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Possible closed loop issues

This is a discussion on Possible closed loop issues within the General Help forums, part of the LSx Technical Help Section category; I finally got my exhaust sealed up and fixed and I am going for a tune on wednesday and I ...

  1. #1
    Member bryceslu's Avatar
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    Possible closed loop issues

    I finally got my exhaust sealed up and fixed and I am going for a tune on wednesday and I have something I want to see If I can iron out beforehand.

    The exhaust pressure coming out of the pass side exhaust it noticeably weaker than the driver side (I am running true duals and no mufflers so there is no blockage). I originally thought I might be down a cylinder or actually random firing on a cylinder, as I had issues with 1 coil after putting the headers on basically firing when it wanted to.

    I thought I got that fixed and I pulled the wire and put in a plug and it seemed to be firing fine comparable to another coil. Weird thing is that there is no code being thrown for a misfire. also the car doesnt feel like it has the power it should.

    Now today I noticed that at cold startup both sides were equal as far as pressure. But as it warmed up, and I am assuming hitting closed loop, the pass side is noticeably weaker.

    Is there anything i can look into before my tune so we dont hit a wall?

    I pulled the front plug on pass side (the 1 i had coil trouble with a while back,I have since changed the plugs and they only have 100 miles on them) and it was darker than the other one I pulled. So it would seem that its not firing properly for some reason.

    Again weird part being that its only when the car warms up does this happen.

    Any suggestions on places to start troubleshooting before I waste time for the tune?

    Thanks in advance.
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    Veteran 0rion's Avatar
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    do you have an x-pipe?

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    Member bryceslu's Avatar
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    Quote Originally Posted by 0rion View Post
    do you have an x-pipe?
    nope, just straight duals out the back. each side is seperate pipe.

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    Your dealership guy konigandy6's Avatar
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    Quote Originally Posted by bryceslu View Post
    nope, just straight duals out the back. each side is seperate pipe.
    I was always told you want equal pressure on both pipes, that's why people run H/X pipes.

    I can't answer why it's that uneven though... Compression on one cylinder on that bank? Not sure.

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    Member bryceslu's Avatar
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    Quote Originally Posted by konigandy6 View Post
    I was always told you want equal pressure on both pipes, that's why people run H/X pipes.

    I can't answer why it's that uneven though... Compression on one cylinder on that bank? Not sure.
    Yeah its really aggravating me lol.

    I guess I will see what the tuner pulls from datalogging and go from there. I just hope it doesnt create a roadblock and we cant tune it as there is a problem somewhere.

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    Electrical Engineer KMdef9's Avatar
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    Quote Originally Posted by konigandy6 View Post
    I was always told you want equal pressure on both pipes, that's why people run H/X pipe.
    I have heard this as well. With this, there is always going to be alittle bit of a difference if pressure from one side to the next. How much a difference is there?

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    Member bryceslu's Avatar
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    Quote Originally Posted by KMdef9 View Post
    I have heard this as well. With this, there is always going to be alittle bit of a difference if pressure from one side to the next. How much a difference is there?
    Well as i said at cold start it is the same. after it warms up its definitly noticeable...kind of hard to explain the difference in feel... if i had to guesss, the pass side feels the same 1 in away from the pipe compared to about 8 inches on the driver side away from the pipe.

    The more I think about it the more it seems like its probably not an issue. I hope the tune will either fix this or at least tell me why. I wouldnt be as concerned if it didnt feel the same at cold but different when warm.

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    Electrical Engineer KMdef9's Avatar
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    Quote Originally Posted by bryceslu View Post
    Well as i said at cold start it is the same. after it warms up its definitly noticeable...kind of hard to explain the difference in feel... if i had to guesss, the pass side feels the same 1 in away from the pipe compared to about 8 inches on the driver side away from the pipe.

    The more I think about it the more it seems like its probably not an issue. I hope the tune will either fix this or at least tell me why. I wouldnt be as concerned if it didnt feel the same at cold but different when warm.
    Are both pipes, from the headers, the excact same length with the excact same bends at the same angles?

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    Quote Originally Posted by KMdef9 View Post
    Are both pipes, from the headers, the excact same length with the excact same bends at the same angles?
    cant be.

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    Member bryceslu's Avatar
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    Quote Originally Posted by KMdef9 View Post
    Are both pipes, from the headers, the excact same length with the excact same bends at the same angles?
    pretty darn close. where the pass side would normally be shorter, its actually crossed over after the axle, behind the back bumper, and run out the driver side exit in the bumper.

    Im assuming the person who did the duals did so in order to keep the pipes closer to the same length instead of having the driver side being longer.

  11. #11
    Electrical Engineer KMdef9's Avatar
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    Quote Originally Posted by bryceslu View Post
    pretty darn close. where the pass side would normally be shorter, its actually crossed over after the axle, behind the back bumper, and run out the driver side exit in the bumper.

    Im assuming the person who did the duals did so in order to keep the pipes closer to the same length instead of having the driver side being longer.
    The passenger side has an extra turn it or 2 in it? sounds like a couple of 90 degree turns (2 45's to get over the axel)

    This will obviously slow down the flow compared the driverside, I'm not sure it would slow it down as much as you a feeling, but the actual pressure might be in the range of "normal opertation." I'm not sure how much difference in pressure there is in "normal operation." And since I'm no tuning expert either, I think it's possible with a good tune the flows should be balanced out. It's hard to say, as most people I know with true dual exhaust have a X or H pipe. Your tuner might be able to answer those questions as well before you actually get the tune done.

    From my understanding you ideally want the same flow (backpressure) with your exhuast. It may be affecting your overall performace having them mismatched. But, all my expereince with exhaust true duals has been with and x or y pipe.

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    Member bryceslu's Avatar
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    Quote Originally Posted by KMdef9 View Post
    The passenger side has an extra turn it or 2 in it? sounds like a couple of 90 degree turns (2 45's to get over the axel)

    This will obviously slow down the flow compared the driverside, I'm not sure it would slow it down as much as you a feeling, but the actual pressure might be in the range of "normal opertation." I'm not sure how much difference in pressure there is in "normal operation." And since I'm no tuning expert either, I think it's possible with a good tune the flows should be balanced out. It's hard to say, as most people I know with true dual exhaust have a X or H pipe. Your tuner might be able to answer those questions as well before you actually get the tune done.

    From my understanding you ideally want the same flow (backpressure) with your exhuast. It may be affecting your overall performace having them mismatched. But, all my expereince with exhaust true duals has been with and x or y pipe.
    Yeah I hear ya....it really is boggling, and concerns me, as at a cold start or open loop both sides seem equal in pressure. then after warming up, my guess going to closed loop, the pass side drops off quite a bit as compared to driver side.

    And yes at the rear there are a couple extra 45 turns for pass side but with it just running through open pipe it shouldnt cut down the pressure that much. also wouldnt make sense that it matches the driver side at cold idle.

    I am really hoping the tune will help or at least reassure me that it is no big deal.
    My concern though was that if it was happening when going to closed loop is that it then uses different inputs from the car to adjust vs open loop. Might be an o2 sensor i guess, but i would think a code would be thrown for that.

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