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Old 03-02-2015, 08:03 PM   #7 (permalink)
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T-Fitting/T-Valve - See "Water In Fuel Drain"

Tachometer - Device that indicates engine RPM. The signal for this gauge is derived from the alternator. Erratic reading from the tachometer may indicate a possible alternator problem. Follow proper diagnostics before determining if the alternator is at fault. The alternator pulley diameter is specific to the 6.5, so the wrong alternator pulley size will effect reading of tachometer as well.

TCC (Torque Convertor Clutch) - PCM modulates lockup according to requirements, Brake switch releases control. The TCC locks up under several conditions: brake switch off, engine temperature and speed. If your engine fails to meet these criteria, the TCC will not lock up.
  • If you would like to know how to manually lock the TCC on an OBDI truck Click here.
  • Why not to do the TCC lock up mod by GenBiltstein our 4l80E transmission guru Click Here
TDC Offset (Top Dead Center Offset) This is a factor the computer uses to compute timing for fuel injection.Theft Deterrent Learn - Click here for procedure for an OBD-II.

  • Recommended Brands: AC Delco or Robert Shaw. Part numbers found in the 6.5L Parts List. All other aftermarket brands openings are too small for adequate coolant flow.
  • 180*F Thermostat - Pros & Cons Discussion Click Here
  • No Thermostat - What Are The Risks? Click Here

Throttle Position Sensor (Not APPS) - How to test and adjust the TPS on a pre 1994 truck Here

Torque Specs - Common Engine, Transmission & Differential Torque Specifications Click Here.

Towing - Many people tow with the 6.5. It may have its limits, but it makes for a decent truck.
Transfer Case
Transmission - Automatic - To get help with your automatic transmission:Transmission - NV4500 Transmission - Other GM Manual Transmissions Turbo - turbocharger) - The device that makes boost (more air pressure to the intake of the engine) from exhaust gas energy. See this thread.
(See also Wastegate for more information. Both are related)
  • To increase boost for the vacuum wastegate system see "Boost Fooler".
  • Information about the GM-X Turbo size can be Found Here.
  • Rebuilding the GM-X Turbo Found Here
  • Rebuilding the GM-8 Turbo Here

Turbo Heat Shield - Info and pictures Here

TurboMaster - a spring-operated wastegate controller that uses spring compression rather than vacuum to control turbo boost output. You can buy one at Heath Diesel, Kennedy Diesel, or make your own. They are all the same in principle, but different year trucks look different, so here's a few examples:
  • 1992-1993: GM3 turbo. Example here
  • 1992-1995: front-facing. Example here
  • 1996-2000: vertical. Examples here or here
TurboMaster Spring Rate- For the weight of spring to use on a Turbomaster Click Here.




Vacuum in Fuel Tank - Excessive vacuum in fuel tank is not a good situation. see Fuel cap, or read this thread.

Vacuum System & Pump - Belt driven device that creates vacuum source to run mostly the turbo wastegate system. If your vehicle is equipped with an EGR system, then the vacuum pump also provides a vacuum source for the operation of the valves and solenoids in the EGR system. VSSB (Vehicle Speed Sensor Buffer) - Provides several factored frequency signals to PCM, ABS, and speedometer - divided frequencies are determined by soldered jumpers, to match tire sizing, differential gearing.
  • For information to modify your VSSB for an accurate speedometer, Click Here.

VIN Decoder - Click here


Wait to Start - Glow plug period time. Got no wait to start light? Look under Engine Coolant Temperature Sensor, Glow plug relay, and this thread on Engine Grounds.

Water In Fuel Drain - The factory "T-valve" is no longer available. For replacement options Click Here

Wastegate - The "flapper" valve that opens to bypass exhaust gasses around the turbine, thus reducing Boost to specified and safe level for engine operation.Wastegate Solenoid - the computer operated solenoid valve that regulates the amount of vacuum going to the wastegate actuator on the turbo. This should hold the wastegate shut at idle. Not-so-common troubleshooting ideas to insure proper operation can be found here.

Water Pump - See Engine Cooling

White Smoke - Some white smoke on cold start is normal. It should clear in a few seconds. If the white smoke continues:

(a) If the white smoke smells "sweet" - burning coolant

(b) If the white smoke smells like diesel fuel, there are two possible causes: failing injectors or lift pump. See this TSB regarding the Lift Pump Click Here

Windshield Washer
  • How to troubleshoot windshield washer pump Here
Windshield Wiper Delay Fix - GM wipers have a documented cold-solder problem on their circuit boards, often causing the wipers to stop working.
WMI - Water Mist Injection an alternative to using an intercooler. For more information:
  • Water Mist Injection Install with Pictures: See Here
  • Water Mist Injection Install: See Here




Last edited by Freddyack; 11-26-2015 at 08:09 AM. Reason: Add Carcode TDCO