Emissions Test Failure! Please help!
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5.0 and 5.7 Discussion, Emissions Test Failure! Please help! in Cadillac Engine Technical Discussion; 1986 FWB 307 5.0. Just went to have the annual emissions test & failed with the following readings: HC ppm ...
  1. #1
    wytdog is offline Cadillac Owners Member
    Automobile(s): 1986 FWB
    Join Date
    Oct 2004
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    Stone Mountain, GA
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    Emissions Test Failure! Please help!

    1986 FWB 307 5.0. Just went to have the annual emissions test & failed with the following readings: HC ppm 173 reading, allowed 130. CO% 4.51 reading, allowed 0.83. These readings were on the 25/25 test. Here are the readings on the 50/15 test: HC ppm 146 reading, allowed 134. CO % 4.36 reading, allowed 0.75. The tester said that he had no idea would could be causing these readings (I have no clue what the readings even refer to). I was wondering if anyone can educate me on what is going on with my beloved "Hawg", before I take it to a shop.
    Thanks.

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  3. #2
    Cadillac_Fan's Avatar
    Cadillac_Fan is offline Cadillac Owners Fanatic
    Automobile(s): '92 Brougham d'Elegance 305; '98 Seville STS
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    Re: Emissions Test Failure! Please help!

    I wish I could help you, but I am not knowledgeable about emissions. (Unfortunately, the overarching problem is the fact that state government dictates the cars we drive, toilets we install (low-flow), and the annual confiscatory "rent" we pay in personal property taxes for what we own.) Yet I digress.

    I feel for you, and hope someone in the forum has an idea how you may pass the emissions test. Having lived in Northern Virginia / suburban DC, I was constantly abused and taken by the garages which perform state inspections. Conveniently, without fail, they always found a $600 repair before passing my car and pasting the cumbersome sticker on the center of my windshield.

    (Forgive the rant, I just have empathy for your situation!)

  4. #3
    Rick186 is offline Cadillac Owners Fanatic
    Automobile(s): 1995 Fleetwood Brougham
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    Re: Emissions Test Failure! Please help!

    wytdog -
    I think your 307 is an Oldsmobile base motor. I think that our resident expert is N10DH.
    If he's lurking, he may be able to help you.
    Right now, from the readings, it looks like you may need one helluva tune up. Maybe even one good road trip.
    Then again, I know as much about the 307s as could fill a thimble and have enuf room for a locomotive.

  5. #4
    joe_padavano is offline Cadillac Owners Member
    Automobile(s): 93 Allante
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    Re: Emissions Test Failure! Please help!

    Your engine IS a 307 Olds with the computer controlled Quadrajet carb. I recently got mine past Virginia emissions and became very familiar with the 307 in the process. This carb uses a solenoid that's controlled by the computer. The solenoid raises and lowers tapered metering rods in the primary jets, which varies the air/fuel mixture ratio. The computer pulses the solenoid many times a second in response to the oxygen sensor and temp and pressure sensors on the engine. High readings of HC and CO mean your engine is running rich, which also means you're wasting gas (and money), so it pays to fix this.

    This particular engine uses a number of different emissions components, any one of which can cause a problem. The first thing to do is a complete tuneup. Plugs, cap, rotor, air filter, fuel filter. If the carb hasn't been rebuilt in a while, this should be done also. Replacing the oxygen sensor is also a good idea. Then be sure everything is adjusted exactly right. There's a fairly intricate procedure in the factory service manual and it must be followed exactly.

    At the same time, a complete check of all the systems on the engine should be done. This includes the feedback system for the carb, the choke and fast idle system, the heat riser valve on the exhaust manifold, and the air injection system. There's actually a very simple way to test the feedback solenoid. There's a green single wire connector in the harness directly in front of the carb. Connect a regular dwell meter to this terminal and set the meter to the six cylinder scale. With the engine running, you can read the solenoid duty cycle directly as dwell on the meter. Adjust the idle mixture screws to get approx. 30 degrees of "dwell" on the meter. You can also test to see if the sytem is working properly - once the oxygen sensor is warmed up, the "dwell" reading should be constantly varying (28.6, 29.2, 30.1, 29.7, etc.), which shows that the oxygen sensor is working and driving the mixture ratio. If the dwell reading is fixed or at the extremes (below 15 deg or above 50), there's a problem with the system. This carb is also sensitive to adjustment of the throttle position sensor, so once the engine is idling correctly, the TPS should be adjusted per the factory procedure. The 307 has miles and miles of vacuum hoses, any one of which can crack and cause a problem. Carefully inspect and (if necessary) replace the hoses. Finally, the 307 is also sensitive to petroleum vapors in the oil pan, apparently due to the PCV system. Be sure to change the oil just prior to having the car emissions tested. Yes, this sounds crazy, but it's proven to make a difference.

    Again, there are dozens of pages in the factory service manual devoted to this process, so I can't go into it in detail here. Either get an FSM or find a mechanic who knows what he's doing. Most "mechanics" today are just parts replacers and use a "shotgun" approach to repairs. Eventually, something they replace will fix the problem, but meanwhile the customer has paid for a bunch of parts that were unnecessary. Few take the time to properly test and diagnose problems.

    Once the 307 is properly tuned, it runs great. I got mine down to less than half of the required levels for HC, CO, and NOX. One other thing to watch for is that once you do fix whatever is causing the engine to run rich, you should drive the car for a week or so before testing. Carbon builds up in the exhaust system and will cause unrealistically high HC and CO readings. I had this problem with mine. I found and fixed several problems with the feedback system, but the car still failed the first time I took it in (the next day). The person running the test told me to drive it for a while to burn out the residual carbon. That did the trick.

    Good luck.

  6. #5
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
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    Re: Emissions Test Failure! Please help!

    Search on the HT4100 and Deville forum, RWD Fleetwood/Brougham and this one for CO, HC, and NOx, I have a lot of info in those posts.

    What Joe said too! What he said about mechanics these days one of my big beefs about shops you PAY them to work on your car. Most know little other than "I think this might do it" "nope, lets try this" etc

    Nutshell, CO is not enough O2 present for combustion, HC is the flame not exposed to all the fuel, and NOx is combustion chamber temps too high (lack of EGR and/or lean mixture, commonly occurs with high HC).

  7. #6
    ChiTDI is offline Cadillac Owners Member
    Automobile(s): '86 Brougham
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    Re: Emissions Test Failure! Please help!

    wytdog -
    The last two posts are filled with correct responses from knowledgeable people. Nodih's posts got me through the last emissions tests in August. Carb rebuild and cat replacement are the big dollar issues.
    Keep us posted.

  8. #7
    wytdog is offline Cadillac Owners Member
    Automobile(s): 1986 FWB
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    Stone Mountain, GA
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    Thread Starter

    Re: Emissions Test Failure! Please help!

    Parked "The Hawg" for a couple of months, finally got around to doing all the suggestions listed in the postings (major tune up: be sure to check the timing, replaced some worn vacuum hoses etc.) passed the test with no problems. Thanks to all who helped!.
    Wytdog

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