The symptoms are constant. When I first fire it up it rocks like crazy and hangs out around 1000rpms sometimes jump from 1100-900 . But if I put it in any other gear it will idle and purr like a kitten so flawless. The throttle is very touchy and when getting at your cruising speed it will not stay at a constant speed or rpm. The lifter pump is on a toggle and works great. Bought a new pdm and nothing changes. It's already in the bumper relocation kit. I'm lost on this one . 6.5s are very confusing with there fuel systems. Things I just wanna throw in there my water temp sensor is not plugged in. I can't find the harness.( Any one got a picture? ) fuel gauge says it's full. ( I dropped tank to actually find out it was full but figured it was working so put it back and latter that week it said full still so guess it was a win ,lose situation.) I'm leaning to a bad ip or throttle position sensor? Any one please I need advise thank you all and have a blessed day.

 

Links to GM 6.5L Turbo Diesel Training Manuals
Download (save) both of those to your PC for quick reference...

Unless your the only person driving the vehicle, I suggest you restore the Fuel Pump Relay Circuit to stock configuration. Add the LPR mod if you like.. Toggle switch is to easy to forget to turn ON or OFF..
Note that there isnt a throttle Position Switch on EFI 6.5TDs. They have APP and they are often misdiagnosed too..

Perform the following..
OBD System Check and Fuel Pump Relay Circuit Diagnosis
See DS4 Manual, page 99 "Reading Diagnostic Trouble Codes (DTC) at the MIL" (Malfunction Indicator Lamp) aka Service Engine Soon [SES] lamp and "Clearing Diagnostic Trouble Codes At The DLC (Data Link Connector)"
Note: '94 models, the DLC's Fuel Pump Test Terminal is "G", not "F" as it is with '95 OBD1 models..

Fuel Contamination Inspection and Cleaning and Fuel Specific Gravity Check

Fuel Supply System Checks
Be sure to perform ALL of the Fuel Supply System Checks in order and in there entirety.. BE AGONIZINGLY THOROUGH,, 95% of the EFI 6.5TD complaints stem from some failure in the low pressure fuel delivery system.
Air leaks, fuel restrictions, and faulty grounds are the MOST LIKELY SUSPECTS, unfortunitely those most "Important Preliminary Checks" are routinely skipped, assumed good, and/or done half ***. That is until the new IP failed to fix s'it. If all your doing is going through the motions, dont bother. Might as well take it to the shop and prepare for the boat ride as in "Bust Out Another Thousand" and hope your not on Gilligans Island.

DO NOT ASSUME because there are no obvious fuel leaks that the fuel system is air tight and/or restriction free.. If it were only that easy.

Air is the EFI 6.5TD Kryptonite.
Grungy Grounds, its Nemesis...

As clever as that may sound, it sums it up quite nicely.


Get busy, report back anything not working properly or not as described BEFORE you start replacing a damn thing. Dont go chasing PCM Ghost as so many often do, replacing critical sensors simply because there may be a DTC. Doing so may easily COMPOUND the problem so its imparitive that you follow prescribed instructions (DO NOT SKIP STEPS), again be thorough..

DTCs may not necessarily indicate the part(s) are bad, but rather that a fault occurred within the system. Its up to the tech to "translate" what the vehicle is saying through its symptoms and/or DTCs, unfortunitely very few techs speak EFI 6.5TD fluently, many are dumbfounded and create excuses and mythical creatures to cover there *** while taking your cash.
So, wheres your PMD located <sarcasm....

FYI. Its common to find spooky DTC(s) following a routine fuel filter change, anything that opens the fuel supply system to air intrusion so you shouldnt get overly concerned with DTCs until youve eliminated all other possible suspects, remote as they may be..

Taken straight from the DS4 training manual...

"Underneath its electronics, the 6.5L EFI diesel engine is a basic V8 diesel powerplant. The fuel pump, lines, and injectors still deliver fuel according to the basic rules of hydraulics. Electronics simply make them operate more precisely. Your understanding of the 6.5L mechanical systems and how they relate to each other is still indispensable for troubleshooting and repairing faults.

With the 6.5L EFI, a basic understanding of electronics is also necessary. Being able to read wiring schematics will allow you to identify components, wire colors, pin numbers, and wire routing when electrical diagnosis is required. The diagnostic trouble trees contained in Sections 3 and 10 of the Driveability and Emissions (Diesel) Service Manual are based on the schematics and require at least elementary knowledge of electrical theory."



Yet 20 plus years after the fact, it continues to routinely kick everyone cash, DIYrs and professionals alike.. Go figure.





Good Luck

 

Thanks for the reply I will jump on it Sunday or Saturday due to my work schedule I have small amount of free time. I will eventually get it . The truck sat for 7 years and I replaced the transmission. It was basically a bolt restoration and tracking down parts my dad gave away. Do you know Where all the grounds are cause I only see one on the manifold?

 

1 other thing since your running fly by wire and that is that thing your foot drags water mud snow grime and other stuff on. The throttle peddle itself. It is electronic as well and reving up and down symtoms are often blamed on the pump when its the sensors in the throttle peddle. Sometimes you can get lucky and spray it with a can of electronics cleaner work the peddle while the truck is off spray some more and then let dry and start truck and see if that cures it. I dont care how well they sealed it after 20 years junk gets in there.

 

Thanks for the reply! Yesterday I managed to get a little somewhere on the blazer. I redid 4 of the grounds. And I read some Where if I unplug the camshaft position sensor and it idles normal then I should replace . Well it did idle normal so Monday is when it gets here. But could this also be my problem why it don't stay at a constant rpm? Can sensor malfunction telling the computer something else and miss firing??

 

Both Sensors can malfunction and cause the issue you are having. An what HeavyChevy said could apply as well. Finding electrical issues is kinda like playing clue. You need a good manual and lots of time and patients in tracking the issue down.

 

Well in the process of removing the old cam shaft sensor the clip broke so now the sensor is stuck in the bore hole.. just my luck. So now this Sunday I'll have to remove the oil pan and get it out and out new one in and see how she runs again. Will post when did. Thanks all for help.

 

That sucks man. I know your pain on things snapped off and dropped in, things stuck etc. All the bearings in 3 turbos I am trying to rebuild are locked in one was so damn heat bound togeather from bearing failure that I basically ruined any chance of rebuilding it trying to get every thing out.