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Thread: Sensor Readings Are Offset/Incorrect

  1. #1

    Default Sensor Readings Are Offset/Incorrect

    Issue: Just as the title says, all sensors readings are incorrect without engine running (voltage: 20V, fuel pressure: ~ 48 psi, TPS: 100%, temp: 0°, oil pressure: 100 psi, etc.). The 5V reference reads 4.9V and inputs from sensors appear correct (for example, fuel pressure input is 0.5V), but ECU is displaying incorrectly. Everything was working fine for over two years. Truck was not driven for a while and I had to remove and charge the battery. Upon reinstalling battery, it appeared as if no tune was loaded. I upgraded the ECU to V5 from V4 and reloaded the tune. Everything was fine for a few short drives, then it went haywire and died while driving.

    What I've tried: I have replaced all grounds (battery-frame, engine-frame, body-frame) and relocated ECU ground to engine. ECU power/ground is, and always has been, direct from battery. I contacted Holley support and was told the tune being wiped could be due to switched 12V power not shutting off cleanly. This turned out to be true, due to a MSD noise filtering capacitor that was backfeeding voltage for a couple seconds after ignition was turned off. The cap has now been bypassed and power to ECU shuts off cleanly.

    Subsequent attempts to contact Holley support resulted in them telling me my hood was creating EMI and needed to be grounded. Admittedly, I have not grounded my hood, there's no way that's the issue. ECU was then returned to Holley who could not find anything wrong with it. Upon receipt of ECU from Holley, it worked for a few starts, then reverted to the incorrect sensor readings.

    Setup:
    BBC
    Dominator ECU
    Firmware V5 build 110
    Terminator Throttle Body
    4L80E
    Large Cap HEI (No Ignition Control)

    I'm at a loss as to what to do now. If anyone has any suggestions or has seen a similar issue, please let me know.
    ECU is obviously out of warranty, and I really do not want to have to buy another hoping it will correct the issue.
    Thanks in advance for any insight.

  2. #2
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
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    I don't have personal experience with this ECU, but when 5V sensors go full scale or read high, the ground which might be a common ground to a few sensors has gone open circuit. Gary
    Regards, Gary

  3. #3
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,081

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    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  4. #4

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    Quote Originally Posted by Gaz64 View Post
    I don't have personal experience with this ECU, but when 5V sensors go full scale or read high, the ground which might be a common ground to a few sensors has gone open circuit. Gary
    That was my first thought. Even though all appeared to be grounded, I moved the sensor ground wire to a new location and replaced the battery cables, engine ground, and cab ground to no effect.

    Quote Originally Posted by Danny Cabral View Post
    I did not mention it above, but I have disconnected each sensor individually while monitoring the gauges. The only change is the reading of the sensor I disconnect. I may go through this exercise again while taking notes to make sure I did not miss anything.

  5. #5
    Join Date
    Jan 2010
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    Brisbane, Australia
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    I had a F350 in limp mode logging 5V3 reference codes. This 5V goes to MAP, IAT, brake pedal, and one other, (which escapes me now).
    The 5V at the MAP read 3V with a meter, disconnect IAT, still 3V, eventually get to the brake pedal sensor (BPPS), now 5V at the MAP.
    Ended up being the 5V ref to the BPPS, shorting to ground within the dash framework, microscopic pinhole from an unprotected sharp edge.
    3 hours, 15 minutes to fix. Gary
    Regards, Gary

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