GMPP E67 Controller, P0507 Code, and Speedo Calibration Issue Fixed
I am writing up this summary to provide a solution that might help others that may have the same problem. First some background. I have a new GMPP LS3 crate motor with the GMPP E67 controller and harness installed in a 69 Camaro with a T56 Magnum transmission and a Moser axle with a 3.42 ratio. Within a day of getting it running and back on the road I kept getting an intermittent P0507 Idle Speed High code. I also discovered that the reverse inhibit function was also intermittent. I need the controller to be consistent for the reverse inhibit feature to function correctly because it is darn scary to shift at 70mph and it goes into reverse instead of 5th.
I rechecked the wiring and confirmed I have the VSS connected to connector C3 pins 66 and 67 and the Speedo is connected through the bulkhead connector pin D as per the instructions. After several months of frustration and changing parts and harnesses I finally bought HPTuners to help me troubleshoot the issue. I was monitoring it with HPTuners and discovered that the engine controller intermittently loses the mph calculations and when I am running at speed I get the P0507 code and the reverse inhibit stops working. What is strange is that my electronic Autometer Speedo still worked great and fairly accurate this whole time.
I also discovered that when the ECM loses the mph I could stop, put it in reverse and back up about 15 to 20 feet, put it in 1st gear and drive off with the ECM working correctly for a mile or so then the ECM loses the mph again. The lost mph would happen if I was moving or sitting at a stop light. I could not discover a trigger for the event.
After changing the VSS, connectors and harnesses I concluded it was a possible bad ECM or a bad ‘tune’ to the ECM. Unfortunately someone else did the ‘tune’ to the ECM and I did not have a copy of the factory configuration so I could not reflash to the stock configuration.
So I got a new E67 controller with the same part number as the original and replaced the custom tuned controller. Engine started up right away at first crank. Drove for about 50 miles and did not lose the mph in the controller at all. The mph was running really slow but the controller had a steady mph reading the entire time.
So I thought I had confirmed the original ECM was bad so I’ll just change the speedo parameters to match what I have, reflash the new ECM, and away I go. So under the speedo General tab in HPT Editor I changed the VSS pulses per revolution from 40 to 12 for the T56 Magnum transmission requirement, and under the Gear/Tire Calc tab the rear axle ratio to 3.42, and the tire diameter to 25.2. Did a calibration flash and the Speedo was dead on relative to a Garmin GPS and HPT Scanner within less than 2 mph relative to the GPS. Issue fixed….for about 1 mile. No happy dance yet, same issue with the ECM with no mph indicated.
Did some experimenting and discovered that the trick seems to be to NOT change the factory VSS pulses per revolution but keep it at 40.0000, the stock configuration. The math relationship has to be a linear equation so what I ended up doing was dividing the final axle ratio by the ratio of the VSS pulses or in my case
3.42 axle ratio/(40 ECM VSS pulses per rev/12 Trans VSS pulse per rev) = 1.026 corrected axle ratio
Went and edited the configuration under the Gear/Tire Calc tab to the 1.03 ratio and 25.2 tire size, hit the commit button, reflashed the ECM. I had to round up the corrected axle ratio from 1.026 to 1.03 because the table would only accept a 2 decimal point number accuracy.
Bingo, the speedo, ECM, and GPS all read correct and the same and have for over 109 miles now with no issues. No drop off of the mph in the ECM, so happy dance time.
Went back and reflashed the original ECM to the same parameters and bingo, no more problems. Now I have a performance ECM and a cruising high MPG ECM that both work reliably.
I can’t explain why it works and the 3.42 ratio that is the default configuration in the ECM seems to be very misleading on GM’s part. I read several posts on various forums that commented this is one area GM is horrible at calculating.
Hope you find this of use if you have similar issues.
Bruce L
