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Thread: 745i: No boost at all :-(

  1. #1
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    745i: No boost at all :-(

    Hello All
    I know there are turbo specialists here :-)

    I need your help
    I have a problem on my 1980 M102, no boost at all.
    On my boost gauge, I can read vaccum at idle, but only 0bars at full throttle.

    I read a lot of topics here but not found any solutions

    I have measured turbo play: axial play 0.05mm, and radial play 0.5mm, so it's correct.
    The turbine turn correctly and wheels are in good conditions.

    See pictures:






    I have search for leaks and found a cracked hose (n°11631273055) but no effect after new one installed.

    I took the compressions and they are good (9, 8.5, 9, 8.75, 9 and 9)

    The ignition timing is correct (12° at idle and 34° at 2000rpm).

    I don't know where to look, does anyone have an idea?

    Thank you very much

  2. #2
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    Wastegate stuck?
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  3. #3
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    99% certain your waste gate is stuck open.

  4. #4
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    Hello and thank you for your help :-)

    The wastegate is the first thing I checked.
    It is not stuck, and opens with a pressure of about 0.6-0.7 bar.

  5. #5
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    Hello all,

    I check timing chain today....timing is good.
    One question, what is the function of this valve?


    Thanks
    Last edited by gigi; 08-18-2017 at 07:16 AM.

  6. #6
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    Diverter valve could be stuck open as well. I can't see what that is in the picture you provided, and I have never seen an m102 in person so I am not sure what that valve is.

  7. #7
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    Although it might still build a little boost if the diverter valve is stuck open I'm not positive on that. It's strange that it's building zero boost. What was the procedure you used to test the wastegate if you don't mind me asking.

  8. #8
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    Hello and thanks a lot for your help :-)

    Wastegate and diverted valve are closed.

    The valve in the picture is called "Intake pressure switch" on the electric diagram and is wired to the ground and DME....I suppose it's a overboost protection....but how it work?


    To test the wastegate, i removed it and feed it with compressed air, and it start to move at approximatly 0.6bar.
    Last edited by gigi; 08-19-2017 at 04:25 AM.

  9. #9
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    Well suppose the turbo is spooling properly, it would have to be making boost it's just a question of why it's not making it to the combustion chamber. If the turbine is spinning at the proper rate it's going to create a massive amount of airflow the only way it wouldn't build pressure is a boost leak or an open diverter valve, or a wastegate that is opening prematurely or stuck open completely. That is if the turbo is good, which it sounds like it is. The system is super simple. It's got to be something easy.

  10. #10
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    Thumbs up

    Timing is set at 2200rpm and is 35° BTDC, both lines disconnected and plugged on first generation Ljet 745. BOTTOM throttle body tit hose goes to the outer side of the distributor diaphragm that faces fuel injectors. TOP throttle body tit hose goes to the back side of the distributor diaphragm that faces the spark plugs.

    Hobbs switch on firewall is for overboost, it cuts fuel injection process to stop boost. When excess boost closes the switch the car shuts down. To bypass simply disconnect.

    Pull the housings off the turbocharger, just because the wheels are free does not mean the shaft has not snapped. I have seen it before.

    Check the turbocharger to intercooler charge pipe couplings, especially the hot side ones. They can and do rot apart with age. Yours are 40 years old nearly, just go ahead and replace them.

    What is your idle vacuum? A well running 745i should be between 16-18" at 800rpm hot idle in park around 1.5% CO.



    You have either a bad turbo or a huge boost leak.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
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    Ford, MB, and GM round out the pack.



  11. #11
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    Hello everyone and thank you very much for your help and your involvement ;-)
    Some news after my holidays :-)

    The system is super simple. It's got to be something easy.
    Yes the system is simple .... but there is an enigma one mine!

    Quote Originally Posted by Hit Man X View Post
    Timing is set at 2200rpm and is 35° BTDC, both lines disconnected and plugged on first generation Ljet 745. BOTTOM throttle body tit hose goes to the outer side of the distributor diaphragm that faces fuel injectors. TOP throttle body tit hose goes to the back side of the distributor diaphragm that faces the spark plugs.

    Hobbs switch on firewall is for overboost, it cuts fuel injection process to stop boost. When excess boost closes the switch the car shuts down. To bypass simply disconnect.

    Pull the housings off the turbocharger, just because the wheels are free does not mean the shaft has not snapped. I have seen it before.

    Check the turbocharger to intercooler charge pipe couplings, especially the hot side ones. They can and do rot apart with age. Yours are 40 years old nearly, just go ahead and replace them.

    What is your idle vacuum? A well running 745i should be between 16-18" at 800rpm hot idle in park around 1.5% CO.

    You have either a bad turbo or a huge boost leak.
    Hoses are plugged correctly, and I will check the timing at 2200 rpm.

    Ok for Hobbs switch...so it's not my problem.

    I brought the turbo to a specialist for inspection, he tested it up to 1bar and told me it was working properly.

    I changed the gasket ring 11621270033 between the 2 manifolds that was dead...no result
    I have tested without exhaust...no result
    Wastegate output is sealed with a plate...yes I know it's no good at all but I will be sur that the wastegate is closed!


    I post a video here, you can see the vacuum at idle at approximately -0.6b (17") and approximately 0b at full throttle.
    It's a converted manual gearbox ;-)
    https://www.youtube.com/watch?v=LLoSNcrUqh8

    I will perform a cylinder leak down test this evening ;-)

    Thanks a lot for your help !
    Last edited by gigi; 09-14-2017 at 12:19 PM.

  12. #12
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    Hello,

    Timing at 2200rpm is 33° BTDC....I think it's not so bad...
    I checked timing with lines disconnected and plugged.

    Cylinder leak down test done....all is good, approximately 15% leak on each cylinder...

    I do not know what to do ...

    Thanks
    Last edited by gigi; 09-13-2017 at 03:46 AM.

  13. #13
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    Hello all,


    Today I removed intake manifold to inspect gaskets between intake and head for leaks....
    All seem to be good :-(
    20170916_231148.jpg


    But I see that the coolant temperature sensor near the starter is not connected, is this normal ?
    20170916_232658.jpg


    Thanks a lot
    Attached Images Attached Images
    Last edited by gigi; 09-17-2017 at 04:14 AM.

  14. #14
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    At least on M105, that sensor only affects what everyone refers to as the aftercooler fan. It goes to the relay control box up by the coolant reservoir. If the engine is warm enough (don't know the exact temp, but bet Eric does) then the electric fan kicks on and cools the turbo. Runs on a timer, so kicks off automatically.

    Has nothing to do with your lack of boost, and is not even looped in with engine management.

    No boost at all should be easy to diagnose. Vac leaks, unless MASSIVE, will not cause zero boost. Neither will exhaust leaks up wind of the turbo. Both will affect peak performance, but not likely result in no boost at all.

    I believe it is one of three things.
    1. Turbo is not spinning as it should. or
    2. Something is "open" between the turbo and the intake. Eric mentioned some possible rubber connectores. Personally, I have never worked on a M102, only M105, so I would not know where to look. I did pop a hose off on my M105 once, but it affects much more than just boost. Even without the car being under boost, there is almost no signal to the AFM, so car runs like crap always.

    3. Waste gate is sticking open.

    I know you said the waste gate was not sticking. Please check again. Remember, sticking OPEN is what will cause no boost. I had one that stuck open, and as soon as I pulled it from the manifold, it snapped back. I opened it up multiple times on the bench, put it back on and it stuck open AGAIN, as soon as the car warmed up. Just to be sure, remove it, make sure it is closed, plug the hose going to the wastegate (so that it won't open at all) and drive it judiciously. See if you get some boost.

  15. #15
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    Quote Originally Posted by lynnbilodeau View Post
    At least on M105, that sensor only affects what everyone refers to as the aftercooler fan. It goes to the relay control box up by the coolant reservoir. If the engine is warm enough (don't know the exact temp, but bet Eric does) then the electric fan kicks on and cools the turbo. Runs on a timer, so kicks off automatically.

    Has nothing to do with your lack of boost, and is not even looped in with engine management.

    No boost at all should be easy to diagnose. Vac leaks, unless MASSIVE, will not cause zero boost. Neither will exhaust leaks up wind of the turbo. Both will affect peak performance, but not likely result in no boost at all.

    I believe it is one of three things.
    1. Turbo is not spinning as it should. or
    2. Something is "open" between the turbo and the intake. Eric mentioned some possible rubber connectores. Personally, I have never worked on a M102, only M105, so I would not know where to look. I did pop a hose off on my M105 once, but it affects much more than just boost. Even without the car being under boost, there is almost no signal to the AFM, so car runs like crap always.

    3. Waste gate is sticking open.

    I know you said the waste gate was not sticking. Please check again. Remember, sticking OPEN is what will cause no boost. I had one that stuck open, and as soon as I pulled it from the manifold, it snapped back. I opened it up multiple times on the bench, put it back on and it stuck open AGAIN, as soon as the car warmed up. Just to be sure, remove it, make sure it is closed, plug the hose going to the wastegate (so that it won't open at all) and drive it judiciously. See if you get some boost.
    ... Think that sensor is one of the knock sensors, tell ECU if detonation is occurring and to richen mixture, there are 2 if memory serves me, and they are integrated into wiring harness...

    - - - Updated - - -

    Look here, lots of information.
    http://bmwturbos.scottiesharpe.com/topics/index.htm

  16. #16
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    Hello all and thanks so much for your help :-)

    Quote Originally Posted by lynnbilodeau View Post
    At least on M105, that sensor only affects what everyone refers to as the aftercooler fan.....
    Has nothing to do with your lack of boost, and is not even looped in with engine management.
    Ok

    No boost at all should be easy to diagnose. Vac leaks, unless MASSIVE, will not cause zero boost. Neither will exhaust leaks up wind of the turbo. Both will affect peak performance, but not likely result in no boost at all.

    I believe it is one of three things.
    1. Turbo is not spinning as it should. or
    I think that I have to bring it to another specialist....because I have doubt about this turbo...

    2. Something is "open" between the turbo and the intake. Eric mentioned some possible rubber connectores. Personally, I have never worked on a M102, only M105, so I would not know where to look. I did pop a hose off on my M105 once, but it affects much more than just boost. Even without the car being under boost, there is almost no signal to the AFM, so car runs like crap always.
    I check all with plug and compressed air...and I will check again....but all seem to be good.
    I even add a shaft seal to the throttle shaft to reduce leaks here...

    3. Waste gate is sticking open.

    I know you said the waste gate was not sticking. Please check again. Remember, sticking OPEN is what will cause no boost. I had one that stuck open, and as soon as I pulled it from the manifold, it snapped back. I opened it up multiple times on the bench, put it back on and it stuck open AGAIN, as soon as the car warmed up. Just to be sure, remove it, make sure it is closed, plug the hose going to the wastegate (so that it won't open at all) and drive it judiciously. See if you get some boost.
    I closed the output of the wastegate (to the exhaust) with a metal plate...so the wastegate is inhibited....

    And yesterday I checked fuel injector flow rate...approximately 280 cm 3/min at 2.5b for each, it seem to be good compared to the theoretical 271cm3/min

    Think that sensor is one of the knock sensors
    No this is not knock sensor, because it's a M102 and there is no knock detection on this engine
    Knock sensor will be installed on the left on a M106 on the picture
    20170916_232658.jpg
    Last edited by gigi; 09-19-2017 at 10:57 AM.

  17. #17
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    If you have a solid plate where the waste gate goes, then you most certainly have eliminated the waste gate as the issue. I am suspecting the turbo itself.

    And yes, you are correct, that is not a knock sensor. And yes, that boss would be drilled and tapped (along with its twin at the other end of the block) for an 8mm bolt for knock sensors if so equipped.

    Good luck. Really frustrating I know.

  18. #18
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    Quote Originally Posted by lynnbilodeau View Post
    If you have a solid plate where the waste gate goes, then you most certainly have eliminated the waste gate as the issue. I am suspecting the turbo itself.
    I think too....but I payed a turbo specialist to check it and he said it's working good...

    And yes, you are correct, that is not a knock sensor. And yes, that boss would be drilled and tapped (along with its twin at the other end of the block) for an 8mm bolt for knock sensors if so equipped.
    Exactly

    Good luck. Really frustrating I know.
    But there is something again that bothered me: to find intake air leaks, I removed the air filter and run the engine idle.
    Then I blocked the air inlet before the flowmeter with a plastic bag.
    I think it must stall the engine, but mine slow down but don't stall.
    Has anyone ever done this test?

    Thanks a lot ;-)
    Last edited by gigi; 09-20-2017 at 04:21 AM.

  19. #19
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    Eric is the resident expert on M102. As stated above, I have never worked on an M102.

    Plastic bag over the AFM intake, and it still runs?
    That is freaky for two reasons. With NO AIR going throught the AFM, it shouldn't be sending a signal for fuel.
    Even assuming you had some fuel, how does the engine run with no air getting in?

    I am just thinking out loud here; but I would THINK that if you had a huge vac leak, the engine wouldn't run at all. Very strange.

  20. #20
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    Quote Originally Posted by lynnbilodeau View Post
    Eric is the resident expert on M102. As stated above, I have never worked on an M102.

    Plastic bag over the AFM intake, and it still runs?
    That is freaky for two reasons. With NO AIR going throught the AFM, it shouldn't be sending a signal for fuel.
    Even assuming you had some fuel, how does the engine run with no air getting in?

    I am just thinking out loud here; but I would THINK that if you had a huge vac leak, the engine wouldn't run at all. Very strange.
    As you said....very strange !
    i'm not a young beginner in mechanic, but this engine makes me crazy!

    Yes engine is running with a bag on AFM (at idle only).
    For me, it's can working because at throttle closed, idle map is used to control injection and idle map don't use the AFM signal (not sure about it...)
    BUT you are right, the question is "where does the air come in"?
    For me 2 possibility:
    1- Vacuum leak somewhere in the intake (don't find until now...) but this is the reason I removed the intake manifold and I have to test it for leak with the 6 outlets blocked and compressed air injected through the throttle body.
    2- Air is entering somewhere in the crankcase (through shaft seals behind flywheel or vibration damper, crankcase gasket, timing cover gasket or cover head gasket...) and go in the ontake through the breather hose...

    PS: Eric is Hit Man X ?

  21. #21
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    Yes.

  22. #22
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    Quote Originally Posted by lynnbilodeau View Post
    Yes.
    Ok thanks, hope he will come here again...

  23. #23
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    Hello all.

    Some news...

    I worked wood to make a plate to search leaks at intake manifold with compressed air.
    20170923_132711.jpg

    20170923_162614.jpg
    Result: no leak at all (with shaft seal mounted on throttle shaft)

    So I mounted the plate on the cylinder head to do the same...
    I inflate the engine at 2bar but pressure decrease rapidly to 0.
    I think it's normal because piston rings are not 100% "waterproof".
    20170924_180331.jpg

    So, today I make a puzzle...
    20170925_185542.jpg

    I'll sandblast it with glass balls and replace all the wear parts.
    Last edited by gigi; 09-27-2017 at 08:49 AM.

  24. #24
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    Some news ....
    Rebuilding turbo with new service kit after cleaning and sandblasting:

    20170930_183936.jpg

    20171002_181542.jpg

    20171005_202750.jpg
    Last edited by gigi; 10-06-2017 at 03:52 AM.

  25. #25
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    If you put a plate over the hole where the wastegate bolts down you are not going to do anything but seal the exhaust leak the valve must be seated inside the manifold to keep exhaust from bypassing the turbo hotside when the valve is pushed/pulled up it allows the exhaust to bypass turbo hotside thereby reducing boost. Blocking off the hole at the top of the manifold leaves the bypass passage wide open.

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