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1991 Mercury GM weirdness

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    1991 Mercury GM weirdness

    I have a 1991 Grand Marquis with the 5.0. Totally stock with 80,000 mile on her. The car was running great but the tranny was giving me fits this summer. Had a shop look at it and they recommended a rebuilt tranny as the original one was slipping and, in general, just tired. I bought the car from the stereo-typical little old lady down in California who probably drive the car everywhere in OD. Anyway...
    Had AAMCO rebuild the tranny in August and drove it for about two weeks and it started to slip again. Back to the shop and they replaced the torque converter, some sort of transmission pump, and cracked the trans open to look inside. So here is where is gets weirder. They had the car for about a month because they could not figure out why it was still slipping a bit. They couldn't figure it out and told me that it was probably the engine. They kept on and on about the intake manifold but they never tested their theory. They just gave me the car back and said, "Let's us know because we are stumped!"
    Here is what the car is doing. At idle with the car in D, it will move forward but has a hesitation to it, like a very minor bucking. Like the motor is missing or the trans is slipping slightly. I don't think the engine is misfiring, hard to tell other than the symptom I described. Give the car just a bit of throttle and the problem goes away. At speed, if the car is just above idle, it will do the same thing. A slight bucking. Give just a bit of gas and the problem goes away. At highway speed, you generally need more than just above idle and there is no problem. Around 30-35 though, it is pretty pronounced. I haven't felt the trans slip since the second rebuild. I don't think it is the trans. AAMCO says they checked everything even the TV cable.
    I have done a smoke test and replaced the EGR valve. I don't see any obvious vacuum leaks but I could be missing something as it is like a snakes wedding in the engine compartment. No trouble codes show up on the engine analyzer. It gives me 13 I think. Which is all good. I think it is 13. Whatever. It is the code for all good.
    Any thoughts? Other than never having AAMCO do the tranny...
    Thanks!
    Marcus

    #2
    Plugged Cat?

    *edit, or restricted.
    Last edited by Birdofprey; 12-19-2017, 04:05 PM.

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      #3
      A slipping transmission is when you put the hammer down and nothing really happens but the engine revving up. Doesn't seem to be the case with yours.

      Sounds like you have a slight misfire at near-idle engine conditions. 30-35mph is near idle as far as engine is concerned if the transmission is allowed to go into OD so early (from the factory they can do it, AAMCO should have reset the TV cable to prevent this but who knows if they really did). Keep the transmission in "D" (3rd gear) manually with the shifter, see if she still acts up at 30-35mph.

      Some vacuum lines run under the intake still even on the '91 models, they get cooked pretty well in there.
      The ones who accomplish true greatness, are the foolish who keep pressing onward.
      The ones who accomplish nothing, are the wise who know when to quit.

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        #4
        When was the last time it got a tune-up?

        try unhooking the egr valve vac line and see if that does anything. If it does you may have a sticky regulator that is opening the valve when it should not be. If no change, that wasn't your problem. Bum TPS could also be it if there is a dead spot just off idle.

        11 is all clear. Is that the engine running test or the stored codes? There are 3 sets of codes on a Ford. Key on, engine off, constant memory (stored codes) which spit out after the engine off test, and the key on, engine running test which is a functional self test. Do you get 11's for all 3?
        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 grandpa spec white and cranberry

        1984 Lincoln Continental TurboDiesel - rolls coal

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

        Comment


          #5
          On my 90 GM I had a speedometer shop put in a 140 speedometer. It ran great when I dropped it off and like shit with a bad misfire when I picked it up. It turned out the pickup coil went bad.
          90 Colony Park LS with GT 40 heads and intake. HO cam, 65 MM TB, 67 MM EGR spacer. Has a 75 MM Pro Flow mass air sensor. Borla XS mufflers. 3L55. Shift kit, 2000 stall Tq convertor...Bilstein shocks, front and rear sway bars.
          90 Colony Park LS 64,000 miles all original. 3L55 tow package....front and rear sway bars.
          91 Grand Marquis GS....HO motor..Bilstein shocks poly bushings and police swaybars. This one handles the best.
          70 Torino Squire with M code 351 Cleveland 3.00 has Magnaflow mufflers. Hidden headlights and power windows. All original

          Comment


            #6
            My 81 does this same thing kinda and I know it is my engine as it never did, before I swapped the original engine out. At low RPM there's a very obvious shudder/hesitation that goes away when you give it more gas. It's the worst when in 3rd gear and I'm going under 50km/h and when I'm slowing down and the trans downshifts into 2nd

            Comment


              #7
              81 is kinda different than a 91. Carb vs EFI, and since you mention kliks I'm guessing Canada so probably no emission BS. that really sounds like a misfire, probably not an engine fault but ignition problems would be my bet. Distributor advance not working right, bad wires, bad plugs, weak coil, something in that range. The off idle hesitation could be vacuum leak or carb problems. Without having a clue about the condition of the parts its really a guess as to what ails it so you really need to verify that the basic fuel and spark parts are in good shape first and go from there.
              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 grandpa spec white and cranberry

              1984 Lincoln Continental TurboDiesel - rolls coal

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

              Comment


                #8
                I just drive it as is, the engine has lots of blowby so I'm done putting money into it, plus I work on cars all day at work so I don't have much desire to work on my own on my days off or after work.
                I put new plugs in it, plug wires are only 2 years old, cap, rotor and distributor is only 2 years old and the coil is 2-3 years old, I get 21hg on my vacuum gauge at idle and the Holley 4160 I have is 3 years old with only around 20 000km driven with it
                Last edited by Not A Midget; 01-15-2018, 12:25 PM.

                Comment


                  #9
                  Update for my post, but I don't think it will help Needlestick very much.
                  I just put in my fairly new ICM from my old 79 Thunderbird and that made things way better. I still have the original Duraspark ICM in my Lincoln, so I thought that might have been the culprit since all other ignition components were way newer

                  Comment


                    #10
                    Ignition/tune-up is definitely worth going through. Plugs/wires, etc and see what it does. Cheap way to possibly fix it.

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