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Thread: 1984 Grand Marquis EFI problem

  1. #1
    n00b
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    Default 1984 Grand Marquis EFI problem

    Hello everyone!

    This is my first post here because I'm at the end of my rope. Six years ago I bought a 1984 Mercury Grand Marquis LS on the cheap. Considering its high mileage of 310,000 (now 327,000) and a long list of previous owners on both sides of the Atlantic (I live in Germany), it was in pretty good shape, particularly the body. There was little surface rust and no missing parts.

    There was only one problem that's been pestering me ever since: The electronic fuel injection system. The engine never ran like it should, especially at idle. It would stall whenever the car came to a complete stop and respond sluggishly to gas pedal input.

    Now, six years and many, many attempts at fixing the problem later, the issue still has not been resolved. I've done pretty much everything conceivable, replaced every sensor, the fuel pump, and even the CPU, but to no avail. The basic problem remains.

    The engine will always start willingly and run okay while warming up, but then idle speed drops and the engine will go out at the stoplight. It accelerates and upshifts hestitatingly just like when I got the car.

    For the last few weeks, there was a glimmer of hope because the computer (I presume) upped the idle speed just a little and the engine would respond much better to the gas pedal and would not stall. Today, however, things were back to "normal".

    I've thrown everything but the kitchen sink at the injection system over the last six years, yet it continues to defy me. The only thing I haven't done so far is to replace the complete wiring harness because I have to find an OEM harness at a reasonable price and in good condition first.

    If that isn't feasible, maybe a more radical approach is in order, like throwing out all that electronic junk and replacing the fuel injection system with a good old-fashioned carburetor.

    What do you guys think? Your ideas would be most welcome. I really like my Mercury and would simply love to finally get it running properly so I can tackle other issues like new weatherstripping for the doors or a new vinyl roof.

    Thanks in advance for your input.

    Regards,

    Mercjerry

  2. #2
    Lost and driftin' Arquemann's Avatar
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    Welcome to the forums! Me, like many others, came here to find answers.

    Does it just run like garbage, multiple misfires? Have you verified that you get good spark on all cyls? How about timing?
    Just a couple quick suggestions from my own experiences, you might've done these already.
    - Try unplugging the SPOUT connector from the distributor and running the engine (image attached), that stops the ECM from adjusting the timing automatically.
    - Stalling when coming to a stop might indicate throttle position sensor, but you most likely have changed that. There are ways to check if it's good, someone more experienced can explain how.
    - Is your MAP sensor good? It can be verified pretty easily too.
    - Are your grounds good?

    I was almost ready to go carb with my MGM too, I even had it at a specialized shop for two months, spent almost 2k for pretty much nothing.
    Hopefully we can help get your problems sorted.
    There are a few craz- ahem, CFI enthusiasts here who'll hold on to it for dear life. Nobody here would say to ditch it unless everything is done and tried. Whatever your choices are, you'll get help here.
    Attached Thumbnails Attached Thumbnails tfi-module-schematic--gray-distributor-mount.jpg  
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

  3. #3
    Member atlantic3000's Avatar
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    try removing and cleaning your egr valve. it is probably stuck open with carbon. also check for blocked up catalytic converters . if they are blocked bust out the centers.

  4. #4
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    Arquemann,

    Many thanks for your unexpectedly speedy reply. I have changed both the Throttle Position and the MAP sensor, indeed, but I'll try the SPOUT connector next and check the grounds, too. It's a worthwhile first step.

    I'll keep the community posted on my success - or lack of it.

  5. #5
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    atlantic3000,

    You, too, deserve a sincere word of thanks for a lightning-quick reply and some interesting suggestions. I'll try them out and let you know.

  6. #6
    GMN Regular DerekTheGreat's Avatar
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    With that many miles, it's time to check slop in the timing chain, timing in general and compression. Verify those things first and then we can go from there.
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  7. #7
    Member of the Orb Alliance packman's Avatar
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    Gaskets may need changing. I know the intake gasket was going on my '86 Crown Vic in its final days. Also, check your Idle Air Control valve (IAC); it hangs off the side of your throttle body. The 1st pic on the bottom is the stock intake with the empty slot on the side of the throttle body where it sits; 2nd pic is an aftermarket intake with the IAC installed (just a reference to what it looks like). Unplug and unbolt it (take care of the gasket, you'll need it); and take some carb cleaner and spray it inside of the valve; it may be gummed up. I had the same problems with my '86 when we first got it and that did the trick. Then later I had the aforementioned intake gasket problem.

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    Last edited by packman; 09-17-2020 at 04:12 PM.

  8. #8
    Lost and driftin' Arquemann's Avatar
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    Quote Originally Posted by packman View Post
    Gaskets may need changing. I know the intake gasket was going on my '86 Crown Vic in its final days. Also, check your Idle Air Control valve (IAC); it hangs off the side of your throttle body. The 1st pic on the bottom is the stock intake with the empty slot on the side of the throttle body where it sits; 2nd pic is an aftermarket intake with the IAC installed (just a reference to what it looks like). Unplug and unbolt it (take care of the gasket, you'll need it); and take some carb cleaner and spray it inside of the valve; it may be gummed up. I had the same problems with my '86 when we first got it and that did the trick. Then later I had the aforementioned intake gasket problem.

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    That says '84 so I'd say it's CFI, so no IAC.

    And what Derek said, verify that it has steady and correct timing.
    If it's 327 000 KM, things are well worn, if it's in miles, you might be needing a full rebuild...
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

  9. #9
    I'm an air-conditioned gypsy gadget73's Avatar
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    If the EGR and all that check out, you may need to just adjust the idle to keep it running. There are two adjustments, the high idle and the base idle. Sounds like the high idle is OK and it drops out like it should. The base idle is set by adjusting the "sled" that the plunger thing in front of the throttle lever sits on. That will move the whole sled and open the throttle up a bit.

    If you have the iron intake with the removable EGR spacer under the throttle body assembly, you can remove that whole thing and clean out the carbon. If its got a nugget of garbage in there that keeps the valve open it will not behave. Aluminum intakes don't have this, you just have to remove the valve and clean out what you can get to.

    Id be surprised if the chain is original at over 300k but stranger things have happened. Quick and dirty check, remove the distributor cap and put a breaker bar on the crank. Rock the crank back and forth to gauge how much rotation before the distributor moves. If there is any significant crank rotation without the rotor following, the chain is sloppy. Also worth a compression test if you don't know the engine has been rebuilt or replaced at some point. Thats a lot of miles. If the motor is just worn out no amount of electronic diagnosis is going to fix that.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  10. #10
    n00b
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    My apologies: I forgot to mention that even though the car has 327,000 miles (526,300 kilometers) on the odometer, the engine does not. Due to some slack in the crankshaft bearings, I had it replaced with a remanufactured long block from the US (Exact Powertrain) three years ago. That was so much easier and cheaper than to have it rebuilt here in Germany. My highly capable local mechanic, a very thorough and conscientious fellow, checked the new engine and found it impressively well-built. So, to make a long story short, since the powerplant and therefore the timing chain has only just 10,000 miles on it, I'm pretty certain the timing chain is fine. Nevertheless, thanks a lot for your input.

  11. #11
    I'm an air-conditioned gypsy gadget73's Avatar
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    ok that should rule out a whole lot of possibilities then.

    Do you know if the replacement engine had the flat tappet cam or a roller cam? Reason I ask is the distributor gear for each is different, and a steel roller cam against the original iron distributor gear will destroy the gear. If the gear is worn it will have slop in the distributor similar to a bad timing chain and that will mess with the ignition performance. If the timing was not set properly it won't act right either.

    These things also respond very poorly to vacuum leaks, so be sure all of the lines are in good condition.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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