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Discussion Starter #1
Been working on this issue for several months now and can’t figure out what the heck is going on. Team Camaro has been an extremely valuable resource in helping me work on my car the last 2 years. So I thought I would put the question to the experts here to see if you guys think my logic is reasonable before I spend more money. I have posted this several times on other forums and have not gotten any good answers. I have a GMPP LS3 crate motor with the GMPP E67 controller and harness and a T56 Magnum installed in a 69 Camaro. The 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. I even inspected the pins with a magnifying glass and they all look good.
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 and I am thinking that it is a low side issue with the VSS signal in the ECM. I am thinking this because the speedo continues to work with the high side VSS signal because the speedo is internally grounded.
Before I spend the money to buy a new ECM I wanted to see if you guys think my logic is reasonable or if anyone out there has any ideas. It’s just that it seems like a mechanical issue somewhere and not an electronic one. Would really appreciate some help on this. Thanks.
By the way here is a link to some pictures of my car -
http://www.forgeline.com/customer_gallery_view.php?cvk=911&car_model=Camaro&car_make=Chevrolet&offset=40
 

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Discussion Starter #2
Did not get any feedback so thought I would follow thru with my next steps. I am currently looking for an unmolested GMPP E67 controller. Then I will replace the ECM with the new one with the factory GMPP tune. Hopefully it will run enough to see if the problem is corrected. If the problem is corrected then I will flash to the custom tune and see if the problem re-appears. If not then the ECM was the issue and if it re-appears then the tune created the problem. Sound reasonable?
 

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I'm no expert on these systems when it comes to gremlins but I would be taking the exact same approach as you are.
 

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Discussion Starter #4
I appreciate the comment. I am not an expert either but the one good thing about this whole exercise is that I have learned more about how the ECM works. I have been following your build thread and am curious if you wired your ECM per the instructions and are using the reverse inhibit feature also?
 
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