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Code 91 on 88 grand marquis

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    Code 91 on 88 grand marquis

    Hi there! I have a 88 grand marquis that i recently rebuilt the engine in school about 10,000 miles ago and its been having some problems. it would never quite run like it should've and i hooked a code reader up and one was that the tps had low voltage, tested that and came back bad so I replaced the sensor and it cleared that code, did another KOER test and codes 33 and 91 came up. I'm not sure how serious 33 is for the egr valve but 91 is really bugging the crap out of me. the car has a very rough idle when warm and idles up and down quite a bit. out on the road i have no problems though. also replaced the fuel filter a couple days ago thinking it would help because i had no idea the last time it was changed but it didn't help anything. Any input would be appreciated!!! Thanks!

    #2
    91 is lean bank 2 (which is the drivers side I think since that side is cylinders 5/6/7/8). So it's seeing a problem that's only affecting that side. Check for vacuum leaks.

    Code 33 is EGR not working properly. Make sure all vacuum lines for that are hooked up and not broken. (brittle plastic lines)

    I'd also check the basics. I'd check to see if the timing is at 10btdc with the spout connector disconnected.

    Disconnect the IAC and see what the base idle is when warmed up, it should be between 650 to 850. (Check to make sure you don't have vacuum leaks before adjusting the screw on the throttle body). Once that's been verified, adjust your TPS so it's at .900V at closed throttle (it's not necessary to have the engine running to adjust the tps, just have the key in run).

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      #3
      i've done all the checking i can for vacuum leaks because thats what i thought it was too. i hooked a smoke machine up and found a couple lines that were leaking, so i fixed those but it didn't fix any of the problems. i also forgot to mention that being in a hurry when we put the engine in, i forgot to put plugs in the back of the heads where that tube originally was that lead to the air pump, so it has exhaust leaks on the back of the engine. could this cause the o2 sensor to read that its lean? and i'm about to go check the tps voltage and timing now

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        #4
        Originally posted by 88mercgrandmarq View Post
        i've done all the checking i can for vacuum leaks because thats what i thought it was too. i hooked a smoke machine up and found a couple lines that were leaking, so i fixed those but it didn't fix any of the problems. i also forgot to mention that being in a hurry when we put the engine in, i forgot to put plugs in the back of the heads where that tube originally was that lead to the air pump, so it has exhaust leaks on the back of the engine. could this cause the o2 sensor to read that its lean? and i'm about to go check the tps voltage and timing now
        Yes. It most certainly can. What engine are we talking? A stock Grand Marquis engine rebuild? Did you do any performance upgrades?

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          #5
          it has a 5.0 out of a 91 crown vic that I just rebuilt stock, the only things I did different is I put on dual's and removed the air pump upon reassembly. how would i go about plugging those holes in the back of the heads?

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            #6
            Originally posted by 88mercgrandmarq View Post
            it has a 5.0 out of a 91 crown vic that I just rebuilt stock, the only things I did different is I put on dual's and removed the air pump upon reassembly. how would i go about plugging those holes in the back of the heads?
            I think the way to do it is 5/8" coarse thread bolts. I think that was the size (it's a bitch to find I hear). I didn't have that problem since I have GT40p heads.

            The other way you could do it is reattach the pipe and just plug it at the end.

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              #7
              do you have any ideas on a simpler way to put the pipe on without having to remove a bunch of stuff? i also adjusted my tps to .9 volts

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                #8
                the pipe will shimmy in from the passenger side (done on my 88 MGM). distributor wrench works like a charm to tighten the bolts down.

                the other option is to make a couple of 1/8" steel slugs to cover the holes and bolt them on. The other option is to cut the pipe and put the ends on the wrong sides to cover the holes.

                Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                Originally posted by gadget73
                ... and it should all work like magic and unicorns and stuff.
                Originally posted by dmccaig
                Overhead, some poor bastards are flying in airplanes.

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                  #9
                  Did you retorque the lower intake manifold after 20 minutes of runtime? You're supposed to retorque. While you're in there, you can put the pipe back on.

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                    #10
                    thanks for all the help everyone!!! I'm gonna put the pipe back on this weekend and plug the end of it, I'm really hoping this will fix my lean issue

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                      #11
                      Let us know how you make out!

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                        #12
                        she works perfect now!!! thanks for the help guys

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                          #13
                          Glad to hear!

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