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Thread: mixture setting/rich smell?

  1. #11
    '82 T3 Turbo FABombjoy's Avatar
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    Quote Originally Posted by David T View Post
    FHe needs to figure out why it doesn't get into closed loop. It could be fuel pressure, it could be a lot of things.
    There are only a couple of reasons to be in open loop mode:
    1: Bad/disconnected O2 sensor
    2: Cold engine
    3: WOT switch engaged.

    2 & 3 both relate to the same wire being grounded

    If you're crazy rich the dwell meter will fall to nearly nothing as the system attempts to lean out the mixture
    If you're crazy lean the dwell meter will spike high

    AFR on a warm engine stuck in enrichment mode will dip as low as 10:1

    If the dwell is fixed in the middle and doesn't vary the system is electrically stuck in open loop. I wouldn't chase down a fuel pressure solution until the electrical component has been ruled out.

    Disconnect the WOT switch and see if the dwell starts to vary (WOT switch stuck). If not, see if the light green wire on the connector has continuity to ground (thermistor stuck grounded).
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X In Process :: DevilsOwn Methanol Injection

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  2. #12
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    Read the original post, he states it's dwell is steady between 42 and 45 which is bang on where it should be.

    If it's swinging like this then it's fine. Mine was a tad high here as it was going up to 47, but it's in the ballpark, and doesn't smell of fuel either...
    https://youtu.be/DB5pSdGc2fM

    Fuel pressure test is the way to go, if I was a betting man my money is on out of spec CPR.
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  3. #13
    '82 T3 Turbo FABombjoy's Avatar
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    Quote Originally Posted by MikeWard View Post
    Read the original post, he states it's dwell is steady between 42 and 45 which is bang on where it should be.
    If the exhaust is eye-watering rich it should be attempting to lean the mixture and would not be anywhere near 45.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X In Process :: DevilsOwn Methanol Injection

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  4. #14
    Member NckT's Avatar
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    Quote Originally Posted by FABombjoy View Post
    If the exhaust is eye-watering rich it should be attempting to lean the mixture and would not be anywhere near 45.
    Not when the engine is cold due to the lambda switch or if the oxygen sensor is not hot enough to give signal feedback
    RIP Rob van de Veer Top bloke

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  5. #15
    Member NckT's Avatar
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    http://dmctalk.org/showthread.php?15...064#post224064

    Rjd2, is your cold start fuel pressure still as per your video on the above post on another thread?

    If it is, the control pressure should not additionally drop when you rev it. The vac delay valve should keep the control pressure lower for between 8 to 12 seconds.
    Disconnect the vacuum pipes to the cpr and block the river/ silicon pipes that have been removed. Also disconnect the grey electrical plug off the CPR

    You'll have to include more information on the cold start (engine left overnight), such as the temperature of the control pressure regulator (CPR / WUR).
    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....

  6. #16
    '82 T3 Turbo FABombjoy's Avatar
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    Not when the engine is cold due to the lambda switch or if the oxygen sensor is not hot enough to give signal feedback
    O2 should be active within the 5 minute window given by the OP. Lambda switch should be off well before 2 minutes.

    Some reference data:

    Cold start (25f morning, -4c)
    Orange trace is duty cycle (dwell-type spec * 10%)

    Difference here is that I'm running a WBO2 controller which will have an active signal before the stock 1 wire, hence the immediate reaction shown in chart #2

    Thermistor transition out of cold start visible. Jetronic computer immediately attempts to lean a very rich mixture. DC goes from 63% to 15%
    cold_start.jpg

    CPR transitioning toward warm pressure range. Mixture leans and frequency valve is now within operating range. DC starts to swing.
    warming_up.jpg

    Warmed up, DC fluctuation is now minimal. Total time under 5 minutes. RPM is high as I was adjusting the throttles / idle switch.
    even_warmer.jpg
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X In Process :: DevilsOwn Methanol Injection

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  7. #17
    Member NckT's Avatar
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    Thank you for your data. This does not equate to the fact that the cold start is very rich to the point of saturating hydrocarbons on clothes. .. within that 5 minute window as you say.

    I've lost count the number of CPR's I've overhauled and re calibrated because of this issue, as well as fuel diagnostics.

    I'll let you help the rjd2 out, no problem.
    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....

  8. #18
    '82 T3 Turbo FABombjoy's Avatar
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    Quote Originally Posted by NckT View Post
    I'll let you help the rjd2 out, no problem.
    That is the goal, right? To be helpful?

    All I am suggesting is to test for an electrical short before proceeding to fuel system tests.

    rjd2's issue mimics my own experience with a stuck WOT switch, as has also been experienced by others on 'talk. First post indicates he was just working with the thermistor circuit which is directly involved.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X In Process :: DevilsOwn Methanol Injection

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  9. #19
    Senior Member Bitsyncmaster's Avatar
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    I also run a wideband unit so I go closed loop in about 15 seconds after engine start (wideband is a heated sensor).

    But even with that quick controlled mixture, sometimes if the wind is just right blowing into the garage I do have that rich mixture smell right after starting. I remember running a tail pipe wideband test and the mixture does start out in the 10 AFR range (i think).
    Dave M vin 03572
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  10. #20
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    Ok, a bit more data:

    -I have a BRAND new CPR unit in place as of January 2017. I'm not sure how to test it, but for the first half of the year, it showed no problems.
    -I can tune the dwell to hang right around 40, and it won't oscillate at all. When I tuned it any leaner, what I got is the idle jumping up to 1500-1700; it would skip any "warm up" period and go straight to HIGH. I tuned it back rich, to where the idle seemed solid, and left it.

    For now, I've got the car able to hang right at ~750ish RPM at idle, and a dwell around 40. I haven't put it through any longer test periods than 5-10 minutes; I'll get some regular usage in, some longer run periods, and see how it goes. (as an aside, at this point I believe the O2 sensor is the only thing in the fuel system that HASN'T been replaced.) Thanks for the help everybody!

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