Diesel Place : Chevrolet and GMC Diesel Truck Forums - View Single Post - Info: The 6.5L FAQ's... The Master List of Information and 6.5 Answers
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Old 08-09-2010, 08:03 PM   #4 (permalink)
Off we go!.......
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Join Date: Jun 2007
Location: Dayton OH
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Fan Clutch - This is a fluid clutch that controls the engine fan. it reduces fan noise and increases fuel economy. Feed the Beast - This is a modification to your filter manager. It will increase the fuel flow though the filter manager.
Fish Biting - (or fishbiting) This is the description for when the engine may "miss" or may not fire properly for a very brief instant. As always, do not rule out fuel supply issues with lift pump, OPS, and take a look at PMD. Remember to do as much diagnostic work to prove out all parts that are at fault.

Flex Plate - flywheel for the 4L80E - How to change a flex plate, step by step. In this thread.

Flex plate bolts

11589040 or 1261968 - 4L80 Torque converter bolt 6 required

14088764 or 3727207 - flexplate to crank bolts 6 required
GM's description - 7/16-20X .70

Fuel Additives - Diesel engines built before 2007 need fuel lubrication as the fuel systems were not designed to run on ULSD (Ultra Low Sulfur Diesel). There are many additive options from which to choose.
  • Cold Weather Additives & Anti Gelling Here.
  • Lubricity Additive Study Here.
  • Two Cycle Motor Oil Here.
Fuel Cap - Can cause excessive vacuum in fuel tank. Excessive vacuum in a Diesel fuel tank is not desirable.
  • General Information Click Here.
  • Picture and description how to modify fuel cap for better venting Click Here

Fuel Contamination -
  • Gasoline: Accidentally forget what you were pumping? Gasoline can be a very damaging ingredient to cause a lot of failures within the total fuel system. Read This Thread for more information.
  • Algae/Microbes: If you see black spots in your fuel filter manager bowl or on the filter, Go To The Link In This Post

Fuel Drain - aka T-Fitting or T-Valve. See "Water In Fuel Drain"

Fuel Filter - How To Bleed Air Here

Fuel Filter Bowl Contamination - IP's are under warranty for 11 years or 120,000 miles. Replacement IP's after that time are subject to the indiviual's warranty policy. If replacing under warranty check This Thread out.

Fuel Filter Manager (FFM)- This item is what is on the top rear part of the engine valley. It houses fuel filter, water in fuel sensor, and fuel heater.

Fuel Filtration - Filtering Diesel fuel is very important. Fuel can be dirty and the injection pump must have clean fuel to last.
  • Fuel Screen - How To Replace Video Click Here
  • To see an auxiliary fuel filter setup Click Here
  • Parts list for pre filter setup Here
  • For info on the stock fuel filter Click Here.
  • To view a filter setup pre-lift pump Click Here.
  • For info on a Secondary Fuel Filter setup Click Here
Fuel Line leaks - See Leaks, fuel (This causes air to enter the fuel system and may create stalling, hard starting, or fishbiting)

Fuel Line Install Tips On How To Remove/Replace Click here

Fuel Line Size (Stock/OEM) -
  • 3/8" ID from tank to lift pump, from lift pump to Fuel Filter Manager
  • 1/4" ID from Fuel Filter Manager to Injection Pump and T-valve drain
  • 5/16" ID for the return line back to fuel tank
  • 3.5mm injector return line

Fuel Tank Sock - The fuel tank sock provides the first level of filtering to the fuel system. When replacing the fuel tank sending unit it is critical to use the correct diesel tank sock. For more information, Click Here

Fuel Temperature Sensor - Mounted internally, PCM monitors IP fuel temps to determine viscosity and fuel rates.

FSD (Fuel Solenoid Driver) - Commonly known as a PMD (Pump Mounted Driver). This device that opens and closes the Fuel Solenoid. See PMD - Pump Mounted Driver

FS or FSOL (Fuel Solenoid) - The PCM-controlled injection pump solenoid valve that opens and closes to provide hi-pressure fuel to each cylinder.

Fuel Shut Off Solenoid - How to "gut" the Fuel Shut Off Solenoid Here


Gauges - Gives information about what the engine is doing so you can monitor boost, EGTs, and transmission temperatures.
Gasoline - A fuel that is never to be used in your diesel engine. Do not add gasoline in your diesel tank!

Glow Plugs - A small pencil-shaped heater, must be needed to start the 6.5L engine. For more information click here.
  • GM TSB on 9G Glow Plugs - Replaced By 11G Glow Plugs in 1996 Click Here
  • GM TSB on 11G Glow Plugs - Replaced in 2000 By "BERU" Glow Plugs Click Here
  • Glow Plug Cycle Time Chart - Based on Temperature and Battery Voltage Click Here
  • Glow Plug Over Ride Modification Look Here
  • Another way to get more glow duration time Convince the PCM that it's -40* out. See how here or here.
  • Swelled Glow Plug Removal: Click Here.
  • Not so common failure of glow plugs Click Here.

Glow Plug System Troubleshooting Tips
  • How to "Read" Glow Plugs: Click Here
  • Glow Plug Relay Connector Voltage: Click Here
  • No Wait To Start Light/Glow Plug Relay Not Working: Click Here
  • Wait To Start Light Comes On While Driving: Click Here
  • OBDI Trouble Shooting Guide Here

GMTDScan Basic - GMTDScanTech - See Scan Tool

Grounds - Proper grounds are very important!
  • Engine Grounds: A complete write up with pics Click Here.
  • Engine Grounds - Another write up with pics in a .pdf file Click Here
  • Alternator Mounting Points: Critical for alternator performance Click Here

Hard Starting - Several reasons given. Search for GLOW PLUGS, Optical sensor, optic sensor, PMD, OPS, lift pump. There are a variety of reasons given for difficulty in starting. Read this thread.

Harmonic Balancer - Rubber-isolated cast-iron ring and hub assembly mounted on the crankshaft nose that is prone to failure. The balancer fails as the rubber deteriorates, and it contributes to crank breakage/failure. See this thread for more information.
  • How To Install Here
  • Removal/Install Tools Here and Here
  • Tool For Stopping Engine Rotation While Removing/Installing Harmonic Balancer Click Here

Heads/Headgasket Issues - to understand better what's happening inside the engine and pin down where the problem maybe, GMCTD explains better the failures here in this post.

Head Lights - There are a few mods you can do to make your head lights work better when driving at night.
  • For one way to do the "All On Headlight Mod" See Here

Heater Hose Tee - Suburban heater hose Tee fitting - DIY fix Here

High Idle Modification - a straightforward and inexpensive Mod you can do yourself to raise the idle rpm of your truck. Comes in 2 easy-to-follow flavours, complete with pictures:
HO Water Pump - '98-up 130gph pump, part of the required coolant upgrades, HO is cast into the upper housing
  • For information about the HO Water Pump Click Here
  • Also refer to Engine Cooling 6.5 Cooling System Upgrade Parts
Attached Files
File Type: pdf GM TSB 1996 Diesel Engines - Glow Plugs.pdf (80.1 KB, 532 views)
File Type: pdf GM TSB 2000 Diesel Engines - Glow Plugs.pdf (58.8 KB, 490 views)
File Type: pdf Hydroboost Install.pdf (307.9 KB, 481 views)
File Type: pdf LCG_NoStart03.pdf (774.5 KB, 670 views)

Last edited by OkDually; 06-10-2018 at 10:24 PM. Reason: Add Hydroboost rebuild