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Thread: Trouble Passing Emissions

  1. #1
    Join Date
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    Trouble Passing Emissions

    Hi guys, I'm having trouble posting to tccoa, so I thought I would pick your brains while I wait for my account to be fixed.

    Took my 93 5.0 LX in for emissions today and failed miserably.

    Background on the car:
    Engine - stock except for 94 cobra intake
    Transmission - swapped for m5r2
    Computer - tuned by Dave Dalke after all modifications were made. Thermactor and Egr deleted.

    Exhaust - scp downtubes with cats. Tru-bendz 2.25" true dual.

    I passed with the same mods last time without much issue. I'm not sure what's up? No codes. I can view the o2 status on the diagnostic mode of the vmm and it switches back and forth from rich/lean actively while idling. It smells a bit rich though. Milage is about the same as always.

    Any ideas are appreciated.

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  2. #2
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    How many miles on the cats now? Are they full boat or mini/hi-flow?

    If you're interested in a primer... https://www.youtube.com/watch?v=4st6Hf5-nJ4

    I think if you focus on correcting the high HC, there is a chance the other two will fall in line.

  3. #3
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    High HC lead me to think either Vacuum leak or bad O2 sensor though FPR is possible. I've had O2 sensors fail within range and not through code.

  4. #4
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    Quote Originally Posted by KMT View Post
    How many miles on the cats now? Are they full boat or mini/hi-flow?

    If you're interested in a primer... https://www.youtube.com/watch?v=4st6Hf5-nJ4

    I think if you focus on correcting the high HC, there is a chance the other two will fall in line.
    Around 10,000 on the cats since install. They are magnaflow, high flow but still oe style ceramic catalyst.

    Quote Originally Posted by bowez View Post
    High HC lead me to think either Vacuum leak or bad O2 sensor though FPR is possible. I've had O2 sensors fail within range and not through code.
    O2's also have around 10,000 and are motorcrafts. It might be a place to start. I'm sure there are no vacuum leaks, but wouldn't that lean it out? It smells rich.

  5. #5
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    Quote Originally Posted by TBirdJKC View Post
    Around 10,000 on the cats since install. They are magnaflow, high flow but still oe style ceramic catalyst.



    O2's also have around 10,000 and are motorcrafts. It might be a place to start. I'm sure there are no vacuum leaks, but wouldn't that lean it out? It smells rich.
    With results like that, I'd start by pulling codes. You've got something obvious wrong, like O2s not plugged in somewhere, to fail on all 3 categories... and yeah, look at the FPR first off if you're smelling gas. Also, since you eliminated EGR, you would need to pick up the slack using 3way cats.
    Last edited by TbirdSCFan; 05-02-2017 at 09:59 PM.

  6. #6
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    Quote Originally Posted by TbirdSCFan View Post
    With results like that, I'd start by pulling codes. You've got something obvious wrong, like O2s not plugged in somewhere, to fail on all 3 categories... and yeah, look at the FPR first off if you're smelling gas. Also, since you eliminated EGR, you would need to pick up the slack using 3way cats.
    No codes present. The cats are 3 way. I made sure of that before deleting the thermactor. FPR is a good idea. I'll check that out tomorrow and see if I smell any gas around the vac line. Maybe the o2's are toasted. I thought maybe I had a leaky injector but it passed a cylinder balance test.

  7. #7
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    With the HCs and CO that high, you are definitely running way rich. Running rich though usually lowers NOx, and that is also way high, so you may have more than one problem here, but regardless, you have to fix the rich condition first. If you have access to a scan tool, read the long-term and short-term fuel trims to see if the computer is adding fuel or taking it away. If the O2 sensor is bad and telling the ECM that it is running lean, then the ECM will compensate by raising the fuel trims to try to add fuel. On the other hand, if there is some mechanical problem causing it to run very rich, like a bad FPR, or a pinched fuel return line, or leaking injector, or something like that, then the O2 sensors would tell the ECM it is running rich, and the ECM will compensate by lowering the fuel trims to try to take away fuel to bring it back in spec. Once you get the air/fuel ratio dialed in, the HC and CO numbers should clear up, but based on those NOx numbers, I suspect you may have also fried your cats from running so rich. Even with 3-way cats, passing the NOx without EGR can be difficult. Dialing back the ignition timing will help some with that, as will running it a bich richer, but those things also raise the HC and CO numbers, so it becomes a balancing act to get all 3 numbers below the requirement.

  8. #8
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    Well I checked the FPR. No fuel smell around the vacuum line. And I hooked up my pressure gauge and it falls into the specs outlined by the FSM. Looking more like a bad O2. I put a pair on order this afternoon. We shall see. Thanks for the help so far guys. I'll report back after I run it through emissions testing again.

  9. #9
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    Well. Just a little update. I went to fire it up this morning and it was flooded. I must have a leaking injector.

    I was hoping it would be easier to pass emissions with a relatively stock engine, but I rather not spend the money on new stock Injectors, since I'm upgrading everything very soon for a turbo.

  10. #10
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    As long as the tune is correct, larger injectors (within reason) won't have any adverse effect on the emissions.

  11. #11
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    Quote Originally Posted by MadMikeyL View Post
    As long as the tune is correct, larger injectors (within reason) won't have any adverse effect on the emissions.
    I should be ok. Upgrading under the guidance of David Dalke, followed by a dyno tune at SCUI. I figured it would be less trouble to get it passed now with the car still mostly stock, especially since it will qualify for antique plates next year. I wont have to worry about emissions testing after that.

  12. #12
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    go head and toss some siemens deka 80s on it and get dave to put the info in your tune, you shouldn't have a problem passing emissions after that

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