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Thread: Stock LQ4 emmissions fail need some help

  1. 10-28-2020 #1
    FixxerAutomotive
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    Stock LQ4 emmissions fail need some help

    Hello,
    So i have a 2005 LQ4, LS1 intake, Small delphi (truck) fuel injectors- using adapters, 98 vette filter/regulator, 3 wire MAF, all stock internals, long tube headers dumping into single 3" flowmaster cat. Im using a 2000 silverado base tune that i tuned for the 3 wire MAF and non-vacuum referenced fuel pressure regulator. I got the MAF table from a 2000 LS1 tune, and the IFR table from a 2005 Tahoe. Anyways, the car runs great with no issues... I went to get an emmissions test last year and got the guy to test it without catalytic converters. It passed the high RPM test fine =, but the idle was too dirty. I had 600ppm HC with a max of 200. So this year, i got the flow master cat and bolted on there thinking that would fix my problem. this time the HC was 880 with the cat on. So the test was much worse with a cat vs without... hmmmm My long term fuel trims are -1.56 on both banks and short term is plus or minus 5. So my question is, did i screw up on the tune somewhere or is there something else i am missing? I currently am running ethanol free premium gas, do you think i should dump E85 in and retry? Do i need to change the tune and injectors to do so? I think i can get some Flex fuel injectors cheap... Any help would be much appreciated. The guy who tested it said he thought that the cat isn't broke in yet- i literally unboxed it bolted it on and drove to the test station...
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  2. 10-28-2020 #2
    5FDP
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    Post up your tune and a log file.

    You could try changes to idle rpm and timing to maybe help. I would also try to get that cat as hot as possible before going to the test station too.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.
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  3. 10-29-2020 #3
    FixxerAutomotive
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    Thanks 5FDP,
    Thats a good idea. I took my 1990 ZR1 down to be tested today and noticed that it idles just above 1000rpm (versus 650rpm on the LQ4). Maybe they used to have the idle set higher in the old days to pass the sniff test... I'm going to burn that cat in real good and bump the idle up and see what happens. If that doesn't work, then maybe ill add a smog pump. then if all that doesn't work, ill try using the E85 and see what happens. Ill post back and let you know
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