day or two since your problem appears to be intermittent. If you notice you have insufficient pressure at the times when it won't fire, then you can continue chasing a fuel issue (install a check valve, test fuel injectors, etc). If not, then you know to move on.

    Doesn't matter where parts are sourced from. FCP carries a number of brands, many of which are not the equivalent of OE. Even quality OE parts can be faulty, so when you throw parts at a car to fix something, you open yourself up the the possibility of introducing a new problem which can complicate troubleshooting of the existing problem. For instance, I bought a Lemforder idler arm to try to correct a stiff/sticking steering issue. That created a new issue, as the Lemforder idler ball joint taper was not drilled correctly, so it didn't seat properly. The original issue turned out to be bad steering shaft u-joints.
    Hmm well I got the brand called Meistersatz, it was the only one they carried

  21. #21
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    Quote Originally Posted by Loomi540i View Post
    Hmm well I got the brand called Meistersatz, it was the only one they carried
    That's aftermarket. FCP also carries the OEM Bosch sensor for the m60, for about 1/2 of the price. There's likely nothing wrong with your brand new sensor, I'm sure it works perfectly fine. But now you've replaced an OEM coolant temp sensor (not exactly a wear item) with aftermarket part for no reason, instead of just pulling a multimeter out and checking the resistance at various temperatures. You're essentially downgrading your car by throwing parts and money at it. That's my whole point here, I'd avoid doing that...
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  22. #22
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    Quote Originally Posted by JGood325 View Post
    That's aftermarket. FCP also carries the OEM Bosch sensor for the m60, for about 1/2 of the price. There's likely nothing wrong with your brand new sensor, I'm sure it works perfectly fine. But now you've replaced an OEM coolant temp sensor (not exactly a wear item) with aftermarket part for no reason, instead of just pulling a multimeter out and checking the resistance at various temperatures. You're essentially downgrading your car by throwing parts and money at it. That's my whole point here, I'd avoid doing that...
    Well here's the thing, after replacing that sensor it started up perfect everytime for that day! But the next day it began doing it again. When I disconnect it and reconnect it, it starts up perfect. Then back to the problem the next time I start it. Btw do you have an Instagram? I feel like it would help if I sent you the video

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    Quote Originally Posted by Loomi540i View Post
    Btw do you have an Instagram? I feel like it would help if I sent you the video
    I don' use Instagram either. Post it up on youtube. Maybe someone will watch it.
    demet

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