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Thread: Annual Emmisions Test - Help

  1. #1
    Fuel Injected! Terminal_Crazy's Avatar
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    Annual Emmisions Test - Help

    OK guys just failed the annual emmission test.

    Initail tune was way off being based on the wideband and what the car wants.

    Limits are
    CO % 0.300
    HC ppm 200
    Lamda 0.97-1.030

    Initial test HC was in the 7-800 range lambda was around 1.15


    I reflashed with last years bin & with steveo's EEHack (increased timing & Idle speed) managed
    CO % 0.00
    HC 100-150
    Lambda eventually came down to 1.034 so F'in close.

    A big part of the issue is the 2x3" tail pipes although covering one up raised the lambda back over 1.11.

    I'm pretty certain there are no leaks on the pipes, even the cutout has been blanked off.

    What should i play with in the tune. It got better as the o2's heated up so fan temps will be raised.

    Any other suggestions please.

    Cheers
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  2. #2
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    Your tests appear to show the engine running slightly lean. Does your vehicle use catalytic converters? Could you post all three measured values for the initial test?

  3. #3
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by 1project2many View Post
    Your tests appear to show the engine running slightly lean. Does your vehicle use catalytic converters? Could you post all three measured values for the initial test?
    Yes it has a cat.

    The current tune has been with a wideband as the car drives so much better. I basically just switched closed loop back on and adjusted the BLM's back.

    What's strange is the lambda was way over even though i thought i'd be rich and the HC were 7-800.

    initially
    CO ?? can't remember but it was the first to pass.
    HC 7-800
    L 1.11 - 1.14


    I switched back to the tune from last year and bump timing up & rpm's to about 1200

    That dropped to about
    CO not much dropped 0
    HC 250 dropped to 132
    L 1.11 dropped to 1.04

    as I raised the rpm & timing the figures dropped.
    As it warmed up the igures dropped some more.
    As he covered one of the tail pipes the lambda actually dropped down to about 1.05 ish
    best reading on test was 1.04

    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  4. #4
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    The converter could be thought of as it's own engine. As such it is powered by fuel (HC and CO) in the exhaust as it reacts with any oxygen exiting the engine. With too much or too little of either the "engine" of the cat struggles to run.

    Fuel and oxygen start reacting in the combustion chamber and will continue reacting as the gas is pushed into the exhaust manifold and into the exhaust pipe. As the exhaust cools and the amount of inert CO2 increase the reaction slows. When you advance ignition timing you give fuel and air more time to react in the engine before it is forced out the exhaust. The reaction spends more time in the cylinder and around the heated exhaust valve and continues longer. More reaction time means there is less fuel and less O2 being dumped down the pipes. Less fuel and O2 means less for the "engine" that is the converter.

    It may seem counterintuitive, but retarding timing some on a system with cats can help clean up tailpipe emissions. While the exhaust from the engine may be "cleaner," having lower O2, CO and HC readings, it also does less to keep the cat warm which can ultimately result in the cat failing to cause the gases to react before they are measured at the tailpipe. The apparent lean reading, generated through WBO2 tuning, also suggests that timing is a bit on the advanced side.

    Increasing engine rpm cleans up emissions for several reasons. Among others, the increased volume of exhaust gas carries greater heat energy to the cat which helps the cat to react the remaining combustibles in the exhaust. Increasing idle speed while increasing spark advance is somewhat counterproductive because, although you add more heat, you are reducing the components that the cat reacts and increasing the components which cannot react.

    The easiest way I can think of to check the effectiveness of decreasing advance on emissions is to check converter temp before and after the change. If you're seeing temperature around 200 - 325 C (400 - 600F) the cat is barely above the "light off" temperature. If temperature as 650 to 700 C (1200 - 1400F) the cat is working vigourously and tailpipe HC and CO should be fairly low. If you see temperature approaching 1100 C (2000F) the cat is in danger of meltdown.

    Ultimately what you are doing is trying to balance engine efficiency with the catalytic converter's ability to burn fuel. For your combination you may have found the point where the engine burns fuel so well the converter is unable to do its job effectively.

  5. #5
    Fuel Injected! Terminal_Crazy's Avatar
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    Wow, what a brilliant explanation.
    That all makes sense and i don't think the cat has ever been that hot.
    I will have a play tomorrow and see what results i get.

    Thankyou
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  6. #6
    Fuel Injected! Terminal_Crazy's Avatar
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    Follw up

    OK
    I found a pinhole leak on the cutout Y so filled that with HT silicone for now.
    The cutout has a little bypass/bleed hole by the shaft so swapped my blanking plate in before the cutout.
    I've blanked one tail pipe with a bean can. The reversions would suck the can in and out of the tail pipe which i think will make the most difference.
    on the previous bin CAT temp was around 120.
    The car has only been idling today, initially for about 20 mins.

    I raised the fan on temps back to stock so it's idling around 105 degrees.
    Closed Throttle Timing i dropped back to stock values & raised idle speed.
    It's actually quite sweet.

    Idle speed 1100
    Timing around 27.
    MAP has dropped slightly
    CAT temps only reach 250 - 340 C front to back (2-3 times higher than before ), a decent drive will hopefully raise this.
    On the last test the car did sit for half an hour after driving there.

    I dropped timing to 20 but that didn't seem to affect the cat temp any. 27 seems OK for now.
    The Inj PW increased.
    37 1.7x
    27 1.9x
    19 2.1x
    so it is using more fuel than before.

    I also measured the temp of the tail pipe at around 105 and that also is noticably hotter and doesn't smell.

    BLM's were sitting at 132 132

    Wideband is averaging 15.1 rather than 15.2 and seems more stable than before. It used to bounce 14.8 -15.8 where now it reads 14.7-15.3


    Results looking good so far.
    Any other suggestions I can try before retesting?


    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  7. #7
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    I think you're on the right track for this test. If the test only looks at HC, CO, and Lambda it sounds like you should see favorable results. Don't let out the secret of the DIY "sniffer" test. Although it isn't an expensive or complex diagnostic tool, I've used it myself in a pinch.

    You might want to reconsider converter position or exhaust pipe configuration before your next test. You may be able to return to your previous timing settings to improve mileage if you can get more engine heat to the converter. Many newer vehicles position the converter immediately after the manifold. This maximizes heat at the converter. I've seen custom systems built which place a pipe inside a pipe to reduce heat loss. Maybe this is why some GM trucks have a similar configuration on the Y pipe pre-cat.

  8. #8
    Fuel Injected! Terminal_Crazy's Avatar
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    The test is only CO HC & Lambda.
    The converter is in the stock LT1 position but i have MAC midlength headers on.
    There isn't really any room to move the cat & it only needs to be on so i can pass.
    I did have a decat pipe I could swap but found the exhaust cutout a much better option.

    Something i have just read suggests that the fuel i'm using, BP ultimate unleaded has a stoich value nearer 14.46.
    The base unleaded is nearer 14.7.
    How/would this affect stoich and the wideband AFR guage reading lean?

    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  9. #9
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    Quote Originally Posted by 1project2many View Post
    I've seen custom systems built which place a pipe inside a pipe to reduce heat loss. Maybe this is why some GM trucks have a similar configuration on the Y pipe pre-cat.
    at the very least, on 1st/1.5 generation W cars with 3100s, this happened at the factory as well. the downpipe looks to be in the 2.25" range, but that's actually just an "over" pipe. the actual downpipe is somewhere in the 1.75" range(I think even 1.5" at portions), then it hits the cat and comes out at 2" post-cat.

    different theories have been thrown around and I think it's a good mix of the 3 big ones: lower emissions, less heatshielding necessary and more quiet engine operation.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  10. #10
    Fuel Injected!
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    Same double-walled construction on the 94-95 3.4L camaro engine as well. 2.5" tubes off the manifolds, but 1.75" tubes inside. Would have been a pain to weld up, but they did it!

  11. #11
    Fuel Injected! Terminal_Crazy's Avatar
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    Yay! Passed this morning.
    Blanking the 2nd tailpipe made a huge difference

    Took it back
    CO was virtually 0
    HC sat about 250-300
    Lambda was about 1.067

    Tester stuck a rag over the open tail pipe and everything just dropped to green
    CO. 0
    HC. 130
    Lambda 0.997

    So that tune is a keeper!

    I actually think it would have passed last week if we'd blanked the tail pipes off.

    Awesome guys.Thankyou all very much.
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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    Congratulations!

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