Need Help Trying to Understand How VSS/ECM Works to Fix a Problem
11-16-2014, 02:52 PM
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Need Help Trying to Understand How VSS/ECM Works to Fix a Problem Been working on this issue for several months now and can’t figure out what the heck is going on. I have a GMPP LS3 crate motor with the GMPP E67 controller and harness and a T56 Magnum installed in a 69 Camaro. ECM has a tune and runs great with mostly single digit LTFT’s. However, I keep getting an intermittent P0507 Idle Speed High code and the reverse inhibit feature stops working. To help me troubleshoot the issue I have been monitoring it with HPTuners and discovered that the engine controller loses the VSS signal and when I am running at speed I get the P0507 code. What is strange is that my electronic Autometer Speedo still works great. I have ohm’d the wiring and confirmed I have continuity and the VSS is connected to connector C3 pins 66 and 67 and the Speedo is connected through the bulkhead connector pin D as per the instructions. This past week I built a new jumper harness with new connectors to connect the VSS directly to the ECM by-passing the GMPP harness and replaced the VSS with a new one. Still have the issue. Monitoring with HPTuners I discovered that when the ECM loses the VSS signal I can put it in reverse, back up 15-20 feet and the mph read out in HPTuner will bounce up to 4-6 mph then down to zero, then put it in 1st gear and drive off with the VSS working correctly. Until it stops working again which can be anywhere from ½ mile to 20+ miles later. I have done the ‘reverse’ trick about 20 times now and each time the VSS will work correctly for a period afterwards. I need the speed signal in the controller to be consistent because it is darn scary to shift at 70mph and it goes into reverse instead of 5th. The only component that I have not changed is the ECM but before I did that I wanted to see if anyone out there has any ideas. Would really appreciate some help on this. Thanks.
11-16-2014, 03:33 PM
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Could not find a GM speed sensor that would fit. According to Tremec I should be using the Ford sensor so that is what I have been using. Any other ideas?
11-17-2014, 06:47 PM
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A bit difficult to measure but I got the diameter of the hole at .930 and the depth to be 1.20. Not sure how to measure the gap. Are these dimensions sufficient for what you wanted? What did you have in mind? Thanks for the help.
11-20-2014, 06:11 AM
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Isn't the Ford sensor a different pulse per mile than the Gm? Doesn't it have to be reset in the tune? IIRC it does. IF you haven't changed it, that could be your issue because it would be out of range of what the ECM is looking for.