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2.8L Missing/Shaking when warmed up

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  • 2.8L Missing/Shaking when warmed up

    I've got my 2.8L Regal Custom with 109K + ?? = ?? miles (broken odometer) and I'm having some problems.

    I bought the car about a month ago, and when I got it, it was running pretty good, but I was getting some hesitation and the engine was missing when I was cruising on the highway at a constant speed (under acceleration it seemed to be fine). It also was kind of "bogging" down right after starting, and then recovering to a normal idle. Naturally, I figured a tune up was in order.

    Not looking to spend a ton of money, I went out and bought some things for the tune up: A bottle of Lucas Fuel Injector cleaner, AC R44LTSE plugs, Autolite professional wires, a fuel filter, and a PCV valve (which I still haven't gotten around to installing).

    I did the FI cleaner and the fuel filter right away, then just two days ago I got around to doing the plugs. The old plug wires were of various brands, but the same AC R44LTSE plugs came out. They all looked to be in pretty good shape, no unusual wear on them. After much swearing I finally got the wires off the rear plugs, and put the new ones in using anti-sieze, gapping them to .045, and torquing them to the factory spec of 24Nm (as listed in the factory service manual) then attaching the wires directly (in retrospect I should have pulled the boot back, attached the wire, then slid the boot back over---I'll probably be doing that tonight ). The only glitch I noticed when doing the job was there was a touch of corrosion on one of the contacts of the coil pack for cyl #4, I believe. I just connected the wire anyway, and when I ran the car it didn't seem to be missing or having other problems, so I shurgged it off.

    The next morning, when I took the car to work, I had no problems getting to work, the car was running much smoother, it started and idled great when cold, and overall performance seemed to be much improved -- the constant speed hesitation was gone. I was very happy with the results. However, on my way home, I made a few stops and was driving for a longer time--giving it enough time for the engine to get hot. The car started to miss and shake consitantly with constant speed (something it only did occasionally before hand) and stalled three times on the way home. When I sit with the car in park, and hold the revs at ~2500 (no tach, so can't tell you exactly), it revs up to speed ok, but as I hold it there, it starts to sputter and miss, after 5 seconds, it is missing badly and shaking violently, however, when cold, no problem.

    I'm going to check all the plugs, make sure the torque spec is OK, and clean off all the contacts on the coil packs tonight. I don't think its some kind of contact problem with the plugs--since it runs fine when cold. The only thing I changed since the problem began though is putting the new plugs and wires in, so nothing else has really changed, and I don't know what else to blame. I'm pretty much just looking for ideas on what could be causing this. I want to try and fix it ASAP, as I planned on taking the car on a 600 mile trip this weekend.

    Thanks for your help in advance.

  • #2
    maybe your coil has internal problems. I had a problem like that with an msd coil. Worked fine when I put in a new coil (accel). I also had a miss that I just couldn't get rid of once. I put in new everything, no help. Then I did a cam swap and presto, it was fixed. I measured the cam lobes and man were they different from lobe to lobe (worn out) good luck on that one though
    Why pay someone to do the work, it costs alot and you don\'t learn s*^t!!!

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    • #3
      Thanks for the tip, I'm afraid it might be the coil packs as well, but I'm going to change the O2 sensor on a gut feeling anyway before I start messing with the coils. I'm very doubtful its the cam, since it would be missing all the time, and not when warm. Plus, I don't want to do a job like that on this car, if I'm going to go through all that trouble, I'd just drop a 3100 in there.

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      • #4
        Turns out my gut feeling was right, finally was able to get a code out of the car -- code 44, O2 sensor reporting lean condition for more than 60 seconds. So what has been happening, is the O2 sensor keeps reporting a lean condition while the PCM continuously adds more fuel, causing a very rich condition--causing my problems and my poor fuel economy.

        Tomorrow I'll make a stop at Advanced Auto and grab a new sensor and slap that in there, and hopefully it should be good to go.

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        • #5
          New Bosch O2 sensor is in, and the engine seems to be running at a 200% improvement. Took it about 7 miles, filled it up with gas (it was running so bad I used 8 gallons in 2 days!!) revved it in park for a bit, engine seemed to hold its speed fine, didn't want to miss/stall. Drove it home hard, really gave it a work out, revved it to speed again in the driveway--held speed smooth and just seemed to be running well. The car drives smoother, doesn't act weird when I feather the gas to maintain speed now, which is important and has been bugging me like crazy. Also, doesn't reek of unburned fuel after I turn it off and get out. Oddly enough, when I floor it, it seems to have lost a little power, but I can deal with that for the (hopefully) restored fuel economy.

          Annoyingly enough, I am still getting a bit of a shudder when I am running at a constant speed of 50+ sometimes, so that might actually be a torque converter problem. Sucks, because I'm not going to start fucking with that, and if necessary I'll drive the car in D.

          Install wasn't bad either, after I used 9" worth of extensions, one swivel joint, and a 5 foot pipe to help me get the old O2 sensor out.

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