This car came back yesterday with the exact symptoms as before & during a road test I quite confidently told the owner that it could not be the same problem, as I had left the barometric sensor unplugged. Wrong again!
This time with IDS to play with I looked at data logging & sure enough there is a baro reading of 688 mb & a check of the sensor showed it to still be unplugged. I also noted some erratic data too. Such as a small VSS (vehicle speed sensor) signal, which increases along with RPM. I have even unplugged the VSS & it is the same. Also the speedo does rise consistent with live data.
I can only reset the PCM by disconnecting the battery for 10 minutes or so & the Baro reading defaults to 1.1 bar. As soon as I plug the sensor back in, the value gradually shifts back down to 0.68 bar, so that proves that the PCM is acting on info from that sensor. A scope trace of power, ground & signal from the Baro sensor has been checked at the sensor & PCM & both look good.
I also have an “OD Off” green light flashing & the transmission ECU is showing a transmission fluid temp sensor fault. I don’t think this was doing this before I plugged in. Oh I nearly forgot, I did do a PCM calibration update while I was in there.
One possibly vital point I may not have mentioned before, is that a couple or so years ago, this motor suffered the common problem of the wiring harness dissolving in the valley of the head, to the ignition. We made a loom up ourselves & now I am wondering if some issue with that maybe causing a spurious signal to reach the PCM, causing the invalid VSS signal.
Sorry for the life story!
Any comments welcome.
Regards
Dave
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