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Thread: My '85 MGM, "Maisa"

  1. #721
    Lost and driftin' Arquemann's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    chuff.. chuff.. chuff" noise from the exhaust
    Sounds kinda familiar, but it could also be a misfire.
    I did a compression test, cyls 1-7 are all right around 145-155 psi (10-10,5 bar) and I can't get the compression tester to cyl 8. The no. 8 plug wasn't fouled atleast, quite the opposite...





    I ran out of time today, I'll get her back together tomorrow. Tomorrow might bring more surprises.
    I don't know what the actual fuck is going on anymore...
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    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

  2. #722
    GMN Regular DerekTheGreat's Avatar
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    Those numbers sound good to me. The plugs look good too, how many kms/miles are on 'em? The ground electrode on #1 & #7 (possibly # 4 too, possibly just the lighting) look a little wet compared to the others, but none are the smoking gun I was hoping to see. With the engine that came out of my truck, #1 was CAKED with carbon/oil all in the spark plug gap.
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  3. #723
    Lost and driftin' Arquemann's Avatar
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    Here's the problem with those plugs:
    The shop receipt from a couple years back says 8pcs of NGK UR45. Which those are NOT, those are some rusty old ACDelcos. I have no clue how old those are or how many miles are on them.
    It seems I was bullshitted on those plugs, or the mechanic put the old ones back in if the NGKs made no difference.
    To me most of those plugs look way too white, which would indicate those getting hot.

    I THOUGH I HAD NEW-ISH PLUGS.

    Yesterday I put in completely new Champion coppers and new 8mm plug wires, and today I took her for a rip. The bucking on decel is pretty much GONE. Idle sounds smoother, while it doesn't really feel that different.
    -There's still some... ehm "inconsistency" slowing down from about 25 to 15 mph.
    -Also some bucking on very light throttle at about 45 mph.
    -Driving at very low throttle the mixture goes lean, to about 16 AFR at worst, doesn't affect anything much. Mixture is instantly fine if more or less throttle is applied. Is 16 AFR harmful at such low load situation?
    Just a thought, but my transfer slots might be too closed, which might cause this.

    At this point, I need to drive it more to know how things stabilize and to see how things act consistently.
    PLUGS, PLUGS FOR FUCK'S SAKE!
    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

  4. #724
    Still Wrenchin'! friskyfrankie's Avatar
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    Did I not mention a misfire? Good job on NOT assuming anything and checking thew plugs and wires!!
    What I Own: 1993 Mercury Grand Marquis GS
    What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

  5. #725
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    Quote Originally Posted by friskyfrankie View Post
    Did I not mention a misfire? Good job on NOT assuming anything and checking thew plugs and wires!!
    Yeah I was thinking it was a misfire aswell, but it took me long enough to question the shop receipt that says I have new plugs. I have no idea how much money and time I've wasted due to a bullshitting mechanic.
    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

  6. #726
    Still Wrenchin'! friskyfrankie's Avatar
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    Quote Originally Posted by Arquemann View Post
    Yeah I was thinking it was a misfire aswell, but it took me long enough to question the shop receipt that says I have new plugs. I have no idea how much money and time I've wasted due to a bullshitting mechanic.
    Unfortunately, it is the folks we trust that disappoint us. You did ALL the right things, checked even things you thought were fine and narrowed down the problem (or at least part of it). I congratulate your persistence and hope you have many years of enjoyable driving on this car. Having an older car is a challenge - something always requires repair but that is part of the "charm" of older car ownership.
    What I Own: 1993 Mercury Grand Marquis GS
    What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

  7. #727
    Wagon Addicted Tiggie's Avatar
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    My experience with the AOD leads it to be a bit clunky on decel around 15-20mph as it pulls out of locked third and into second. Especially true if the TV pressure is up a bit.

    I think 16:1 is okay if it is low load. It doesn't take much throttle to load up a lugging 302 hanging out in 3rd at 20-25ish mph. If it pings, it might be something to worry about.
    1990 Country Squire - weekend cruiser, next project
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  8. #728
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    Quote Originally Posted by Tiggie View Post
    My experience with the AOD leads it to be a bit clunky on decel around 15-20mph as it pulls out of locked third and into second. Especially true if the TV pressure is up a bit.

    I think 16:1 is okay if it is low load. It doesn't take much throttle to load up a lugging 302 hanging out in 3rd at 20-25ish mph. If it pings, it might be something to worry about.
    Yeah the downshift could be the cause for that issue. My TV pressure is up from factory aswell. That issue was the least of my worries anyways.

    I'll fiddle around to figure out the tendency to lean out. Initially I set the transfer slots to squares, but I've had to slow down the idle speed quite a bit from that. Currently the idle speed fine, but I wonder if the transfer slots aren't exposed enough so it leans out at low throttle before the accelerator pump hits. I'll check for vacuum leaks aswell, I know for sure the automatic e-brake release leaks 9/10 times.
    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

  9. #729
    GMN Regular DerekTheGreat's Avatar
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    Quote Originally Posted by Arquemann View Post
    Here's the problem with those plugs:
    The shop receipt from a couple years back says 8pcs of NGK UR45. Which those are NOT, those are some rusty old ACDelcos. I have no clue how old those are or how many miles are on them.
    It seems I was bullshitted on those plugs, or the mechanic put the old ones back in if the NGKs made no difference.
    To me most of those plugs look way too white, which would indicate those getting hot.

    I THOUGH I HAD NEW-ISH PLUGS.

    Yesterday I put in completely new Champion coppers and new 8mm plug wires, and today I took her for a rip. The bucking on decel is pretty much GONE. Idle sounds smoother, while it doesn't really feel that different.
    -There's still some... ehm "inconsistency" slowing down from about 25 to 15 mph.
    -Also some bucking on very light throttle at about 45 mph.
    -Driving at very low throttle the mixture goes lean, to about 16 AFR at worst, doesn't affect anything much. Mixture is instantly fine if more or less throttle is applied. Is 16 AFR harmful at such low load situation?
    Just a thought, but my transfer slots might be too closed, which might cause this.

    At this point, I need to drive it more to know how things stabilize and to see how things act consistently.
    PLUGS, PLUGS FOR FUCK'S SAKE!
    White also means a lean mixture, which is what I'd be leaning towards and what I'd prefer.

    Perhaps there is some bit of crossfire going on, if changing the plugs and wires made a big difference with your issue. At night, try spritzing some water around all the plugs, coil, dizzy cap and along the wires as it runs. If anything changes, investigate further.

    16:1 at cruise is great, I wouldn't change it. It's only lean on acceleration/load one needs to worry about, as that's what'll cause combustion temps to increase and all that. General Motors TBI stuff has a lean cruise feature built in. I'm not sure what regions had it enabled, but it's mostly disabled. Reenabling it is something a lot of folks do to increase their cruise mpg, it's worth about 10-20% depending on the application. I want to say 16 or 16.5:1 was what the ratio GM targeted was. Downside (if you care) is increased NOx emissions. Should also be noted there is a better pay off with EFI, as I believe it also runs the EGR for combustion chamber fill and advances the timing to compensate for the lean mixture.
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  10. #730

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    Nice job getting to the root of it. I’m surprised plugs would cause a misfire on decel due to the extremely low load the engine is under. I would have thought the miss would have been more noticeable under hard acceleration.


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  11. #731
    Lost and driftin' Arquemann's Avatar
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    Regarding the leaning out, going as far as 16 AFR but only at very light throttle, not really representative of cruising speed. I adjusted the accelerator pump arm since it had a bit of play in it. It might fix it, might not. Not too worried at this point, since it's seemingly not affecting anything.
    I'll have play around with this thing, get to know the behaviour first, then I'll continue tuning it.

    Shot around some bräkleen aswell, no obvious vacuum leaks to be found. Also I did plug the e-brake release, so it won't leak in any position. With the brake release plugged and the AC in off position, there's genuinely zero vacuum leaks from the vacuum distribution block!

    I'll drive it around more tomorrow, try to figure out if the 45mph bucking is gone or what's it doing then.
    But dang, on cold start this thing sounds good! The cold start and idle sound changed quite dramatically with all 8 cylinders firing well lol.
    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

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