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Thread: M50TU MLS .140 Problem

  1. #1
    Join Date
    Mar 2019
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    PA
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    My Cars
    94 325i

    M50TU MLS .140 Problem

    I am in the process of doing a turbo build on my M50TU, and to kick things off I opted to use the Cometic MLS .140 head gasket. The install seems to have gone as planned for the most part, however I am having an issue in the lower RPM range now.

    Just a little bit on insight into what I did:
    - Head was sent off to the machine shop to be resurfaced. I also had the valve seats grinded, valves restemmed, and valve seals replaced
    - MLS .140 HG w/ copper spray
    - ARP head studs (did a torque sequence of 25/25/50/50/75/75)
    - Battery disconnected for 3+ weeks
    - Replaced oil with 0w-40 Mobil1

    The engine builder that did the machining on my head said that since the valve stems were raised 5/1000ths, I would need to adjust valve lash.. which the engine should do on it's own because it has hydraulic lifters.

    Now to get to the point. Ever since I reassembled the engine and fired it up, it has been having trouble in the low RPM range. The low end power is non existent, and if I lightly press the throttle, the engine will hesitate and die out. When I drive the car, I have to keep pressing the gas peddle semi-rapidly to get the RPMs up so I can take off. I can smell fuel inside the cabin, but I've inspected the engine around the fuel components and do not see any leakage. Once the engine hits around ~3500-4000 RPM it runs flawlessly, and achieves a nice healthy hard pull. I don't daily the car, but I just wanted to be able to drive it before I get the rest of the turbo parts installed. I have driven the car roughly 15 miles since reassembly, just in case the ECU needs to relearn or something of the likes.

    Am I missing something? Perhaps I forgot to install something? Has anybody else driven their M50TU on a lowered compression without boost? Will this have to be corrected with a tune?

    Thanks in advance

  2. #2
    Join Date
    Jun 2012
    Location
    Socal
    Posts
    298
    My Cars
    turbo e36
    Quote Originally Posted by xbrxlunch View Post
    I am in the process of doing a turbo build on my M50TU, and to kick things off I opted to use the Cometic MLS .140 head gasket. The install seems to have gone as planned for the most part, however I am having an issue in the lower RPM range now.

    Just a little bit on insight into what I did:
    - Head was sent off to the machine shop to be resurfaced. I also had the valve seats grinded, valves restemmed, and valve seals replaced
    - MLS .140 HG w/ copper spray
    - ARP head studs (did a torque sequence of 25/25/50/50/75/75)
    - Battery disconnected for 3+ weeks
    - Replaced oil with 0w-40 Mobil1

    The engine builder that did the machining on my head said that since the valve stems were raised 5/1000ths, I would need to adjust valve lash.. which the engine should do on it's own because it has hydraulic lifters.

    Now to get to the point. Ever since I reassembled the engine and fired it up, it has been having trouble in the low RPM range. The low end power is non existent, and if I lightly press the throttle, the engine will hesitate and die out. When I drive the car, I have to keep pressing the gas peddle semi-rapidly to get the RPMs up so I can take off. I can smell fuel inside the cabin, but I've inspected the engine around the fuel components and do not see any leakage. Once the engine hits around ~3500-4000 RPM it runs flawlessly, and achieves a nice healthy hard pull. I don't daily the car, but I just wanted to be able to drive it before I get the rest of the turbo parts installed. I have driven the car roughly 15 miles since reassembly, just in case the ECU needs to relearn or something of the likes.

    Am I missing something? Perhaps I forgot to install something? Has anybody else driven their M50TU on a lowered compression without boost? Will this have to be corrected with a tune?

    Thanks in advance

    I used to have a M50b25TU with .140mls...it was a dog down low, but it did drive fine, I daily drove it for years...Sounds like your tune is way off for the low compression...

  3. #3
    Join Date
    Mar 2019
    Location
    PA
    Posts
    15
    My Cars
    94 325i
    Quote Originally Posted by Substance D View Post
    I used to have a M50b25TU with .140mls...it was a dog down low, but it did drive fine, I daily drove it for years...Sounds like your tune is way off for the low compression...
    Were you on the stock tune?

  4. #4
    Join Date
    Jun 2012
    Location
    Socal
    Posts
    298
    My Cars
    turbo e36
    After the motor was rebuilt with the .140 I ran a red label 413 that had a chip in it, but it was not especially tuned for low comp. It ran fine clean, it just was slow.

    I think you have a tune related issue, or maybe forgot to hook up a sensor, doesn't sound like a mechanical issue to me. My 2c

  5. #5
    Join Date
    Apr 2006
    Location
    Minnesota eh?
    Posts
    6,155
    My Cars
    86 325es
    Some things that come to mind to check. Make sure the vanos solenoid and valve are moving freely. Take the valve cover off and double check the cam timing. Check for vacuum leaks such as a pinched or missing manifold gasket, injector O-ring, Idle valve connector, vacuum hoses, ect... Make sure the coil ground wire is hooked up to the front of the head. Check the connections at the sensors, particularly the MAF. Check the fuel pressure and vacuum hose going to the regulator.


    86 325es, 2.8L m50, S476sxe, ProEFI 128 ecu, e85, solid rear axle, TH400 trans, 28x10.5w slicks, zip ties, popsicle sticks, tape
    best time 9.06 @ 151.8 mph, best 60 foot 1.30

  6. #6
    Join Date
    Jun 2005
    Location
    New England
    Posts
    25,402
    My Cars
    F90 M5; E36 M3 Turbo
    I don’t think the lower compression is the issue. Could be the vanos is not working, you did not reassemble everything properly (could be a wiring or sensor issue or an air leak) or there an an issue with the tune and fuel injection hardware — might not be compatible.

  7. #7
    Join Date
    Mar 2019
    Location
    PA
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    My Cars
    94 325i
    Figured it out, I made a dumb mistake. When I was putting the intake elbow back on at 3:00am I somehow forgot to reconnect the ICV.

    Thanks for your help everyone.

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