{"id":842,"date":"2017-11-14T15:35:00","date_gmt":"2017-11-14T23:35:00","guid":{"rendered":"http:\/\/automobileman.com\/wp\/?p=842"},"modified":"2017-11-22T18:05:03","modified_gmt":"2017-11-23T02:05:03","slug":"gen-v-lt1lt4-vss-signal-generation","status":"publish","type":"post","link":"http:\/\/automobileman.com\/wp\/?p=842","title":{"rendered":"GEN V LT1\/LT4 VSS and tach signal generation"},"content":{"rendered":"

I’ve had quite a few inquires lately in regards to how to power and drive your conventional mechanical or electronic speedometer from the new GM 8L90E 8-speed transmission.\u00a0 After talking at length with GM Performance and Powertrain they have provided a few solutions that should work.
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\n<\/span>The 8L90E transmission is a second-generation model that uses an electronic controller built within the transmission itself.\u00a0 If you’re using the GM “Connect and Cruise”<\/em> system it includes a separate controller (black rectangle with blue connector above right) that communicates back and forth between the engine ECU and the transmission itself.\u00a0 This system is part of the CANBUS or GMLAN electronic control system and is for all practical purposes standalone, they don’t want you piggybacking off the system because you can potentially disrupt the network transmission protocol.\u00a0 For the 8 speed automatic transmissions, the vehicle speed information is fed to the transmission controller through a pulse signal. The Vehicle Speed Sensor connector (on the wiring harness) is not used because there isn’t one on the 8L90E to plug into (see below).\u00a0The ECM is programmed and looking for 40 pulses per revolution.<\/span><\/p>\n

I have successfully piggybacked off the VSS signal from a T56 manual transmission<\/em><\/strong> and generated the correct speed using the Dakota Digital VHX gauge package<\/a> with their BIM 01-2 module.\u00a0 Using the VSS signal from an ECM requires a single wire input into the Dakota Digital bus.\u00a0 Since the signal is generated outside the GMLAN, a simple pulse generated inductive signal from a magnet, I believe it doesn’t disrupt the signal going to the ECM (see my LT1\/LT4<\/a> installation guide for more guidance).\u00a0 This is necessary because both the LT1 and LT4 Gen V engines require a VSS signal, without one they go into ‘limp mode’<\/em><\/strong> and run at 1\/3 throttle. Set up this way my engine and transmission function correctly because they do not generate any check engine codes or MIL lights.<\/span><\/p>\n

GM Powertrain recently brought to my attention that pin 14 (grey\/blue wire) out of the transmission will provide a non-CANBUS raw signal (pulse generated) that should drive a conventional electronic speedometer. This is an inductive type signal so voltage output is dependent on speed.
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This is the plug that connects to the 8L90E transmission, if you look closely you can see the grey wire.<\/span><\/a><\/span>
\nThe plug goes into the transmission here.<\/span>
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One sim<\/span>ple solution available is a conventional shaft <\/span>mounted VSS signal\u00a0<\/span>generator like this:
\n<\/span>Summit Racing sells\u00a0<\/span>this part:\u00a0https:\/\/www.summitracing.com\/parts\/dak-sen4165\/overview\/.\u00a0This is a VSS mag<\/span>net kit with pick up coil. Normal rear wheel drive domestic installation takes four magnets on the drive shaft with a pickup coil mounted approx 5\/8″ away.\u00a0 It seems odd that you would use old school mechanical magnets spinning around on the outside of your driveshaft to get a signal that your speedometer can read, but it’s a least a solution.
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A little bit mo<\/span>re elegant solution is this split-collar speed-sensor that is used on data-acquisition systems
\n<\/span>Another option is a GPS driven signal like this:<\/span><\/p>\n

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\nThe best solution seems to be the recently released STA-100 ODBII interface that not only handles the speedometer issue, but also provides a tachometer signal.\u00a0 There is also pin C (white wire) output from the bulkhead connector on the GM wiring harness that provides engine speed, but it’s a CANBUS signal and will not drive an aftermarket electronic tachometer unless it’s OEM.<\/span><\/p>\n

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The\u00a0STA-1000\u00a0<\/strong>plugs directly into the OBDII diagnostic connector, providing a user-adjustable traditional Speedometer, Tachometer and Check-Engine output for your choice of aftermarket instruments.<\/span><\/p>\n

Features:<\/strong><\/u><\/span><\/p>\n