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Choking, bucking, backfiring, and running rich

This is a discussion on Choking, bucking, backfiring, and running rich within the General Help forums, part of the LSx Technical Help Section category; Hey guys, have a bit of a problem. 2 years ago i had an LQ9 put in my car because ...

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    Unhappy Choking, bucking, backfiring, and running rich

    Hey guys, have a bit of a problem. 2 years ago i had an LQ9 put in my car because i blew up the LS1 that it came with. I used the long block and put the intake, belt driven accessories, and oilpan from the LS1 on the 6.0. I also got a pair of pacesetter longtubes and sent the ecu to frost to have him adjust it for the 6.0, edit out the emissions, and do some other adjustments. I put it all back together and it will not run for sh*t. it feels like it's running on 6 cylinders and when under any load or when i give it any gas at all you can hear it and feel it cut cyls. the more gas you give it, the more cyls it cuts out. it backfired through the intake the other day and through where the EGR block off is. lucky for me that the block off plate can only be attached on one side as it blew the other side off and put a hole in the fabric (heat shield?) that is attached under the hood instead of destroying the intake manifold. This car is getting combined city/highway 12 mpg and is literally pissing gas out of the exhaust onto the road to mark its territory. I was driving in the rain yesterday and something got wet and it cut down to what feels like 2 cylinders. the fastest i could get it up to was 15 mph. this has got to stop and i do not know where to start. I replaced coils, plugs, wires, and o2 sensors when the motor was swapped. people that i ask say that it is because of the computer tune but i think that they are wrong, it was doing this before i sent the ecu away and after i got it back it was not any better, except that the torque converter would lock up and it does not throw codes for the missing emissions components. all it has on it are long tube headers and i have not put an exhaust system on it yet because i want it to run like its supposed to first. Everyone i talk to tells me to do something different, or says its the computer (because they all run carbeurators and think that efi is FROM THE DEVIL!)
    On a side note, I went to jail about 15 months ago and just got out last wednesday. I put a new battery into it and 5 gals of premie and it cranked right over. go GM!
    Oh, when i disconnect the battery (i need to sometimes) and the ecu gets reset, when i go to start it, i have to give it a little gas to get going, like its not getting enough air. eventually it will idle down when i close the throttle little by little, and run. Do i need to widen the hole in the throttle body blade a little bit to give it more air for the slightly bigger displacement?
    If there is anything that I have left out please ask me. I just need to get it running without backfiring and choking. If there are any cheap things that might do it, tell me them first because I'm broke. I am very good at what i do, but nobody wants to give a felon a job

    Thank you, Matthew Wade

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    None Shall Pass Knight's Avatar
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    When you installed the longtubes, did you replace the O2s with the ones with the longer extensions? Or did you splice the wiring? When was the last time you cleaned the MAF? Have you checked all the plug wires at the plugs and coils to make sure they are all on?

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    Yes, I got the ones with the longer extensions, stock for a corvette i believe, but i cannot remember the model number. I got some MAF cleaner and a can of seafoam at oreilleys last week and used them both. I have checked the plug wires to make sure that they are connected at the plugs and at the coils. The last codes that it showed were the Random Multiple Misfire Code (and the ses light blinks sometimes) and now a code for a bad knock sensor is showing up.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Try disconnecting the MAF and see if it will idle better.

    If it does your MAF might have


    One more possibility....can you get a fuel pressure gauge and see what it's reading. There is a access port on the drivers side of the fuel rails, twist off the cap and attach the gauge. At idle you should have around 50-60 psi. Below 40 and something is wrong with the fuel pump or regulator.
    Last edited by SMWS6TA; 09-27-2012 at 12:40 PM.

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    I can do that, can i run it around the block like that? at idle it sounds kinda mean, but you cant really tell its cutting out like it does, really more under load, so id have to actually get on it. My neighbors are hating me with these open headers...

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    Spaz is My Mentor SMWS6TA's Avatar
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    no do not drive with it around the block, just see if the idle changes. Also I added some more to my previous post for you to read.

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    I thought it might have been the fuel pressure as well, or a pump going out. i borrowed the test kit from advance and when i turn the key to run it pumps up to the recommended pressure and does not leak down. when i start the car the needle on the test guage vibrates really fast. i dont know if its supposed to do that or not. one vibration for every revolution of the motor, or maybe one vibration for every revolution of the fuel pump, i dont know. do i need to start the car with it disconnected or disconnect it while the car is running and listen for differences? Thank you very much for your help

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    Spaz is My Mentor SMWS6TA's Avatar
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    not sure what you mean by vibrations, the needle should just point to a number. If it's too low then maybe that's why it's vibrating.

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    Ok, disconnected the maf with no noticable difference. when i hook up the fuel pressure test gauge, the needle points to a number (around 58 i believe) with the engine off and the key in the run position, but when i start the engine, the needle on the pressure gauge fluctuates from 50-58 really fast. i drove with the pressure gauge hooked up under the hood and the more load i put on the engine, the wider the pressure gauge needle fluctuates. Like it vibrates between 50 and 58, then when i drive down the road it vibrates from 48-58 or more depending on how far i press down on the gas.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Ok, good...

    Pressure readings are fine,

    I'm scratching my head now.....I saw you said you replaced the O2's, but did you connect them to the front O2 wire harness? It's an easy oversight.



    You said that the swap happen about 2 yrs ago, did it run right after the swap or was it causing issues right away? <<If not that did it just start having issues?

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    Thats a good question. It was not me that did it, I did not mean to be misleading, it was a shop and i suppose i just assumed that they did it the right way. I could check that, it might be tomorrow before i can, i need to find a series of pictures of where the front and rear hookups for the o2 sensors are. This means jacking up the car and crawling under it? it will have to be done after work. If thats all that needs to be done im going to be sick.

    Yes, it was done 2 years ago and no, it did not run right after the swap. the shop did a compression check on the cyls and said that the compression was spot on and they didnt know what else to do. after that i was pretty much on my own because i had already paid and their job was done and i wasnt going to give them any more money so there wasnt any incentive for them to get it running perfectly right... fast forward 2 years later and nothing has changed.

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    None Shall Pass Knight's Avatar
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    I agree with Scott. Start by making sure the connections are correct. You might also check the wiring to make sure it hasn't contacted the exhaust and melted.

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    Spaz is My Mentor SMWS6TA's Avatar
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    The front O2 harness is near the block, where the cats should be. Thr rear O2 harness sits about next to the tranny.

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    Take a look at the crank sensor also, could cause some of your symptoms.
    Are your gauges telling you anything else? Water temp working correctly?

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    I found a picture of the wiring harness on the internet and it looks like the o2 bank 1 sensor1 is right by the alternator wire, bank 2 sensor 1 is right by the CKP (crank position sensor?) and the oi level sensor. Thats interesting because my oil level light has been coming on and i know for a fact that the oil level is fine. The crank position sensor(if thats what that is) is right there and tatertot91 says that the sensor could cause some of those problems. Hmmm. the newer headers are longer then the stockers, and the harness is 14 years old. maybe the heat shielding on the harness does not extend far enough down the line to protect it from the heat of the new, longer pipes...
    Let me check this out after work tomorrow and get back to you. as i type it out it makes sense that all or some of those wires could be burnt or crossed.

    in a recent post on this thread i said that i had to disconnect my battery sometimes but i did not go into details as to why. I thought it was an unrelated incident but i have a small short somewhere and if i do not start the car to charge the battery every day, the battery goes dead, so dead that it cannot be charged back up (its not a deep cycle battery) and i have to take it back to walmart every couple months and get a new one. they have not caught on yet and im on about my 30th battery, lol. perhaps those wires are crossed? maybe a couple sets of crossed wires s causing all my problems?

    And to answer your question tatertot, yes, the gauges show up fine, takes this iron block a bit longer to heat up then the aluminum block and it does not run as hot, i was not used to that. oil press and speedo and rpm and all are fine.

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    Quote Originally Posted by draxxus 2.1 View Post
    I can do that, can i run it around the block like that? at idle it sounds kinda mean, but you cant really tell its cutting out like it does, really more under load, so id have to actually get on it. My neighbors are hating me with these open headers...
    If you are running open headers that will make the o2's read lean and dump in a bunch of fuel.

    Put on extensions or an exhaust.

    Brad
    Last edited by bmax327; 09-28-2012 at 12:26 PM. Reason: highlight quote
    1999 Formula, M6, mostly stock daily driver. ARH Headers, Hooker cat back, Koni's. EFI live V2, LC-1 serial connection. BRE custom cam

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    Do you know if all the ground wires are properly connected in the engine bay? That constant battery drain has me thinking.

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    all the grounds should be connected fine. I am going to check all that this weekend when i get under it to check out the wiring harness and the o2 sensors. It needs and exhaust and im planning on doing an x-pipe and then some bullet style mufflers with some turndowns before the rear axle, have the mufflers and the x pipe, but most of the exhaust shops around here say it cant be done no matter how many pictures i show them of others with the exact same configuration, and the one that will do it wants $300 to do just that. It feels like everything is against me getting this fixed... except you guys. I was going to crawl under it today but it was raining and then there was BBQ on the river and this cutie wanting to go down there with me... I need to do it asap, but tomorrow i have to work in the am.

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    If it sat for 15 mos the injectors may be clogged, get a little heavy of the fuel injector cleaner if you can't afford to have them cleaned. That would also account for the heavy fuel problem. Try to drive it easy light throttle for a while to clear the injectors but really they may never get totally well again. The wet driving problems indicate bad practices for plug wires and other wiring -try to dry all out and check everything again, looking for sparks to ground -look under the hood in the dark for sparks although you might not see any. Check for the basics first.

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    Quote Originally Posted by bmax327 View Post
    If you are running open headers that will make the o2's read lean and dump in a bunch of fuel.

    Put on extensions or an exhaust.

    Brad
    This is hugely correct! You CANNOT run open headers with front O2s. You can disconnect them (and unhook the batt to clear the learning) and then run open headers, but you cannot run the car with them and headers as well. If you have done this at all, certainly swap plugs as well because what you have will be soaked and fouled.

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