Erratic TPS/MPH readings
03-05-2006, 01:53 PM
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Car: 1987 Monte Carlo SS
Engine: L98
Transmission: 200-4R
Axle/Gears: 7.625 10 bolt/3.73s
Erratic TPS/MPH readings
First off, the car is a CCC to SD swap. Overnight, the car went from running great, to so rich that it won't even run. Constant smoke out of the exhaust and pitch black plugs. I hooked up my scanner and saw some pretty crazy stuff. Key on, engine off, TPS disconnected; my ALDL is reporting voltages ranging from 2v to 3.5v. At the same time, my VSS is showing MPHs from 0-230mph, hovering around 215MPH. All my other readings are normal, so I pretty much ruled out a TPS grounding issue as the CTS and MAT are grounded from the same wire, but I checked them all anyway and all were under .5ohm from the engine ground point. I don't even know where to start with the crazy MPH readings. Any ideas what I am experiencing here? Are the erratic TPS/MPH related, or separate problems? Thanks for any input.
03-05-2006, 02:08 PM
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Car: 1987 Monte Carlo SS
Engine: L98
Transmission: 200-4R
Axle/Gears: 7.625 10 bolt/3.73s
I checked the TPS with a DVM at the ground and signal wires, and got a voltage hovering around 2.8v. Unplugged the TPS on my Bonneville and checked the ground and signal wires on it and got nothing, so the fact that there is any voltage at my signal wire with no TPS connected is a problem.
03-05-2006, 04:11 PM
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Car: 1987 Monte Carlo SS
Engine: L98
Transmission: 200-4R
Axle/Gears: 7.625 10 bolt/3.73s
I was thinking the same thing, but was unsure because all the other values were good. After raiding a 3.1 sunbird for a 7730 in the junkyard, the car is running again, thanks for the input 406.
03-08-2006, 08:30 PM
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Car: 2009 Pontiac G8 GXP
Engine: LS3
Transmission: 6L80E
Axle/Gears: 3.27
I guessed right 
Actually, since I have done the '730 swap, I thought that there was some internal voltage leakage with the ECU...especially given your readings.
With the engine off, you shouldn't be getting 2.0-3.5 volts on anything...it should be either 5 volts reference, and the sensor input signals would be close to 0 or close to 5 volts depending on the sensor...
Glad to hear it fixed the problem...
Actually, since I have done the '730 swap, I thought that there was some internal voltage leakage with the ECU...especially given your readings.
With the engine off, you shouldn't be getting 2.0-3.5 volts on anything...it should be either 5 volts reference, and the sensor input signals would be close to 0 or close to 5 volts depending on the sensor...
Glad to hear it fixed the problem...
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