GM 6.5 FAQ & Information Sticky ░▒▓▌»New Members Read!«▐▓▒░

[knkreb]

Here is a compiled listing of the most popular topics discussed here at DieselPlace.com under the 6.5L section. This is to help you speedily find your answers, without having to wait for a reply to your question. We love to answer questions, and enjoy gathering around the computer to help others out. We’ve all been there. This forum is a living library of information.

Click on the solid underlined word of any topic of interest and it will hyperlink you to the area in the forum where the information was first posted, for example if you click on the underlined word OBDI - Codes this will take you to the thread with information about the OBDI codes.


If you don’t find a topic listed, feel free to do a search. You may have to do an individual word or a phrase search, as with any search engine you may need to be creative in describing what you are looking for, don't give up if first search you type comes back with nothing found, there is a entire forum search, & search within a forum sub group, author, subject, date. may be worth your while to read all FAQ topics 1st so you can inject common to GM 6.2 & 6.5 phrases to work with on your searches.

Best way to use this thread:
Hit Control + F and a box should come up. Type in a main word (ex. PMD) and hit enter or next. This will search the thread and highlight every time the word PMD comes up. Or, you can just browse around the thread and find what you need. Everything is in alphabetical order.

We also have a Diagnostic Checklist. This is intended to help you get all questions together before posting. We’ll end up asking questions, then you’ll have to post back, etc, etc. It takes awhile. The Diagnostic checklist is a self-help resource. Use it and you may have it fixed yourself. If not, post your findings and we’ll jump right on it.


Thanks and enjoy!
The Diesel Place Staff
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Here are some Good Threads to Check Out!

6.5L Diagnostic Check List: Here

6.2/6.5L DIY Sticky Thread: Here

What I did to my 6.5L Today Thread: Here

6.5L Member Dyno Runs: Here

6.5L Official MPG Thread: Here

6.5L Member Locator: Here

6.5L Official Chat Room Night: Tuesdays at 9:00PM EST, more information Here.

FAQ: Purchasing 6.5L Diesel: Here

[Green Machine]

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18:1 compression Engine
Techinical Discussion on the 18:1 Engine

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A1 Customs - A vendor to be very careful of. Aka, steaksauce.

• Check out here: Click, Click ,Click, Click

Antilock Braking System (ABS) - Electronically controlled system that senses wheel lockup during braking and relieves hydraulic pressure at wheel which is about to skid.

Acetone - Do not use in your tank!! It easily evaporates at 70deg.

Acronyms- Find out meanings to common acronyms.

Additive(s) - Anything added to crankcase or fuel tank to enhance and preserve operation of the engine system.

Air Intakes - see Boost and Filters

Air Conditioning - To understand this system Click Here.

Alternator - Device that generates voltage which provides power to charge batteries and other electrical devices within the vehicle electrical system.

• Common problems of a bad alternator - Low voltage, batteries not charging, erratic tachometer readings.

Alternative Fuel - Any fuel that is not Diesel. SVO, WVO, Bio-Diesel

APP (Accelerator Position Potentiometer) - This acts as a throttle cable through the drive-by-wire system. Commonly known as an APPS (Accelerator Pedal Position Sensor).

• How to tell when it's bad. Click Here

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Battery connections - Various problems associated with these. Read this thread, can cause voltage issues, intermittent stalling, studdering, etc.

Battery Terminals - The stock side terminal connections are weak. You can make your battery connections MUCH more stable by doing a simple mod if you want to keep your side terminals.

• Check this Mod out Click Here and another version Here.

Blower Motor - A device located on the bottom right of dash that blows air into the cab. For a testing procedure on this Click Here.

Boost Diagnostics - For information regarding this topic see this thread.

Boost Fooler - By using a 10k Pot you can fool the PCM by adjusting what it reads from the MAP Sensor. For more information about this mod Click Here.

Brakes - Device used to slow or stop a vehicle.

• Front pads and rotor replacement example Here.
• Full floating 14 bolt rear end Here

Buying a 6.5L Diesel - Please see Purchasing a 6.5L Diesel.

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CDR (Crankcase Depression Regulator) - Similar to a PCV valve on a gas engine. It regulates the amount of vacuum in the engine crankcase to prevent oil leaks. Click here for technical info.

CEL (Check Engine Light) - see MIL

CODES - There are the two styles of computer "codes" that you will be looking for, Pre 1996 (OBD I) and 1996+ (OBD II).

• Understanding Codes
• OBD-I codes
• OBD-II codes
• DTC Lookup tool

Computer - see PCM

Coolant system - see engine cooling

Cooling modification - upgrade to a 1997+ cooling system (High output water pump and dual thermostat) with this info. See also engine cooling

CPS (Crankshaft Position Sensor) - PCM reads the CPS module to indicate TDC for each piston, necessary to determine precise timing for the injection pulse.

Cruise control - sometimes fails with a DTC (engine code/service engine light). Can also not work due to a bad PMD.

• You can add cruise control to your "non-cruise" truck too, Find out here!

CTS - See ECT

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Dash (Bezel) Removal - To remove the Dash Bezel (the piece that goes around steering wheel radio, ac controls, etc) Click Here. That link will also show how to remove the gauge cluster.

Door Repairs - Find out how to complete some door repairs yourself by clicking here.

DTC (Diagnostic Trouble Codes) - see Codes or use the DTC lookup tool

Dyno Runs - Click Here to see members dyno runs.

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ECM (Engine Control Module) - The primary computer which controls the Insight's internal combustion engine. In the 6.5 Diesel we use a PCM, see PCM.

ECT (Engine Coolant Temperature) - Sensor is mounted in the t-stat crossover manifold, gives PCM accurate temperature input for determination of advance and fuel rates. The Resistance changes at different temperatures with this sensor. Here is a chart or resistance values.

• ECT 'Fooling' for better cold starts:
  Great mod for Command-Start systems! Look here
• For a modified version, Look here

EGR (Exhaust Gas Recirculation) - An emission device that recirculates exhaust gases from the engine back into the intake and combustion chambers. This lowers combustion temperatures and reduces NOx.

• EGR Valves can be found on vin "S" trucks (1500, 2500LD trucks, 6 lug hubs).
• If you would like to remove the EGR system from your truck you must either block off EGR ports in intake or get a vin "F" intake and install. Then you must get computer reprogrammed to erase the EGR system from computer (Heath Diesel or Kennedy Diesel reflashes), or you may receive codes and trigger the CEL.
• For EGR Removal Look Here

EGT - Exhaust Gas Temperature

Electricity - Understanding how to interpret your meter when working on the lift pump and OPS Click here.

Engine cooling - see here or See Here or these indexed posts on overheating How it affects the engine. The higher the temperature leaving the engine, the greater the chance for damage to the engine. Reading the temperature pre- or post-turbo can vary several hundred degrees. Read article for more information.

• Helpful info: Here, Here, Here.

E-PROM or EEPROM - A blue type chip found inside of the ECM on 94/95 6.5L Trucks.

Extended crank time - see hard starting. May be associated with an optical sensor failure on the IP, but not all hard starting is IP related. Cold weather, with a lot of grey/whitish smoke on start up maybe glow plug related. See Glow Plugs for more information. Read up also on fuel supply issues: Lift pump, OPS, fuel line leaks, etc.

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Fan Clutch - This is a fluid clutch that controls the engine fan. it reduces fan noise and increases fuel economy. To modify the clutch to engage at lower temps Check Here
Feed the Beast - This is a modification to your filter manager. It will increase the fuel flow though the filter manager.

• To find out more information, Click here and Click here.

Filter Manager - 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.

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.

Fuel cap - Can cause excessive vacuum in fuel tank. Excessive vacuum in a Diesel fuel tank is not desirable. For full information Read this thread.

Fuel contamination - 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.

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 Filtration - Filtering Diesel fuel is very important. Fuel can be dirty and the injection pump must need clean fuel to last.

• To see an auxiliary fuel filter setup Click 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 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. This is a common problem, for more info Read this thread. Do all diagnostics first before only replacing. there is no way to test other then replace.

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

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Gauges - Gives information about what the engine is doing so you can monitor boost, EGTs, and transmission temperatures.

• Pre-Turbo Probe Installation: Click Here
• Boost Gauge Installation: Click Here.
• To light up your gauges Click Here

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.

• 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.

Grounds, Engine - Proper grounds are very important! A complete write up with pics is can be found here and here.

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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.

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

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:

• OBD-I
• OBD-II

HO waterpump - '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

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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. See this thread for troubleshooting details. For details on removing the key tumbler, see this thread.

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.

• For operation information See 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.

Injectors - Injects diesel fuel into the combustion chambers.

• Injector Part Numbers: Cilck Here.
• Myth about Marine Injectors revealed: Click Here.
• Guide to replacing injectors: coming soon.

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
• Finally, here's a Front-mount DIY install: here

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Leaks, fuel - Fuel tank and lines as reported by some mid 90's owner's

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. Check out OPS as well before condemning the lift pump. Read this thread.
> See also electricity for thread on troubleshooting practices

• To view a video on how to jump the Lift Pump on a 92-94 6.5L Click 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.

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MIL (Malfunction Indicator Light) - Also known as Service Engine Soon, Check Engine Light.

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.

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!

Main Bearing Girdle How To Make A 5 Main Girdle Click Here
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[Joeairforce]

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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 Lubrication Specialist kit.

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 Relay Mod: Check 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.

• 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.

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Part Index - listing of parts and part number see this thread

PCM (Powertrain Control Module) - The computer behind your glove box - monitors and controls all aspects of 6.5 electronic fuel injection and 4L80E transmission shifting.

• For information about PCM codes see codes.

Pictures of things - Photo thread.

PMD - Pump mounted driver - aka FSD, Known trouble spot in the 6.5 electronic fuel injection system. For more information See this thread.

PMD Extension Harness - This is necessary if you want to remote mount your PMD out of the engine bay. Making your own is easy if you are careful. But whether to crimp or solder, that's an ongoing question.

• Making a PMD\FSD Extension Harness - to Crimp or Solder?
• PMD\FSD harness wiring
• PMD Harness Connectors

Power - We all probably want more power. There are a few options to improve power in your truck. If you don't see anything in this thread try a search, there are many things people have done to their trucks.

• improving power - see here
• Power Ratings - click here

Purchasing a 6.5 Diesel - Things to consider and How to purchase one.

• 6.5L Buying Checklist: Here.

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Recall Information - There are many recalls out there, here are some info on them:

• Power steering shaft recall info Click Here.

RPO codes - options that came with your vehicle. See glove box for sticker. These are three digit codes like: G80, L65, L56, etc. Click here for a common listing of options and their meanings.

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Scan Tool - Tech2 is the GM Scan tool. It is very expensive to purchase though. There are other available software for the PC completely that emulates Tech2 functionality at a very reasonable price. For information about these programs see below -

• '94-'95 OBD1 will need the GMTDScan Tech PC software and cable from ENGH Motors.
• '96-'06 OBD2 will need the Car Code or AutoEnginuity PC software and cable, available on the net, both service GM.
• Both are very user-friendly, does everything the TECH2 does for engine and transmission test and control and plugs into your USB port on laptop/computer.

SES - see MIL

Sheared cam key - For more information about this Click here.

Snorkel - Is the plastic intake inside of the passenger side fender, for more info Click Here.

Speedometer Calibration - Click Here for a mod to calibrate your speedometer if you are running a different gear ratio or larger sized tires.

Stalling - Common problem with the DS4 electronic injection pump system. Do a search for PMD's, lift pumps, OPS, etc. This problem may be electrical or in the fuel supply system. Thread to check out. To properly diagnose your stalling, use diagnostic checklist to pin point cause, no need to replace expensive parts that may not fix the problem.

Stanadyne Specs for IPs - Listing of Stanadyne Specs found here.

Steaksauce - see A1, search "Steaksauce" to find info on this scammer.

Steering Stabalizer - Installation steps with pictures Here.

Stumbling - momentary loss of power, Check out this thread, Sometimes called fishbiting.

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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.

TDC Offset (Top Dead Center Offset) - This is a factor the computer uses to compute timing for fuel injection.

• For technical information about TDC Offset Click here.
• For informationa bout setting timing on an OBD I link coming soon.
• For information about setting timing on an OBD II Click Here.

Theft Deterrent Learn - Here is the procedure for an OBD-II.

Towing - Many people tow with the 6.5. It may have its limits, but it makes for a decent truck.

• A story of pulling a FEMA trailer Click here.
• Towing ratings Click here.

Torque Specs - Common engine torque specifications Click Here.

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.

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. Examples here or here
• 1996-2000: vertical. Examples here or here

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

Vacuum 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. For in depth information, see this thread.

• For Vacuum Pump removal information Look Here.

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.

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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.

Wastegate - The "flapper" valve that opens to bypass exhaust gasses around the turbine, thus reducing Boost to specified and safe level for engine operation.

• Turbo operation: See this thread.
• For more information: See this thread.

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.

Windshield Wiper Delay Fix - GM wipers have a documented cold-solder problem on their circuit boards, often causing the wipers to stop working. Here's a pictorial step-by-step guide on how to replace the board, or you can try to fix the problem with a little solder See here

WMI - Water mist injection an alternative to using an intercooler. See here for more informatin

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