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Misfireing, Throwing Codes, HELP

This is a discussion on Misfireing, Throwing Codes, HELP within the General Help forums, part of the LSx Technical Help Section category; Originally Posted by JunkyardZ Have you checked fuel pressure and volume yet? Are you saying that number 6 had the ...

  1. #21
    Member Goldcuffs's Avatar
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    Quote Originally Posted by JunkyardZ View Post
    Have you checked fuel pressure and volume yet?
    Are you saying that number 6 had the most misfires? I've had a handful of instances where only one cylinder was the culprit but it was throwing random misfire codes. For example, had a honda odyssey come in idling very rough but saw no power loss while driving and seemed smooth while revving. Seemed almost like the egr was stuck open. Ended up being a bad #1 coil but the scanner was showing misfires on multiple cylinders. Get a good spark tester on the #6 coil and make sure it can jump a big gap all the time. Having said that though, I have never seen a GM ls series coil go bad and we used to work for a van fleet running 03 and up 6.0 liters with 200k to 300k miles on their vans.
    Fuel related: Chevy Tahoe that idled fine and under no load ran great. On the test drive though it would totally lose power and throw lean codes. Checking fuel pressure pointed to a bad fuel pump.
    Anyway, sorry for getting lengthy, just want to help. Intermittent problems can make you pull your hair out.
    +1. I have also had the cylinder before or after in the firing order be the culprit but it flags the wrong one. And as you said those coil packs are pretty tough. The fuel pumps on these cars are the weakest link as far as I'm concerned (GM products period for that matter) I've changed pumps in trucks with as low as 20k on them.
    Last edited by Goldcuffs; 12-26-2009 at 07:47 AM. Reason: spelling

  2. #22
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    Quote Originally Posted by Goldcuffs View Post
    If you rev it a few times and it stops doing it you could have an injector bleeding down filling the cylinder with fuel. Does it only do it cold or can you turn it off after you clear it out and get it to do it again right away? I've never had a regulator cause a misfire. Not that it won't happen, but you would more than likely get a lean or rich code instead.
    It does not do it when cold, i will crank it in the morning, and it will run fine, then drive it some, and if i start it warm, it will misfire, and after i clear it up again i can park it for like 5 mins, come back crank and it will be doing it again, and it will go away after i rev some. But doesn't come back till i re crank.
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    This sounds almost identical to what mine was doing. I found that both upstream O2 sensors were pretty lazy, and it was throwing my fuel trims out of whack. I was skeptical because they were both Delco sensors with 30,000km on them. Needless to say, I bought a different brand. I bought a couple NTKs from NAPA. They work great, solved my problem. Bad O2 sensors can cause all sorts of strange problems.

  4. #24
    Junior Member blworden's Avatar
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    I had a similar experience a few years back (Cant remember the codes) it ended up being my LS1 PCV Hose System. I had a crack by the connector just under the mass air flow sensor unit. GM told me they had made a revision to this in 2001 or 2002 because of the mass failure rates due to the material becoming brittle.

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    Update: After doing a 600+ mile trip, it went away. Now it only does it in rain..


    Hmmmmmmmmm

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    Quote Originally Posted by Sarge91 View Post
    Update: After doing a 600+ mile trip, it went away. Now it only does it in rain..


    Hmmmmmmmmm
    Probably o2 sensors getting wet. That will surely cause a mis fire condition.

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    Well here is a new update..

    1 week ago i drove another 700 mile trip with the car, the car ran great the whole time, never missed a bit till i came back home and straight off the interstate to get gas, and after i filled up it started to miss, and i had just done 2 days of driving with NO problems.

    I put my MSD wires on, and i checked my plugs while i did that, every plug seemed fine. I compressed air all the coil senor connections, and look for any thing that looked off, but nothing.

    I took it and got a misfire reading, i had real bad ones all over the board when i actually got it to misfire, cause like i said, sometimes "rarely" it wont misfire. So at that time cyc 1 was missing the worse, so i went and bought a direct replacement coil pack. Swapped it and still was misfiring like before..

    And my last scan i got misfire on cyc 2,4,6,8 only.. so wtf..

    Its so random no shop can figure it out. Ive email my tuner to see what my fuel trims are and my air/fuel ratio.

    If it was injectors, it wouldn't be so random correct?

    And what about the fuel pressure regulator? How do you check it. And Would a bad one cause this?

    Thanks.

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    Do you get gas at the same station in your town? I ask because you said it didn't do this on your long trip, were you would be getting gas at other stations. Bad gas? Why is it not mis firing when your on trips? Bad gas?

    Have you checked fuel pressure yet? I saw it mentioned earlier, but didn't see you answer.
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    Well i pretty much use shell gas, and the station i filled up is the one i have been using every time i come back home from up north. I have been through probably 20 full tanks since it has started and maybe 3 of them has been non shell.

    No i haven't checked my fuel pressure, how is that done? Scanner?

    And and i do remember now, it did do it once upstate when i stopped and filled up also, started right as i cranked up. And that was 200 miles from my house.
    Last edited by Sarge91; 01-20-2010 at 02:48 PM.

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    Quote Originally Posted by Sarge91 View Post
    Well i pretty much use shell gas, and the station i filled up is the one i have been using every time i come back home from up north. I have been through probably 20 full tanks since it has started and maybe 3 of them has been non shell.

    No i haven't checked my fuel pressure, how is that done? Scanner?
    Installing a gauge on the end of your fuel rail. Drivers side. Has a schrader valve inside, hook the gauge up there. For pictures, check out my Sig, under "Install Gauges". Some pictures there.

    You do not need that gauge. Just a cheap FP mechanical gauge.

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    Quote Originally Posted by Hi-Po View Post
    Installing a gauge on the end of your fuel rail. Drivers side. Has a schrader valve inside, hook the gauge up there. For pictures, check out my Sig, under "Install Gauges". Some pictures there.

    You do not need that gauge. Just a cheap FP mechanical gauge.
    Ok, well i do have a nitrous plate, so no valve, and i also check for leaky nitrous and fuel silinones, but there fine. I may unhook it just to put a gauge up to it and see.

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    I mentioned this earlier in the blog but no one replied back on it...
    I said has anyone thought about there being to much ethenol in the gas, the ethenol breaks down and causes condensation in the tanks there for water is now in the gas some gas stations might have higher ethenol levels and it might have sat to long if your car misfires go get a bottle of stabilizer from advance auto (its red) and watch your car stop missfiring!!!

    you can still get gas without ethenol in it from boat marinas because boat motors cant handle the mix so if you want to test the theory make sure all the old gas is out and then get gas from a marina and see if your car stops missfiring and if it dont then i would continue to test everything else!!!

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    Ill try that 2fast4u.

    Anyways it got to a point where i couldn't stand it. Took it to a buddy, we hooked it up to a gm scanner, as usual everything seemed fine. We tested fuel pressure, it was great. Then we decided to swap the plugs once more. So put in all new plugs. It went away. It ran great for a week, then today it came back.. .. So im at a major lost here. Maybe something in my tune? Computer is messing up? Its just so random no one can pin point it. Ive done coil pack. Plug, plug wire. And all the other crap i said a few pages back..

    Where are the grounds located at for the computer, Injectors? Maybe there loose? All ground that i can see in the engine bay are tight and clean..

    Ill paypal 10 bucks to who can figure it out. lol

    Thanks

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    Senior Member Orcus79's Avatar
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    My guess is try running chevron 91 or what ever the premuim grade is in your area. I found that my 02 WS6 does not like shell one bit for gas. Dunno why. but ran great on Esso (might be Exxon in the US) and even better on Chevron.

    When you pulled the plugs what did they look like?

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    Quote Originally Posted by Orcus79 View Post
    My guess is try running chevron 91 or what ever the premuim grade is in your area. I found that my 02 WS6 does not like shell one bit for gas. Dunno why. but ran great on Esso (might be Exxon in the US) and even better on Chevron.

    When you pulled the plugs what did they look like?
    Well i have been running shell 93 since ive had it "2 years" and i filled up today with a different brand gas. We will see. Only thing i have around here for gas is shell, BP, or Pride.. I like chevron, but so far away..

    Here are pics, they looked fine..

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    Senior Member Orcus79's Avatar
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    with the out of focus pics it is hard to tell. but my guess is that you are a tad on the rich side, or it may be possible that the plugs are too cold.

    For now I would say, try new gas and run some cleaner through the system, then try going back to a stock temp and gap plug. Beyond that I don't know any more off the top of my head. More may come to me as the issue is worked on.

    Any details you could give about when it started, was there any work done on the car before it started?

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    ^

    Just the nitrous plate, but was on 2 month and 3 bottles before this happened.

    Yes the car runs rich. And the plugs are colder, Tr6s gaped @ .035 for the nitrous.

    But the weirdest thing is, i had that same tank of gas when i put new plugs in '1 week ago' from when it started to mis. And today it did not mis one bit.. Thats how random it is.

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    Senior Member Orcus79's Avatar
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    hmm, starting to wonder if you don't have a vacuum leak some where. From what little I know the gap and plugs are right for the spray.

    This is some what of a crazy idea, but pop the connections off the computer and have look at those for corrosion. Give all your connections a once over.

    One more thing I can think of is if you can, try to have a look at your cam position sensor and knock sensors. For the knock sensors you will have to remove the intake though. The reason I say knock sensors, is that I think and I am only guessing, is that they may also be used to sense missfires. but I am not certain.

    Just remebered on more thing, check the crank sensor as well I think that used to trigger the firing of the plugs.

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    Quote Originally Posted by Orcus79 View Post

    This is some what of a crazy idea, but pop the connections off the computer and have look at those for corrosion. Give all your connections a once over.

    One more thing I can think of is if you can, try to have a look at your cam position sensor and knock sensors. For the knock sensors you will have to remove the intake though. The reason I say knock sensors, is that I think and I am only guessing, is that they may also be used to sense missfires. but I am not certain.

    Just remebered on more thing, check the crank sensor as well I think that used to trigger the firing of the plugs.
    First, are the connections the one on the side of the grey box? "Computer"

    And ive checked the MAP and cam position sensor via scanner, and the knock sensor wasn't activating.

    And ill recheck bc i dont recall seeing a crank senor.

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    Senior Member Orcus79's Avatar
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    Yeap, on the passenger side of the engine bay under the cowel is what you are looking for..

    The crank sensor is located behind the starter. Though reading the manual, if you remove it there you have to a special relearn procedure for it and you need a scan tool. that can activate it, unless one of the more knowledgable members knows something better.

    Oi the more I read into this the more ideas I get, have you watched your temps on the scanner while you had it connected and it was miss firing?

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