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Thread: Rough idle and code 51

  1. #1
    Hybrid booster
    Join Date
    Jan 2007
    Marietta, GA

    Rough idle and code 51

    86 Shelby Charger converted to 87 electronics with 87 glhs stage 2 pcm. 4 wire O2 conversion. Wastegate hooked straight to intake boosting 8-10 psi and currently no intercooler installed. Just trying to work bugs out before I plumb intercooler. Last summer the car drove and idled great. On the way home from a car show, it lost power on acceleration. Code 51 popped up and fuel pressure test revealed low pressure. Car sat all winter. Installed a stock replacement Carter fuel pump last week and car drives down road great again. Plenty of power and boosts good. Code 51 still there and rough kind of lumpy idle. Exhaust smells and looks rich, black smoke at idle. Can a bad O2 cause my idle to be rough? Iím going to scope O2 sensor when I get a chance just want to know what else to look for.

  2. #2
    boostaholic Turbo Mopar Contributor
    Join Date
    Mar 2013
    Columbia City, Indiana

    Re: Rough idle and code 51

    Well, the definition of code 51 is O2 sensor lean to long. It says engine allowed to run rich, but prevented from running lean. So yeah, it could very well be your O2 sensor took a dump. Let it idle for a little bit, and check your plugs. If they are black and sooty, you are most certainly running rich.

    Another thing to check is your ignition. Especially the coil if it's original. I have been fighting several issues on my Scamp for the last two months. I believe I had several issues, but the last one was rough idle, and missing going down the road. A new coil fixed it. I guess my original 35 year old coil was finally giving up...

    Just something to check...

  3. #3
    Hybrid booster
    Join Date
    Jan 2007
    Marietta, GA

    Re: Rough idle and code 51

    This car has been on the back burner as Iíve been working 6 days a week all year. I threw a new battery in it today and let it run a bit. I want to chase down this issue. Pulled the plugs to re gap them, they are definitely black and sooty. Either itís running lean and defaulting rich, or I have a bad o2 sensor.

  4. #4
    Supporting Member Turbo Mopar Contributor zin's Avatar
    Join Date
    May 2006

    Re: Rough idle and code 51

    Definitely check the wiring for the o2, but also check the live data for the map and coolant temperature sensor, as well as the tps.

    Tps is a bit of a long shot, but too easy to check to not confirm it's right. The others are the primary sensors determining injector duration.

    As always, check out the hoses, etc for leaks /damage.

    Good luck! It's come a long way from almost dying in the junk yard!

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