Not this carp again.
The fact my fuel pressure sensor wasn't reading below 62 psi was troubling. Was my fuel pressure regulator not working? Was the return line restricted? Was the calibration on the sensor bad or was it the sensor itself? The sensor works fine from 62 psi and up but not below. I want to have my instrumentation working before I go to the track.
I cobbled some fittings together and put my mechanical fuel pressure gauge in the feed line. Yep, 62 psi. Pulled a light vac on the regulator, yep, pressure went down. Put a light amount of pressure on the regulator, yep, pressure goes up. Something is wrong with the sensor. Plug 500 PSI lowdoller sensor destined for the clutch line in fuel pressure port. Still stuck at ~350 psi with new calibration. Hmm. Check voltage output on hptuners and it never goes below 2.92v.
Check 5V and ground to the sensor, yep. Remove feed wire from sensor to PCM and check voltage, sensor works. Something in the PCM.
I WAS using the fuel level sensor input for the pressure sensors. I assumed it was a 0-5V input based on the voltage range that GM listed on the fuel level sensors (1-2.5V for a tahoe). I think it's actually a 5 v output with current limited supply and the change in resistance in the fuel level sensor changes the voltage out and that's what it reports to the dash. I was trying to input voltage into a supply. Driving the wrong way down a one way.
My rough assumption is the internal resistance of the lowdoller sensor somehow is equal to whatever ohm rating corresponds to 2.92 volts of supply from the PCM. I just got lucky that it was roughly in the range of operation. Once the sensor went over 62 psi it started outputting more than 2.92V and it no longer became a sink and a instead a supply so thats why HPtuners made sense above 62 but not below. It took my electrical engineering buddy to work through it with me and grasp the idea.
I hooked the fuel pressure signal to the fuel tank pressure 0-5v input and it works. I just gotta clean the wiring up and its good. I have to find one more 5v open input for the clutch. Probably the AC pressure switch, red #14.
#stockPCMlifebro
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