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Possible vacuum leak?

This is a discussion on Possible vacuum leak? within the General Help forums, part of the LSx Technical Help Section category; I just test fired my LS1 swap in my BMW last night. It fired right up but then died almost ...

  1. #1
    M3+LS1=Badass
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    Possible vacuum leak?

    I just test fired my LS1 swap in my BMW last night. It fired right up but then died almost immediately. I installed a MS3 cam and Patriot heads with upgraded pushrods before I dropped it in.

    I am missing a few sensors like the coolant temp (to the dash), air charge sensor, and o2 sensors. I plugged the EGR, charcoal vent solenoid, and brake booster because I don't need them.

    My question is, will the car run without any of the above mentioned sensors, and if so, does my problem sound like a vacuum leak? I don't know if it's because of a leak, missing sensors, no PCM tune, or a combo of the three.


    Any help will be greatly appreciated. Thanks in advance guys

  2. #2
    Moderator Cutlass's Avatar
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    No MAF sensor or PCM tune can do that. It could also be the VATS security system

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    M3+LS1=Badass
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    Quote Originally Posted by Cutlass View Post
    No MAF sensor or PCM tune can do that. It could also be the VATS security system
    Are you saying that neither the MAF or a bad tune could cause that? And if so, does that mean it's more towards a vacuum leak then?

    Also, whats the VATS security system, and what can I do to check/fix it?

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    Moderator Cutlass's Avatar
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    No sorry. I meant not having a MAF or tune can cause problems.
    VATs: How to Bypass your VATS

  5. #5
    M3+LS1=Badass
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    Oh ok. I just tried to fire it again, but this time when it started the revs jumped to like 1.5-2k so fast that I got scarred and shut it down right away (MS3 cam, LS6 heads, and open headers = I bout shit myself)

    I thought it was a fluke so I did it again, and again the revs shot straight to 1.5-2k so again I shut it down. My neighbor then proceeded to yell at me lol. Is it normal for a cold engine with this big of a cam to start and rev so high like that? I couldn't let it run long enough to see if the revs would come down out of fear that something might be wrong, and also the cops would have been here

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    I know for a fact that if your Water temp sensor is messed up it will definately cause you all kinda A/F ratio problems. My last bad one made the cpu think it was about -30 degrees below and it got so bad it didn't even want to start until I replaced it.

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    M3+LS1=Badass
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    I guess it'll be easier to diagnose once the sensors are in, but it's taking ups for ever to get here

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    you will definitely need the coolant temp and IAT sensors. I suspect that car won't run very well at all with that cam and no tune. With the revs shooting up like that I suspect something is going on somewhere with the airflow or throttle body. Get the sensors in there and button everything down before going any further. No sense in trouble shooting a motor that's not complete....just a guessing game.

  9. #9
    LSwut tep98ws6's Avatar
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    need inputs for the outputs
    your build is really neat though, i'm excited to see your finished build

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    M3+LS1=Badass
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    Well I found out that the VATS is still enabled, so that's definitely part of it, but yeah, I'm just going to get it all together, tow it to a shop, and have them use HP Tuners to disable VATS and get it running smooth.

    By the way, if it is a vacuum leak, how do you check? Just listen for air, or use some sort vapor dye?

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    Moderator Cutlass's Avatar
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    It doesn't seem like a vacuum leak problem at this point.

  12. #12
    LSwut tep98ws6's Avatar
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    Quote Originally Posted by shaggsm3ls1 View Post
    Well I found out that the VATS is still enabled, so that's definitely part of it, but yeah, I'm just going to get it all together, tow it to a shop, and have them use HP Tuners to disable VATS and get it running smooth.

    By the way, if it is a vacuum leak, how do you check? Just listen for air, or use some sort vapor dye?
    Like Cutlass said, probs not a vacuum leak, but to test a vacuum leak - rig up a smoke machine and just watch for the leaks

    http://chemistry.about.com/od/howthi...kemachines.htm

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