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Thread: Chrysler ODBE-I Piggyback Tuning Help Needed

  1. #1
    Carb and Points! RattleTrap's Avatar
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    Chrysler ODBE-I Piggyback Tuning Help Needed

    First a little background

    I have a 1984 Jeep with a mildly built 4.2L (258 CI) L6 with a Mopar Performance Speed Density MFI (basically a 1994 4.0L MFI). The build consist of 40 over pistons, Howard street/torque cam, and minor head work. I am tuning the MFI system using the Split Second PSC1-003 signal calibrator to intercept the MAP 5V output signal and modifying the signal voltage before it is sent to the ECU to compensate for the lower than stock vacuum. I have added a wide band O2 sensor attached to an AFR gauge along with a sophisticated data logging system - a note pad & #2 pencil. Using the R4 software I have managed to significantly improve the performance the Jeep - better start & idle, more torque, smoother/crisper throttle response, reduced exhaust smell, and slightly improved fuel economy.

    However I am unable to solve one issue - bucking at low speed under certain trail conditions. If I am rock crawling where the engine is put under heavy load followed by lighter load and I go to accelerate the AFR gauge will "peg" the needle to LEAN then swing to the other extreme reading on the gauge - RICH. It will then go into a ever increasing swing back and forth of LEAN-RICH-LEAN-RICH-LEAN-RICH.... until I disengage the clutch and "blip" the engine. At that point everything is back to normal. This only occurs at few hundred rpm above idle - say 1,000 - 1,100 rpm. It also only occurs when I have been running under these conditions for a few minutes, say 4 or 5 minutes.

    I have replaced all of the sensors (TPS, MAP, IAT, Narrow band O2) with no change in the behavior.

    My first question is, is this something I should be able to tune out of the system or is this the nature of the early Chrysler ECU/MFI systems? I do not know if this stock behavior as I installed the Mopar (HESCO) MFI after rebuilding the very worn engine.

    My second question is, I'd like to be able to log key data from the ECU while operating the Jeep. I have found the BoostButton website site and their logging software MP SCAN but I unable to find a USB to SCI cable that will connect to the 6-pin ECU data port. My question is, does anyone know of a source for the cable & connector or have instructions on how to make one?

    Thank you in advance for your help.
    1984 Jeep CJ7
    4 Lift on 33's

    4.2L w/HESCO MFI & Howard Cam
    T-5 & Dana 300
    Spartan Locker

  2. #2
    Carb and Points!
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    Quote Originally Posted by RattleTrap View Post
    First a little background

    My second question is, I'd like to be able to log key data from the ECU while operating the Jeep. I have found the BoostButton website site and their logging software MP SCAN but I unable to find a USB to SCI cable that will connect to the 6-pin ECU data port. My question is, does anyone know of a source for the cable & connector or have instructions on how to make one?

    Thank you in advance for your help.
    Did you find this page:http://www.boostbutton.com/turbonato...=sci_tech_info

  3. #3
    Fuel Injected! steveo's Avatar
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    i tried a PSC once, one problem is that you're adding or subtracting vacuum to affect VE at the same time that you affect timing. this results in you adding fuel by increasing perceptible load while unavoidably removing timing advance. this reduced timing requires different fueling. in short, you're fighting your own tuning the entire time...

    just throwing that out there

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