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Thread: Emissions fail - high hydrocarbons in exhaust

  1. #11
    Stupid Newbie DaraSue's Avatar
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    Technically I could register it as "vintage" and not have to smog it but officially you're not supposed to daily-drive it. I'd rather have it running correctly because I still want to drive it a lot and after all the cash I've dropped on it, I feel like it should be perfect. (Also I'd have to give up my vanity plates if I did that and get one with only 5 letters.)

  2. #12
    Senior Member NckT's Avatar
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    Quote Originally Posted by NckT View Post
    Disconnect the oxygen sensor electrical connection first and see if it buzzes. If it does when the engine is cold but stops when the engine is warm, then the duty cycle may have gone full swing such that the valve is fully open or fully closed.

    I'll assume you've not replaced the lambda relay lately, as this needs a double contact single throw type.

    Does the DPI "performance" exhaust have catalytic converters in?

    Have you done fuel pressures tests?
    Done any of the above yet?

    Disconnecting the electrical connection from the oxygen sensor defaults the fuel computer to operating the frequency (bleed off) valve to 50% duty cycle ie it buzzes. This is when the car is at operating temperature.
    The reason I asked if it buzzes when cold is that the lambda switch should default the duty cycle to 60% and you should hear it buzz.
    If it buzzes when cold but not when hot then as described above it goes full swing one way.

    If you don't hear it buzz at all with the oxygen sensor disconnected then it'll be an electrical issue. This is usually brought on by someone replacing the relaid in the relay compartment without taking note that the lambda relay is a particular type described in the previous post hence the question.
    In a small number of cases with a good oxygen sensor confirmed looking at the trace with an oscilloscope and frequency valve not buzzing due to swing of the duty cycle and fuel mixture is correct with oxygen sensor disconnected, then the quad op amp in the fuel ecu has gone bad and needs replacing.
    Last edited by NckT; 08-27-2018 at 06:04 AM.
    RIP Rob van de Veer Top bloke

    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  3. #13
    Stupid Newbie DaraSue's Avatar
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    I didn't have time to do much with it today except verify that the FV was buzzing. I'll go over there tomorrow and try disconnecting the sensor to see what happens.

    The seller replaced the relay box before I got it and I think everything was legit but I'll double-check that it's the right one.

    Haven't done a fuel pressure check yet that I know of. I'll see if they can try that tomorrow. Would I notice other symptoms if that were the issue? Seems to be running pretty normally.

  4. #14
    Senior Member Rich's Avatar
    Join Date:  May 2011

    Location:  San Francisco Bay Area, Calif.

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    Some answers to earlier questions are inserted below. And an easy check before you go to the trouble of checking the fuel system.

    Assuming the business end of the O2 sensor is OK you might also be sure that the black wire to the sensor isn't grounding out anywhere, that no varmints have chewed it apart and that the other end of it is well-connected to the Lambda computer.

    Quote Originally Posted by DaraSue View Post
    The car's at the shop so I'll have to go by and check out the frequency valve on Mon.

    The exhaust IIRC is dual-cat, but was installed by the guy who sold me the car, not actually done at DPI. He said he put a new O2 sensor in, not sure if it came with the exhaust kit or was purchased elsewhere. Are these sensors specific to the car or can they be bought off the shelf? They are not D-specific - they were used on lots of cars of our vintage and are still widely available.

    I did have an issue where the O2 sensor was coming loose last year. Could something have gotten into it or gotten damaged? Unlikely that the sensor is bad at the business end since it smogged OK after your fix and it had no sealer on it and it's so new. Although the last time it happened (that I noticed) was around May and it had passed smog since then. It didn't have any sealer on that I noticed.

    I generally only buy name-brand, top-tier certified gas, so it shouldn't have had any lead in it, should it? Aviation gas still has lead in it, I think. No gas stations sell leaded that I know of.
    March '81, 5-speed, black interior

  5. #15
    Stupid Newbie DaraSue's Avatar
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    Is the o2 sensor supposed to just unplug somewhere? Mine looks like it's been soldered & heatshrunk on the sensor end.

    Also does this look right?

    20180828_121940.jpg
    Last edited by DaraSue; 08-28-2018 at 02:22 PM.

  6. #16
    Stupid Newbie DaraSue's Avatar
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    Just noticed the top two bolts are off the airbox. I thought they took them off here but the mechanic says they didn't. The bix is pretty loose, would that be enough to screw up the test results?

  7. #17
    Delorean Guru
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    No. Make sure there is a plug in the hole over the mixture screw though.
    David Teitelbaum

  8. #18
    EFI'd dn010's Avatar
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    Location:  Florida: Pinellas County

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    Quote Originally Posted by DaraSue View Post
    Is the o2 sensor supposed to just unplug somewhere? Mine looks like it's been soldered & heatshrunk on the sensor end.

    Also does this look right?

    20180828_121940.jpg
    Follow the 02 wire from the sensor back. The wire is long. It should have a large rubber connector down the line that connects it to the larger blue wire. The connector should be going into the car through the fiberglass behind/above the rear driver side tire, on the outside of where all the blue wires are that you have pictured.

    I don't see anything alarming in the photo other than the rubber grommet pushed back from the fiberglass, push it back and into the fiberglass to seal up the hole that is there without it.
    Last edited by dn010; 08-28-2018 at 03:48 PM.
    -----Dan B.

  9. #19
    Stupid Newbie DaraSue's Avatar
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    I couldn't even find the other end of it but one of the mechanics said that where it went into the bulkhead there was a lot of leftover wire knotted up, is that normal?

  10. #20
    EFI'd dn010's Avatar
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    The 02 sensor wire is pretty long, I wouldn't be surprised if someone tied the excess up. Here is a photo of the wire, courtesy of DAP. It is the only photo I could find quickly for you. When installed correctly, the blue wire is pushed all the way into and sealed into the fiberglass with the rubber piece you see extending.

    https://www.deloreanautoparts.com/de...connection.jpg
    Last edited by dn010; 08-28-2018 at 03:55 PM.
    -----Dan B.

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