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  1. #1

    Default Mysterious 8.1L Throttle Issue

    We have a pair of ~2007 8.1L MPIs in our 1971 Magnum. They have been really solid to date. However, we've had one really odd issue occur recently on our starboard engine.

    When increasing RPM through 2,500rpm or decreasing from 3,000rpm cruise rpm through 2,500rpm, the engine RPM will suddenly the engine will drop to idle and lock the throttle out. Meaning the throttle cable continues to manipulate the throttle on the engine but no electronic throttle response from the engine. Otherwise said the throttle will remain at the 2,500rpm position but he engine will be idling.

    When throttling up, if you make it through the 2500rpm threshold, she will run beautifully. No signs of any mechanical issue with the engine. 2,500rpm also seems to coincide with a timing/ignition shift.

    Restarting the engine immediately brings back normal throttle function, so seems like it may be an electronic gremlin.

    Any thoughts on what this might be?

    Thanks in advance for any ideas.

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    9,204

    Default Re: Mysterious 8.1L Throttle Issue

    my guess is both engines have the digital throttle control hardware installed? Also, do you know which ECU you have? Also, any of the optional controls installed - like perfect pass or the cruise control systems? finally, do you have a MIL and does it illuminate when the fault occurs.

    Honestly, I believe the fastest way to resolve the issue is to get a laptop with the RINDA software and the interfacing cable, especially with the newer GCP<CANBus-based> ECUs...without that, the easiest thing is to inspect and reseat all of the cable connections involving the DTC components...

  3. #3

    Default Re: Mysterious 8.1L Throttle Issue

    Thanks for the reply! The throttle itself is not electronic. Standard throttle cable to the motor, where the signal is converted to electronic control. I will figure out which ECU we have, no other electronic throttle controls in the system. No MIL. I will check the connections. Risers were replaced end of last year and will see if any of the connections were jostled.

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