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Thread: 84 Grand Marquis with engine stutter while cruising

  1. #1

    Default 84 Grand Marquis with engine stutter while cruising

    I'm about to admit defeat on this one, hopefully you guys can help as well as you did with the transmission issue.

    The car is an 84 with the 5.0 and AOD, 133,000 miles, all original right down to the tail pipe. It's my friends car and had been having problems with stalling, severe bucking, and random no-start. When it wasn't having any of these antics, it ran very smooth and drove great (no stuttering). I replaced the plugs, wires, distributor cap and rotor, as well as the TFI module at the suggestion of a friend and seconded by someone here. It no longer stalls, bucks or has any issues starting, however... when cruising at speed, say 45 mph, it stutters. It's a bit random, and it sort of feels like a partial misfire. It doesn't do it when accelerating, and it doesn't do it at high speed, like 70-75 mph (or if it does I can't feel it). It does it at low speeds, and medium speeds. It does it with OD on and with it off.

    Here's the annoying part. I replaced the TFI module (with an oem Ford Motorcraft part) before I replaced the plugs and cap and rotor. On the night I replaced the TFI module I took it out for a drive afterwards to test the new TFI and it ran beautifully. No problems of any kind at any speed. It was probably around 70 degrees that night, possibly cooler (I mention that because that's cold for a Florida summer night and it hasn't been that cool since). I parked it in the driveway and let it sit overnight I started it up the next day to take it for a final drive before giving it back to my friend... and the stutter started.

    Replacing the distributor cap and rotor (old one had aluminum lugs, new one has brass) seemed to help, but only lessened the intensity of the stutter, it still basically acts the same way. Replacing the plugs (with plain Autolite 26, gapped to approx. 53) had no effect (though one of the old ones broke when removing it). I checked the timing with a light today and it was a smidge off the old paint mark, nothing that would affect performance. (A smidge is maybe a 1/4 inch on the crank indicator, the markings are too dirty to read the degrees.) I did also disconnect that one certain wire before checking the timing as per instructions. I ran the gas tank until almost empty and then filled it up and drove it almost 100 miles with the new gas. I disconnected the negative battery cable and let it sit overnight as suggested by a friend. Today I put the old TFI module back on and it still stutters. It also didn't exhibit any of the old starting/bucking/stalling issues for the 10 minutes I drove it around with the old TFI module. Going to put the new TFI module back on tomorrow and recheck the timing with that one.

    The only other things I did to the car were replace the old rusted out tail pipe with a new one, adjust the TV linkage on the transmission due to hard shifting as suggested in my other thread, clean a few electrical connections, and remove some transmission fluid after it'd been slightly over filled by a shop.

    I'm thoroughly stumped.

  2. #2
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    Have you replaced the fuel filter on it? Maybe drop an known good distributor into it? There was also a TSB from Ford on this you could try (courtesy of another site) that you could try before resorting to replacing the dist.

    The problem you have happening is caused alot of times by arcing of the spark plug wires.
    There was a service bulletin put out by Ford for this same problem with stumbling an bucking.
    The remedy was placement of the #4 and #8 spark plug wires.
    #4 needs to be isolated by going from the spark plug to around the rear of the valve cover and have the wire sit on the valve cover ledge on the intake manifold side.
    #8 wire on the driver side is routed the same way.
    These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.

  3. #3

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    Thanks! I'll give that a try tomorrow. That spark plug wire routing issue would make sense. The old wires were the same brand, but they were much longer. The new wires I got are shorter, "custom fit," and so I routed them differently than the old wires because of the difference in length.

  4. #4
    Member Arquemann's Avatar
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    I think I might have had the same type of issue. I replaced my TFI,(and everything else) and then replaced my TFI again and now stuff works.
    While I still had the problem, I reorganized my plug wires too and it did help slightly. Mostly the idle though.
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

  5. #5
    I'm an air-conditioned gypsy gadget73's Avatar
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    Is the timing mark holding steady? if its dancing around that indicates a sloppy timing chain and that will cause you trouble.

    If thats good, a distributor pickup is really the last thing on the common items list that I can think of.

    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

  6. #6

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    Rearranged the plug wires today according to the TSB, but modified it so that #4 and #8 are as far away from every other wire as they can be, laying along the top of the valve cover. Still stuttering. However, this time I didn't bother letting the engine warm up, or drive it around the block first like usual, I just went straight to the main road and it was smooth with no stutter for the first half mile or so, during which time I was potentially elated... until I turned onto a side street and it started to stutter again.

    Then I let the car sit for a couple hours, put the new TFI module back on, checked the timing, all good. Took it immediately on the exact same drive as before, and like before it was totally smooth for almost a half mile (at which point the road ends). Turned down a couple side streets and drove back the way I came... back to stuttering. Wtf.

    Could it be something temperature related? Since the first time I drove it with the new TFI it was cold out and it ran perfectly smooth, and today with the engine not yet warmed up it was smooth for a short while, twice.

    The timing mark holds perfectly steady.

    Also the fuel filter was replaced by a shop about six weeks ago.
    Last edited by DrVlikhell; 04-21-2020 at 08:02 PM.

  7. #7
    I'm an air-conditioned gypsy gadget73's Avatar
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    did you put thermal paste on the TFI module? It needs to have some on there or it will get too hot.

    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

  8. #8
    Road Warrior Kodachrome Wolf's Avatar
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    Coolant temperature sensor could be suspect if it's not within adequate range. That sensor should be the one coming off the intake on a heater pipe. It communicates to the ECU to help adjust fuel based on engine temperature.

    My Cars:
    -1987 Grand Marquis Colony Park LS (325K Miles) - April 2017 + September 2019 POTM Winner
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  9. #9

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    I used the same thermal paste I use for putting computer heat sinks on cpus. Protronix brand, supposedly rated at 3.17W/(m-K) for thermal conductivity.

    Would that temperature sensor be in the rear, just behind the throttle body?

  10. #10

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    I think I'm raising the white flag. Had a look at the temp sensor, found it on the front of the intake manifold, definitely been replaced recently cause it's clean and shiny. Went to go take it for a drive to see if I could duplicate how it drives smooth briefly after a cold start, and it did drive smooth, then started stuttering as expected. So I shut it off in the middle of the road, started it back up and damn, it drove smooth again. Then it started stuttering... then it started stalling... then it started bucking hard and it barely made it back to the house, stalled as it rolled into the driveway.

    When it was bucking and wanting to stall, in my sudden fear of possibly having to push a 2 ton car home while wearing sandals, I stomped on the throttle and it came to life, stopped bucking, roared down the street... until I had to take my foot off the throttle to slow down for a turn, then back to harsh bucking. I don't get it, I drove it around 100 miles after I replaced the TFI and it was fine except for the stutter.

    The only thing I can think to do is return the TFI for a replacement, and then give the car back to my friend with an apology.

  11. #11
    Road Warrior Kodachrome Wolf's Avatar
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    I remember my when my TFI module failed, it ran like crap and broke up real bad unless floored. I'd rather not say you've got a bum TFI since that would be lame, but the "runs good when cold, then when it starts warming up it gets odd" sounds kinda in line with that.

    My Cars:
    -1987 Grand Marquis Colony Park LS (325K Miles) - April 2017 + September 2019 POTM Winner
    -1989 Sable LS Wagon (88,710 Miles) - Sold
    -1997 Grand Marquis LS (210K Miles) - The Daily Workhorse & March 2015 + January 2019 POTM Winner

  12. #12

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    Yeah it sounds like a bum TFI to me too, except that the day before yesterday, it ran fine except for the stutter. I drove it quite a lot, went to several places with it and even let it sit idling for a while which had it pretty hot. The whole day it never had any issues except the stutter. Normally I'd figure that the new TFI module was faulty out of the box and is the cause of the stutter and finally pooped out last night, except that the car still stutters with the old TFI module back in it. And it never stuttered before when it the car was first brought to me and had the old TFI in it.

  13. #13
    I'm an air-conditioned gypsy gadget73's Avatar
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    Its the 2 wire temp sensor in the heater hose fitting, not the single wire sensor directly in the manifold. The single wire one is the overheat light, the other one is what the computer uses.



    bad pickup in the distributor can act like a bad TFI. You've already done the TFI twice with no result, I'm inclined to say that isn't the problem.

    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

  14. #14

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    I've read a few other things that say the same thing about a bad pickup acting like a bad TFI. Do you know if the pickup on an 84 can be replaced by removing the plate on top of the distributor, or is it the pain in the butt one where you have to remove the gear at the bottom and then slide the shaft out through the top?

  15. #15
    I'm an air-conditioned gypsy gadget73's Avatar
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    Gear comes off and the shaft comes out through the top.

    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

  16. #16

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    Looks like that requires a press and other things I don't have in order to get the gear off. Alternative option seems to be replace the whole distributor. There are options with a steel gear or iron gear, any idea which gear this car has?

  17. #17
    Wagon Addicted Tiggie's Avatar
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    84 would be the iron gear.
    1988 Crown Vic Wagon - daily
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    Other: 95 Ranger, 74 F250, 68 Mustang, 94 Mustang
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  18. #18
    I'm an air-conditioned gypsy gadget73's Avatar
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    yes, iron gear.

    replacement distributor is the easier fix. I'm lucky enough to have a press at work. I have seen it done using a piece of pipe and a hammer but that makes me cringe.

    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

  19. #19

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    I replaced the distributor with a Cardone remanufactured one from RockAuto. Nice to see that it's a Ford Motorcraft part that was rebuilt and not some cheap copy. Ended up replacing the cap and rotor again because the new distributor uses a different rotor, and also replaced the distributor cap adapter because the old one had the wrong screws in it. I warrantied the new TFI module cause it was definitely dead and got another new one. Assembled and installed the distributor, which now consists of entirely new and never used parts... And the car still stutters, exactly the same as before. Even seemed like it wanted to stall once coming up to a stop sign. I'm out of ideas.

  20. #20

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    I didn't do a thing to it since parking it last night and this morning it's even worse. It will barely stay running and wants to stall just trying to idle in the driveway. I think it's possessed... and mad at me.

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