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
View Single Post
Old 03-15-2014, 03:55 AM   #5 (permalink)
R.I.P. Sam
Diaric's Avatar
Join Date: Jan 2008
Location: Bentley , Alberta
Posts: 32,091




IAT (Intake Air Temperature) - Sensor, mounted in the upper intake plenum, PCM monitors IAT to determine fuel rates and safe levels of Boost

Information, Literature - For some information about literature on the 6.5L diesel Click here.

Ignition Switch - Point of failure that can create stalling. This is NOT THE KEY MECHANISM, but a multiple-circuit switch with relay-type contacts that powers all the components during the "run" state. Upon failure, you will lose dash board and engine will stall - it mimics turning key off. Most folks instantly think that the PMD is at fault, but from time to time, this is actually the cause.

For trouble shooting Ignition Switches:
1994 & 1995 See this thread for details.
1996+ See this thread for details.

For details on removing the key tumbler, see this post with a PDF of the process..

Injection Pump (IP) - The fuel delivery device that pumps high pressure fuel for injection into the cylinder at the precise time for a combustion event in the cylinder. Your pump will vary depending upon model year. 1993 and earlier is a mechanical DB2 pump. 1994 and thereafter is a DS4 electronically-controlled injection system.
  • DS4 IP Component Diagram Here
  • How A Mechanical IP Works Here
  • How To Install A Larger IP Inlet On A DB2 IP Click Here
  • For operation information See Here.
  • Injection Pump/Injector Line Diagram Here
  • DS4 Key Components Picture Click Here
  • DS pump info for lower lubricity fuels See Attachment Here.
  • The injection pump has a 11 year 120,000 mile Extended warranty, for more information Click Here.
  • To turn fuel up on a DB2 pump Click Here For a video of how to do it Click Here
  • Reference thread on different methods to turn pump up Click Here
  • How to Replace Injection Pump? Click Here to see how with Pictures! For another thread about this Click Here and Click Here.
  • Dead Injection Pump, Diagnosing the Pump and CableClick Here.
  • Injection Pump Closure Time Information - DS4: Click Here
  • IP Turning Tool Click Here
  • DTC35 & DTC 36 - If you are getting both codes, here is a diagnostic tip Click Here
  • DS4 IP Diagnostics Click Here

Injection Pump Service Bulletins
  • GM Service Bulletin - Code DTC 35/DTC P1216 Click Here
  • 6.5 Stanadyne Diagnose Service Bulletin Click Here

Stanadyne Parts Bulletins
Stanadyne IP Application - 6.2L & 6.5L Engines
Injectors Injects diesel fuel into the combustion chambers.
Intake modifications - snorkel mod

Intercooling - Cooling (Boost) charge-air See also WMI or water mist injection
  • Here's a How-To install of a Spearco Intercooler by Turbine Doc
  • Here's a DIY WTA intercooler install: here
  • Here's a DIY hanging ATA intercooler install: here
  • Here's a Step-by-step DIY hanging ATA install: here and here
  • Here's a Top-Mounted DIY ATA install: here and here
  • DIY Water Mist Injection system using mostly off the shelf parts: Click Here
  • Finally, here's a Front-mount DIY install: here




KOKO Procedure - See TDC Offset


Leaks, fuel - Fuel tank and lines as reported by some mid 90's owner's
  • Using Air Pressure To Find Fuel System Leaks: Click Here.
Lift Pump - Small electrical fuel pump that is located on the frame rail under the drivers seat. Noticeable "purring" noise when engine is off. Known trouble spot. This can cause lack of power, hard starting, stalling, etc.

Lift Pump Facts (from GM Service Manual):
  1. The 1988-1993 Model Year lift pump should deliver fuel with a minimum volume of 0.24 liter (1/2 pint) in 15 seconds at a pressure of 40 to 60 kPa (5.8 to 8.7 psi).
  2. The 1994+ Model Year lift pump should deliver fuel with a minimum volume of at least 0.24 liter (1/2 pint) in 15 seconds and pressure of 3 psi minimum with the engine cranking, the ESO disconnected, and the fuel line open after the filter to an approved canister
  3. When the pump is at rest, a spring pushes the hollow plunger in the direction of the outlet. Both the inlet and outlet valves are closed, keeping fuel in the supply line from draining back to the fuel tank.
Lift Pump Trouble Shooting
  • Lift Pump Test & OPS Diagnostics Click Here. See Electricity for troubleshooting practices
  • Pictures showing how to jump the Lift Pump on a 1992-94 6.5L Here
  • Pictures showing how to jump the Lift Pump on a 1995 6.5L Here and Here
  • How to jump the lift pump on a 1996-1999 6.5L (Pending)
  • 1996+ Lift Pump Prime Connector - Apply 12v to this connector to run the lift pump: Here
  • Reference for operating the lift pump with auto tranny in D and key in crank position Here
Lights, LED - Add LED to your gauge cluster for a custom look, Check This Thread for information.

Limp Mode - A Backup Mode of allowing the engine to run, yet not at full power. Usually due to a "missing piece to the puzzle" that the ECM needs to compute timing, fuel delivery, etc.

Locker - Adding a locker? Look at this thread.

Locking up TCC modification to OBD-I trucks. See this thread.

Low Coolant Warning Sensor Location By Model Year See Engine Cooling


Main Bearing Girdle How To Make A 5 Main Girdle Click Here

Manifold Bolt Sizes- Click Here

Manifold Bolt and Heat Shield Part #'s- Click Here

Mass Air Flow Sensor (MAF)-OBDII Trucks
  • Pictures from L56 Here
  • Does your truck have a MAF? Here
MIL (Malfunction Indicator Light) - Also known as Service Engine Soon, Check Engine Light.
  • 1991-1993 With Automatic Transmission - Constant or Intermittent MIL ON, No DTC's Set TSB Click Here

Mirrors - There are different types of mirrors that can be added to our trucks with little to no modification.
  • If you would like to add newer style Chevy mirrors on your pickup Click Here or Or Here.
  • Dodge style mirrors on your truck Click Here.
Missing (Misfire) - Engine briefly "misses" a combustion event. Thread to check out Search for fuel delivery, lift pump, OPS, and PMD.

Modifications (DIY) - Check out this thread for DIY Modifications to your 6.5L Engine and Truck Related Parts!

Motor Mount Inserts Poly Inserts Click Here

Multi Function Switch How to replace the multi function switch in a 1995 to 1998 Click Here


NV4500 See Transmission - NV4500



OBD (On-Board Diagnostic) - Where PCM monitors all systems, reporting failures with universal numeric codes specific to each system across all OEM vehicle marques.
  • For code explanations see Codes.
Oil - Maintaining your oil is very important in an engine. Make sure you change at the correct intervals and replace with the correct oil. For more information Click here.

Oil Cooler Lines - Stock oil cooler lines are known to leak and cause failures. When an oil cooler line fails, it will lose all the oil and cause an engine failure. Make sure you keep an eye on your stock lines, if they are leaking you are at risk for seizing up your engine.
  • A great alternative to stock lines would be purchasing and installing the Leroy Diesel kit.
  • How To Replace Oil Cooler Lines, With Pictures Click Here

Oil Filters
  • Diagnosing Engine Oil Filters With Collapsed Center Tubes Click Here

Oil Pressure Switch (OPS) - OPS Known trouble spot for not allowing the lift pump to operate. Read this thread. This is also the sensor for the oil pressure gauge in the gauge cluster on dash. When the OPS craps out, your lift pump may not run and the IP can be starved for fuel, leading to stalling, erratic behaviour under load, loss of power, etc.
  • OPS' Role in 1996+ Truck: From Racer55 "For OBDII primary power for the LP is as shown in the diagram, the ECM activates the prime cycle through the relay and once it sees a running engine from OS/CPS signals activates the relay for constant run operation. Should the relay circuit fail, the OPS is backup LP power-it also operates the LP after engine shutdown while oil pressure bleeds off." From glagulator "The lift pump on your 96 gets power from the LP relay and the OPS when the engine is running. PCM control of the LP is independent of OPS function. LP will function normally even if OPS is not. A parallel/redundant circuit. Either source can fail and the other will take over when running. Power for both feeds and the PCM is from the ECM-B fuse, any problem with that and it will not run." Wiring Diagram Here
  • OPS Does Your 1994 - 1995 Truck Need The Relay Mod: Check Here
  • OPS Does Your 1992/93 Truck Need The Relay Mod:Check Here
  • OPS Relay Mod: Check Here.
  • OPS Relay Mod Wiring Diagram: Here.
  • OPS Relay Mod Wiring Diagram - Diesel and WVO: Here

Optical Sensor - The device on the top of the injection pump that provides a high and low resolution frequency signal to the PCM to determine fuel injection timing.
  • How The Optical Sensor Works: Click Here
  • Replacing the Optical Sensor - How To Click Here
  • For 'Optical Sensor Bump' please Look Here for more information.
Optical Sensor Filter Harness - A small device plugs in between the optical sensor and the vehicle wiring harness. The device can cause drive-ability issues if it is not making proper connection. A Picture of the filter harness.

Overheating - See cooling modifications or here.
Attached Files
File Type: pdf IP Key Components.pdf (103.2 KB, 607 views)
File Type: pdf 226.pdf (475.3 KB, 535 views)
File Type: pdf 119.pdf (110.6 KB, 668 views)
File Type: pdf gm-6.5-EFI-diagnostic.pdf (568.4 KB, 563 views)
1987 6.2l Jimmy , being restored,4" lift, 35 mudders 1993 W350 5.9 , custom stretched cab, duelly flatdeck
2001 VW TDI Jetta 4 door loaded 2001 VW TDI Golf 2 door swapped engine project
Originally Posted by 4320diesel View Post
well to make your pump retarded, you could let it hang out with me for a day
Originally Posted by Hawkstrong View Post
Diaric wins thread derailment......
Originally Posted by High Sierra 2500 View Post
Yeah Diaric, I gotta say, I'm afraid I'm going to have to give you an official warning on that.
6.2 FAQ's AND ANSWERS Click Here
My Restoration Thread Click Here
Alberta Coal Roller Member #2

Last edited by OkDually; 09-15-2019 at 01:22 PM. Reason: removed Lubrication specialists link ( NSV)