95 6.5 TD new injectors - now low mpg

[Steak&Eggs]

HI: I got this K3500 in 95 new, with a 12 T lift bed and a grain body. It was a work truck in Haines Alaska most of its life, lite duty really. Firewood and hauling a Ditch Witch R65 burying CATV cable in Haines and Skagway.
The pump module failed and was replaced with a Heath Diesel unit - no more trouble with that. The IP (about 50K miles) had a moment after leaving Whitehorse in Canada going back to Haines (60 below) it was winter. So I turned around and went back to Whitehorse, left it at a dealer and rented a car to get on to Haines. They had switched to new diesel fuel with lower lubrication that did not suit the original IP, I have had no issues with the replacement about 130K miles on the truck now. Its now a farm truck in Missouri. The injectors were showing some signs of wear - some smoke at start up and needed a plug in below 30 degrees to start without a lot of cranking... Still getting 13 MPG loaded with 3.5 T crushed gravel. But I thought I would fix the injectors and get back to 16 MPG empty. It weighs about 8900 empty and 13000 loaded. So I ordered online new pintle and seat and installed them in the original body with all the original parts. Started it up with the intake off to check for leaks (and I found one!) started first crank and ran very well. seemed as strong as ever. Put it all together and it seemed fine. did not see any start up smoke. But I noticed the fuel gauge going down awfully fast, so I checked and got 10 MPG. The new injector seat had the same part # stamped as the original. I had tested each one before install and the pattern and chatter seemed to be good. So I took it to a shop and had them replace my rebuilds with new GM injectors, the engine ran fine pulled like it always did (I had added a chip +100 ft lb torque +65 HP) But still getting 10 MPG. Not to happy about that....
So spent a lot of time online and found Bosch injectors like the originals, I ordered those and took the new GM ones back and got a rebate (that was enough to pay for the Bosch replacements) It ran fine and pulled like it always did but I still get 10 MPG. Now that I have been using it that way for about a year I notice it will puff a small amount of grey thin smoke at startup - does not seem to smoke after that loaded or not. I did notice that when warm it is harder to start, usually (when cold) the second crank it would be running but when up to operating temp it will crank over 5 or 7 times and then start. When the original injectors were good in the summer I did not need glow plugs to start cold. And just yesterday I was moving a load of scrap metal down a shaded gravel road going about 15 MPH using the engine braking going down hill when I gave it fuel to go up the other side I noticed the engine was not running (never did that since I moved driver module Many years ago) It started normal for itself being hot and no issues for the rest of the trip.
I did get a GMTD scan tool program and took some snapshots of the system. Perhaps if someone is familiar with fuel reading they would know if they are normal or not (I sure do not know). I post one below for grins!

On cruise going up hill, not sure if boost pressure is accurate, I replaced the vacuum motor with a spring.....

Snapshot created 7/16/2025 4:13:43 PM
__________________________________________________________________
ENGINE SENSORS
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Engine run time: 00:20:54
Boost pressure (MAP): 24.46 PSI
Desired EGR: 15.23 PSI
Desired idle: 638 RPM
EGR pressure: 14.36 PSI
EGR duty cycle: 0 %
Engine coolant temp: 203.3 F°
Engine speed: 2662 RPM
Glow plug relay feedback: 0.1 Volts
Glow plug voltage: 0.1 Volts
Ignition voltage: 13 Volts
Wastegate duty cycle: 55.9 %

__________________________________________________________________
INFORMATION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
PCM Calibration ID: 4735
Current DTCs: 0
Accel. ped. pos. 1: 0.73 Volts
Accel. ped. pos. 2: 4.33 Volts
Accel. ped. pos. 3: 4 Volts
Barometric pressure (BARO): 13.5 PSI
Battery voltage: 12.9 Volts
Fuel temperature: 142.3 F°
Intake air temp: 240.1 F°
Throttle position: 0 %
Turbo boost (Calculated): 10.95 PSI
Voltage reference sensor: 1.3 Volts

__________________________________________________________________
INJECTION PUMP SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Actual injection pump timing: 36.52 Deg °
Cam reference missed: 0 Counts
Crank reference missed: 0 Counts
Fuel calibration: 135 Counts
Fuel rate: 67.81 mm³
Fuel rate - Cruise: 67.5 mm³
Fuel rate - Idle: 0 mm³
Fuel rate - Maximum transient: 79.69 mm³
Fuel rate - Throttle requested: 0 mm³
Injection pulse width: 1.71 ms
Injection timing - Measured: 14.4 Deg °
Injection timing - Desired: 14.3 Deg °
TDC offset: -1.67 Deg °

__________________________________________________________________
TRANSMISSION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
3-2 PWM solenoid duty cycle: 0 %
Cruise target speed: 57 MPH
Cruise speed error: 2 MPH
Current gear of transmission: 3 Gear
Current torque signal pressure: 90 PSI
Current transmission ratio: 1:0.06 Ratio
Error between desired and actual shift times for latest 1-2 upshift: 0.08 Sec
Error between desired and actual shift times for latest 2-3 upshift: 0.05 Sec
Force motor (PCS) - Duty cycle: 3.9 %
Force motor (PCS) - Feedback current: 0.02 Amps
Force motor (PCS) - Reference current: 0 Amps
Time of latest 1-2 upshift: 0.35 Sec
Time of latest 2-3 upshift: 0.22 Sec
TCC PWM solenoid duty cycle: 6.2 %
TCC slippage: 2 RPM
Transmission input speed: 2665 RPM
Transmission output speed: 2664 RPM
Transmission temperature: 186.8 F°
Turbine speed: 2665 RPM
Vehicle speed: 55 MPH

__________________________________________________________________
STATUS FLAGS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Shift lever:
Drive 4

Cruise control:
Disengage condition
Cruise standby mode

TCC mode word 1:
TCC is being forced off
TCC enable solenoid valid
Low threshold for COPETCC selected
Use hyst. for vehicle speed
TCC is in release mode, slipping
TCC is in locked-adjust mode
TCC is being applied
Negative slip recently prevents apply

TCC mode word 2:
TCC PWM is on
Perform release
Perform apply
Min. threshold occurred
TCC Bus. is valid
NDT occurs
Delay is in progress
Min. throttle occured

IOD port A:
Glow plug relay - Closed/Open
Stepper motor inhibit - Run/Inhibit
Service Throttle Lamp - On/Off
EGR vent enable - On/Off
Shift A - On/Off
Shift B - On/Off
TCC enable - On/Off (4L60E only)
Force Motor enable - On/Off

IOD SOD status register:
Coolant temp. pullup select - On/Off
Trans. temp. pullup select - On/Off
Fuel calibration temp. select - On/Off
Check Engine Lamp - On/Off
PWM1 - Reset/Normal
PWM2 - Reset/Normal
PWM3 - Reset/Normal
PWM4 - Reset/Normal

System status word:
FM shut off due to low battery
Force Motor pulse in progress
Power is On/Off
COP2 is being serviced
Delco instrumentation PROM
Powertrain is in motion

Discrete flags:
Brake - On/Off
A/C Compressor - Engaged/Disengaged
Power enrichment - Active/Inactive
Kickdown pattern - Active/Inactive
Four-Wheel Drive Low - Active/Inactive
Cruise low - Active/Inactive
Diagnostic - Requested/Not requested

Well that is the story If anyone has any ideas or questions Just Shoot!
Thanks, Larry

 

[dbrannon79]

the only thing I see that stands out is your IAT at 240 degrees. this means the engine is sucking in hot air from the engine compartment rather than outside air.

did you have the injectors tested and balanced before installing? if so, what pressure were they set to? another question is did you test the old set that was still giving you decent MPG's. every rig is different and favors one pressure over the other. general set pressure is 1950psi, but some engine like less, some like more.

it's hard to say what things caused your mileage to drop, there are lots of variables that can contribute to that. different blends of diesel, wind direction, idle time, other loads on the engine like the alternator, AC and whatnot. the biggest would be the fuel condition and additives it has and if you add your own on top of that. I myself have experienced lower mileage with most all of the additives I have tried. gets even worse during the cooler months if you run anti-gel additives.

 

[dbrannon79]

Also from looking at the trans data, your driving 55 mph and your in 3rd not 4th (overdrive) and TCC is not engaged. 2600 RPM at 55 mph will suck some fuel!

 

[Big T]

Engine Coolant Temp at 203+ is on the warm side.

Boost pressure of 24+ psi is extremely high.

 

[ak diesel driver]

24 is including atmospheric so 9ish

 

[dbrannon79]

you have to subtract the boost pressure (map) from the barometric pressure (baro) to get the actual boost pressure on these rigs. he's only running 10.95 PSI from the turbo.

 

[Steak&Eggs]

the only thing I see that stands out is your IAT at 240 degrees. this means the engine is sucking in hot air from the engine compartment rather than outside air.

did you have the injectors tested and balanced before installing? if so, what pressure were they set to? another question is did you test the old set that was still giving you decent MPG's. every rig is different and favors one pressure over the other. general set pressure is 1950psi, but some engine like less, some like more.

it's hard to say what things caused your mileage to drop, there are lots of variables that can contribute to that. different blends of diesel, wind direction, idle time, other loads on the engine like the alternator, AC and whatnot. the biggest would be the fuel condition and additives it has and if you add your own on top of that. I myself have experienced lower mileage with most all of the additives I have tried. gets even worse during the cooler months if you run anti-gel additives.

IAT at 240 degrees
I think it was a hot sunshiny day going up hill, it had dropped out of 4th to climb the hill...
did you have the injectors tested and balanced before installing?
When I replaced the pintle and valve body every thing else was reused. There were no shims to set the pressure, I do not remember what the pressure was but they were all close together and the pressure was as described online.... I did test the old set, I seem to remember spray patterns that were not great, a little ragged and no chatter. I think one of the pressure readings was quite a way off from the rest.

I only note nothing was changed except the injectors when the trouble started. Its strange to me some of the old injectors were peeing a little stream sometimes - none of the rebuilt or new ones I put in had that (or any) problems I could see, and I got better MPG with the original worn out injectors. Of course I never had occasion to look at such things until this engine injectors got some wear on them...
I think I saved video of the tests, I'm not sure I tested the Bosch injectors that are installed now. I will have to look and see what I have - all I need is some time to go back and look at the videos... I can do that if it will help.

Thanks

 

[Steak&Eggs]

Engine Coolant Temp at 203+ is on the warm side.

Boost pressure of 24+ psi is extremely high.

I had a load on, it was a hot day climbing a hill. It had dropped out of 4th for that. I have a boost gauge - the most I have seen is a very quick peak of 14 psi usually tops out around 12 -13 psi. It always had enough power to do what I needed so I did not worry about that. I am not sure what the computer thinks about the boost (if it has a sensor for that or calculates it) the vacuum pump and motor are removed and replaced with a spring. I realize that might not be as efficient but it is totally reliable. I had issues with the vacuum system and have had none with the spring.
Thanks for the reply

 

[Steak&Eggs]

Also from looking at the trans data, your driving 55 mph and your in 3rd not 4th (overdrive) and TCC is not engaged. 2600 RPM at 55 mph will suck some fuel!

I have this snapshot of the same trip running in 4th maybe on level roadway or at least not up a steep grade in overdrive.

Snapshot created 7/16/2025 4:10:03 PM
__________________________________________________________________
ENGINE SENSORS
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Engine run time: 00:17:14
Boost pressure (MAP): 19.92 PSI
Desired EGR: 15.23 PSI
Desired idle: 806 RPM
EGR pressure: 14.29 PSI
EGR duty cycle: 0 %
Engine coolant temp: 211.4 F°
Engine speed: 2062 RPM
Glow plug relay feedback: 0.1 Volts
Glow plug voltage: 0.1 Volts
Ignition voltage: 12.9 Volts
Wastegate duty cycle: 69.9 %

__________________________________________________________________
INFORMATION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
PCM Calibration ID: 4735
Current DTCs: 0
Accel. ped. pos. 1: 0.73 Volts
Accel. ped. pos. 2: 4.33 Volts
Accel. ped. pos. 3: 4 Volts
Barometric pressure (BARO): 13.4 PSI
Battery voltage: 13 Volts
Fuel temperature: 134.2 F°
Intake air temp: 240.1 F°
Throttle position: 0 %
Turbo boost (Calculated): 6.52 PSI
Voltage reference sensor: 1.3 Volts

__________________________________________________________________
INJECTION PUMP SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Actual injection pump timing: 33.44 Deg °
Cam reference missed: 0 Counts
Crank reference missed: 0 Counts
Fuel calibration: 135 Counts
Fuel rate: 43.44 mm³
Fuel rate - Cruise: 43.44 mm³
Fuel rate - Idle: 0 mm³
Fuel rate - Maximum transient: 79.69 mm³
Fuel rate - Throttle requested: 0 mm³
Injection pulse width: 1.72 ms
Injection timing - Measured: 11.6 Deg °
Injection timing - Desired: 11.8 Deg °
TDC offset: -1.67 Deg °

__________________________________________________________________
TRANSMISSION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
3-2 PWM solenoid duty cycle: 0 %
Cruise target speed: 57 MPH
Cruise speed error: 127.5 MPH
Current gear of transmission: 4 Gear
Current torque signal pressure: 71 PSI
Current transmission ratio: 1:0.75 Ratio
Error between desired and actual shift times for latest 1-2 upshift: 0.08 Sec
Error between desired and actual shift times for latest 2-3 upshift: 0.05 Sec
Force motor (PCS) - Duty cycle: 25 %
Force motor (PCS) - Feedback current: 0.41 Amps
Force motor (PCS) - Reference current: 0.39 Amps
Time of latest 1-2 upshift: 0.35 Sec
Time of latest 2-3 upshift: 0.22 Sec
TCC PWM solenoid duty cycle: 6.2 %
TCC slippage: 2 RPM
Transmission input speed: 2773 RPM
Transmission output speed: 2769 RPM
Transmission temperature: 186.8 F°
Turbine speed: 2080 RPM
Vehicle speed: 57 MPH

__________________________________________________________________
STATUS FLAGS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Shift lever:
Drive 4

Cruise control:
Disengage condition
Cruise standby mode

TCC mode word 1:
TCC is being forced off
TCC enable solenoid valid
Low threshold for COPETCC selected
Use hyst. for vehicle speed
TCC is in release mode, slipping
TCC is in locked-adjust mode
TCC is being applied
Negative slip recently prevents apply

TCC mode word 2:
TCC PWM is on
Perform release
Perform apply
Min. threshold occurred
TCC Bus. is valid
NDT occurs
Delay is in progress
Min. throttle occured

IOD port A:
Glow plug relay - Closed/Open
Stepper motor inhibit - Run/Inhibit
Service Throttle Lamp - On/Off
EGR vent enable - On/Off
Shift A - On/Off
Shift B - On/Off
TCC enable - On/Off (4L60E only)
Force Motor enable - On/Off

IOD SOD status register:
Coolant temp. pullup select - On/Off
Trans. temp. pullup select - On/Off
Fuel calibration temp. select - On/Off
Check Engine Lamp - On/Off
PWM1 - Reset/Normal
PWM2 - Reset/Normal
PWM3 - Reset/Normal
PWM4 - Reset/Normal

System status word:
FM shut off due to low battery
Force Motor pulse in progress
Power is On/Off
COP2 is being serviced
Delco instrumentation PROM
Powertrain is in motion

Discrete flags:
Brake - On/Off
A/C Compressor - Engaged/Disengaged
Power enrichment - Active/Inactive
Kickdown pattern - Active/Inactive
Four-Wheel Drive Low - Active/Inactive
Cruise low - Active/Inactive
Diagnostic - Requested/Not requested


__________________________________________________________________
No ideas on the cruise speed error, it is reported as the same speed in 2 places so it must be a glitch ??
Cruise target speed: 57 MPH
Vehicle speed: 57 MPH

Thanks, Larry

 

[dbrannon79]

Running a spring on the waste gate might cause teh PCM not to be happy. but in your snapshot there were no codes set. the Turbo Master which is a bracket and spring setup might help you set the boost pressures under load and help keep the boost down low when cruising

with the old injectors having a lower (worn out) pop pressure the timing would have been allowing it to fire ever so slightly early allowing a cleaner burn. just a theroy here, but higher pop pressures causing a slightly later firing with the timing might be part of the cause of lower MPG's as the PCM sees it and pushes more fuel.

most injectors straight from the suppliers won't have any shims, and as we have found out are not pressure tested before being sent out to sellers.

I rebuilt a set for my 93 and of course it also has a badly worn out engine with perfuse blow by, but I did loose some MPG's after installing them, but as bad as you did though.

 

[dbrannon79]

I have this snapshot of the same trip running in 4th maybe on level roadway or at least not up a steep grade in overdrive.

Snapshot created 7/16/2025 4:10:03 PM
__________________________________________________________________
ENGINE SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Engine run time: 00:17:14
Boost pressure (MAP): 19.92 PSI
Desired EGR: 15.23 PSI
Desired idle: 806 RPM
EGR pressure: 14.29 PSI
EGR duty cycle: 0 %
Engine coolant temp: 211.4 F°
Engine speed: 2062 RPM
Glow plug relay feedback: 0.1 Volts
Glow plug voltage: 0.1 Volts
Ignition voltage: 12.9 Volts
Wastegate duty cycle: 69.9 %

__________________________________________________________________
INFORMATION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
PCM Calibration ID: 4735
Current DTCs: 0
Accel. ped. pos. 1: 0.73 Volts
Accel. ped. pos. 2: 4.33 Volts
Accel. ped. pos. 3: 4 Volts
Barometric pressure (BARO): 13.4 PSI
Battery voltage: 13 Volts
Fuel temperature: 134.2 F°
Intake air temp: 240.1 F°
Throttle position: 0 %
Turbo boost (Calculated): 6.52 PSI
Voltage reference sensor: 1.3 Volts

__________________________________________________________________
INJECTION PUMP SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Actual injection pump timing: 33.44 Deg °
Cam reference missed: 0 Counts
Crank reference missed: 0 Counts
Fuel calibration: 135 Counts
Fuel rate: 43.44 mm³
Fuel rate - Cruise: 43.44 mm³
Fuel rate - Idle: 0 mm³
Fuel rate - Maximum transient: 79.69 mm³
Fuel rate - Throttle requested: 0 mm³
Injection pulse width: 1.72 ms
Injection timing - Measured: 11.6 Deg °
Injection timing - Desired: 11.8 Deg °
TDC offset: -1.67 Deg °

__________________________________________________________________
TRANSMISSION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
3-2 PWM solenoid duty cycle: 0 %
Cruise target speed: 57 MPH
Cruise speed error: 127.5 MPH
Current gear of transmission: 4 Gear
Current torque signal pressure: 71 PSI
Current transmission ratio: 1:0.75 Ratio
Error between desired and actual shift times for latest 1-2 upshift: 0.08 Sec
Error between desired and actual shift times for latest 2-3 upshift: 0.05 Sec
Force motor (PCS) - Duty cycle: 25 %
Force motor (PCS) - Feedback current: 0.41 Amps
Force motor (PCS) - Reference current: 0.39 Amps
Time of latest 1-2 upshift: 0.35 Sec
Time of latest 2-3 upshift: 0.22 Sec
TCC PWM solenoid duty cycle: 6.2 %
TCC slippage: 2 RPM
Transmission input speed: 2773 RPM
Transmission output speed: 2769 RPM
Transmission temperature: 186.8 F°
Turbine speed: 2080 RPM
Vehicle speed: 57 MPH

__________________________________________________________________
STATUS FLAGS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Shift lever:
Drive 4

Cruise control:
Disengage condition
Cruise standby mode

TCC mode word 1:
TCC is being forced off
TCC enable solenoid valid
Low threshold for COPETCC selected
Use hyst. for vehicle speed
TCC is in release mode, slipping
TCC is in locked-adjust mode
TCC is being applied
Negative slip recently prevents apply

TCC mode word 2:
TCC PWM is on
Perform release
Perform apply
Min. threshold occurred
TCC Bus. is valid
NDT occurs
Delay is in progress
Min. throttle occured

IOD port A:
Glow plug relay - Closed/Open
Stepper motor inhibit - Run/Inhibit
Service Throttle Lamp - On/Off
EGR vent enable - On/Off
Shift A - On/Off
Shift B - On/Off
TCC enable - On/Off (4L60E only)
Force Motor enable - On/Off

IOD SOD status register:
Coolant temp. pullup select - On/Off
Trans. temp. pullup select - On/Off
Fuel calibration temp. select - On/Off
Check Engine Lamp - On/Off
PWM1 - Reset/Normal
PWM2 - Reset/Normal
PWM3 - Reset/Normal
PWM4 - Reset/Normal

System status word:
FM shut off due to low battery
Force Motor pulse in progress
Power is On/Off
COP2 is being serviced
Delco instrumentation PROM
Powertrain is in motion

Discrete flags:
Brake - On/Off
A/C Compressor - Engaged/Disengaged
Power enrichment - Active/Inactive
Kickdown pattern - Active/Inactive
Four-Wheel Drive Low - Active/Inactive
Cruise low - Active/Inactive
Diagnostic - Requested/Not requested


__________________________________________________________________
No ideas on the cruise speed error, it is reported as the same speed in 2 places so it must be a glitch ??
Cruise target speed: 57 MPH
Vehicle speed: 57 MPH

Thanks, Larry

look at your engine coolant temp, 211 is in dangerous territory for these engines!

also 2700~ rpm at 57 mph is where your MPG's are going! what is your rear axle gear ratio and what size are your tires? I assume you are running a 4L80E trans.

 

[dbrannon79]

@Will can tell you all about engine temps on these rigs! you want it to stay under 200. your risking cooking cylinder #8 piston and rings.

There is a pipe plug in the head near the #8 cylinder, pull that plug out and install you a mechanical temp gauge there to keep in the cab. run a 180 temp thermostat, and make sure your fan clutch is working as it should.

pull the upper section of the fan shroud and grille out of the way and use a air compressor blow gun to clean out the stack real good. radiator fins, condenser, engine oil and trans oil coolers. If you have never blown them out before, wear a mask, your neighbors will think your truck is on fire with all the dust and debris getting blown out!!

 

[Big T]

I have this snapshot of the same trip running in 4th maybe on level roadway or at least not up a steep grade in overdrive.

Snapshot created 7/16/2025 4:10:03 PM
__________________________________________________________________
ENGINE SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Engine run time: 00:17:14
Boost pressure (MAP): 19.92 PSI
Desired EGR: 15.23 PSI
Desired idle: 806 RPM
EGR pressure: 14.29 PSI
EGR duty cycle: 0 %
Engine coolant temp: 211.4 F°
Engine speed: 2062 RPM
Glow plug relay feedback: 0.1 Volts
Glow plug voltage: 0.1 Volts
Ignition voltage: 12.9 Volts
Wastegate duty cycle: 69.9 %

__________________________________________________________________
INFORMATION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
PCM Calibration ID: 4735
Current DTCs: 0
Accel. ped. pos. 1: 0.73 Volts
Accel. ped. pos. 2: 4.33 Volts
Accel. ped. pos. 3: 4 Volts
Barometric pressure (BARO): 13.4 PSI
Battery voltage: 13 Volts
Fuel temperature: 134.2 F°
Intake air temp: 240.1 F°
Throttle position: 0 %
Turbo boost (Calculated): 6.52 PSI
Voltage reference sensor: 1.3 Volts

__________________________________________________________________
INJECTION PUMP SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Actual injection pump timing: 33.44 Deg °
Cam reference missed: 0 Counts
Crank reference missed: 0 Counts
Fuel calibration: 135 Counts
Fuel rate: 43.44 mm³
Fuel rate - Cruise: 43.44 mm³
Fuel rate - Idle: 0 mm³
Fuel rate - Maximum transient: 79.69 mm³
Fuel rate - Throttle requested: 0 mm³
Injection pulse width: 1.72 ms
Injection timing - Measured: 11.6 Deg °
Injection timing - Desired: 11.8 Deg °
TDC offset: -1.67 Deg °

__________________________________________________________________
TRANSMISSION SENSORS
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3-2 PWM solenoid duty cycle: 0 %
Cruise target speed: 57 MPH
Cruise speed error: 127.5 MPH
Current gear of transmission: 4 Gear
Current torque signal pressure: 71 PSI
Current transmission ratio: 1:0.75 Ratio
Error between desired and actual shift times for latest 1-2 upshift: 0.08 Sec
Error between desired and actual shift times for latest 2-3 upshift: 0.05 Sec
Force motor (PCS) - Duty cycle: 25 %
Force motor (PCS) - Feedback current: 0.41 Amps
Force motor (PCS) - Reference current: 0.39 Amps
Time of latest 1-2 upshift: 0.35 Sec
Time of latest 2-3 upshift: 0.22 Sec
TCC PWM solenoid duty cycle: 6.2 %
TCC slippage: 2 RPM
Transmission input speed: 2773 RPM
Transmission output speed: 2769 RPM
Transmission temperature: 186.8 F°
Turbine speed: 2080 RPM
Vehicle speed: 57 MPH

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STATUS FLAGS
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Shift lever:
Drive 4

Cruise control:
Disengage condition
Cruise standby mode

TCC mode word 1:
TCC is being forced off
TCC enable solenoid valid
Low threshold for COPETCC selected
Use hyst. for vehicle speed
TCC is in release mode, slipping
TCC is in locked-adjust mode
TCC is being applied
Negative slip recently prevents apply

TCC mode word 2:
TCC PWM is on
Perform release
Perform apply
Min. threshold occurred
TCC Bus. is valid
NDT occurs
Delay is in progress
Min. throttle occured

IOD port A:
Glow plug relay - Closed/Open
Stepper motor inhibit - Run/Inhibit
Service Throttle Lamp - On/Off
EGR vent enable - On/Off
Shift A - On/Off
Shift B - On/Off
TCC enable - On/Off (4L60E only)
Force Motor enable - On/Off

IOD SOD status register:
Coolant temp. pullup select - On/Off
Trans. temp. pullup select - On/Off
Fuel calibration temp. select - On/Off
Check Engine Lamp - On/Off
PWM1 - Reset/Normal
PWM2 - Reset/Normal
PWM3 - Reset/Normal
PWM4 - Reset/Normal

System status word:
FM shut off due to low battery
Force Motor pulse in progress
Power is On/Off
COP2 is being serviced
Delco instrumentation PROM
Powertrain is in motion

Discrete flags:
Brake - On/Off
A/C Compressor - Engaged/Disengaged
Power enrichment - Active/Inactive
Kickdown pattern - Active/Inactive
Four-Wheel Drive Low - Active/Inactive
Cruise low - Active/Inactive
Diagnostic - Requested/Not requested


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No ideas on the cruise speed error, it is reported as the same speed in 2 places so it must be a glitch ??
Cruise target speed: 57 MPH
Vehicle speed: 57 MPH

Thanks, Larry

Engine Coolant says 211+. If you’d going to tow, you need to replace that GM turbo with something larger.

If you had a load on, then your mpg will be way lower. 10 mpg is not unheard of depending on the size of the load.

 

[Steak&Eggs]

look at your engine coolant temp, 211 is in dangerous territory for these engines!

also 2700~ rpm at 57 mph is where your MPG's are going! what is your rear axle gear ratio and what size are your tires? I assume you are running a 4L80E trans.

Hmmm, 2060 rpm @ 57 mph not climbing much grade on the second snapshot. It still has the automatic tranny it came with, same rear end ratio.. Do not know what it is, but it and everything else is the same. The only change is the injectors? Tires are LT 235/85 R16 10ply same ones that got 13 with 3.5 T gravel on it. 16 when empty before the injectors got worn out... The snapshots probably only had 1500 lbs it was scrap metal mostly empty space... Boost pressure on level roadway is usually around 0 psi it only gets higher when pulling harder. I guess I could have put the originals back in but after doing it 3 times I didn't want to, I already know how they work! It just looks to me like the new injectors are not up to spec one way or another. The first parts replaced were made in china - so I should not be surprised... I do not know where the Delco injectors installed by the shop were made, but they had the same issue. The Bosch injectors are not made in Germany, they come from India. It just seems like the correct spec part is not available?

So if I am stuck with what I have maybe water injection or Hydrogen injection will help. Or both? I never had any issue that left me beside the road, just a lot of ready to go driving mostly... its been a reliable rig. Always did my own work, except the injectors by the shop - I ended up removing them and returning.. I'm not a mechanic I only know what I have been forced to learn to keep it running. As with all my equipment.

Larry

 

[Steak&Eggs]

@Will can tell you all about engine temps on these rigs! you want it to stay under 200. your risking cooking cylinder #8 piston and rings.

There is a pipe plug in the head near the #8 cylinder, pull that plug out and install you a mechanical temp gauge there to keep in the cab. run a 180 temp thermostat, and make sure your fan clutch is working as it should.

pull the upper section of the fan shroud and grille out of the way and use a air compressor blow gun to clean out the stack real good. radiator fins, condenser, engine oil and trans oil coolers. If you have never blown them out before, wear a mask, your neighbors will think your truck is on fire with all the dust and debris getting blown out!!

When the headlight plastic lens got cloudy I replaced them with '89 sealed beam headlights so I would not have to mess with them again. In the process with the front end grill & stuff off I blew out all the radiators and painted any rusty areas (the power stearing radiator) since then have put about 4K miles on the truck. I only use it to haul gravel and firewood on the place. Occasional trips to haul scrap or crushed rock gravel for the driveway.

Larry

 

[dbrannon79]

Maybe I mis-read something, I was looking at your trans input and output speed. next time your out n about, pay attention to your tach and speed and see what they look like. your most likely have 4:10 gears for hauling. my 95 has 3:73 gears, 265-75-16 tires and I get about 2200ish at 70mhp and my 93 has 4:10 gears and 245-75-16 tires with a gear vendors overdrive unit, gets 2000ish at 70mph. on my 95 I used to have 4:10 gears and would get around 2400 rpm at 70mph same tires.

I do know the faster you go over 60-65 or 55 loaded, fuel mileage goes out the window on these rigs! I pulled my 30' camper out to the coast here in Texas with my 95 and going about 50-60 mph, my mileage went to about 9-10 mpg where I normally get around 13-14 empty depending on how much lead is in my foot LOL

If all else looks and performs good, I would suspect fuel quality. every winter here my fuel mileage drops due to the additives they use in the pipelines, summer time mileage goes back up. Not sure when or how much additives are used in fuel up in your neck of the woods, but it's something to look at. service stations around here mostly use "unbranded" fuels, the diesel comes out murky yellowish in color unless you get fuel from a shell station, that fuel is a clear as water and supposedly cleaner too.

for fuel grades, I used to run an old kerosene heater in my garage for the winter. got tired to the one station in our town that keeps it in bulk not having any on hand so I ran an experiment burning diesel in it... well I found out the diesel from the shell stations that comes out clear burns perfectly fine in it and the "unbranded" dingy yellow diesel would clog up the wick in just by filling it once and trying to burn it!

My 95 truck is also very picky when it comes to extra lube additives. everything I have tried here at the local stores always drops my mileage! I have since been using Stanadyne lubricity formula (one with the blue label) only requires 4 ounces per fill-up and it hasn't really effected mileage. supposedly it's one of the best to use for lubrication on the IP.

 

[Steak&Eggs]

Yes, I travel with the cruise set at 60 on the speedo, RPM is about 2200 at that speed. MPG seems to be the same loaded or not... The mileage went to heck as soon as the new injectors were put in. Same fuel in the tank, (it is clear - I checked at the fuel filter). Have never had any issue with fuel around here - I live on a farm out in the woods. I get my fuel in one of the towns I travel to depending on what I am after.... Moved back to the family farm in '05. We have several diesel powered things and no issues with any of those! My 94 Dodge with the Cummins 5.9 gets 25 MPG using the georgia overdrive - and staying below 60 mph. its rpm at 60 is 1750.

Larry

 

[dbrannon79]

Well, I would say go ahead and pull the injectors, mark each for which cylinder they came from. test them, pull them apart, inspect, clean, and retest.

I use a ultrasonic cleaner I got off the jungle site to clean them. use some water base solvent like ZEP 505 cleaner. if you need shims I found that you can get some off the jungle site that fit and seem to work well.

Here is the link for the shims I found that will work.

Amazon.com

Thanks to @MrMarty51, I have a pop tester and some shims here if you don't have a pop tester, if you like, mail them injectors off to me and I will test, clean, and set the pressures for you. No charge, just the shipping cost. another option is if you have a local diesel shop nearby that will do it for you. I'm still learning or as they say teaching myself while enrolled in youtube school LOL to do this kinda thing, so I'm no professional at it! There are other members here who are pros at it too.

 

[Steak&Eggs]

Well, Thank You for the generous offer! I will post some links to the readings I got before install. I am reaching a conclusion (! HA) the injectors somehow must be the issue, since 3 different sets acted essentially the same way - and the old worn out set got better mpg. Although it will start on its own now down to about 0 degrees F, with the worn originals at 30 degrees I had to plug it in. Originally it would start down to about - 20 with no 110 VAC power. Though there were no shims in the original injectors they must have met spec that these replacements do not meet.

There is a large Perkins diesel shop near Springfield MO - about 2.5 hours drive from here. I will give them a call and see of they have a machine that can put the injector under actual operating conditions and set to spec. And if they are willing to work on a lowly pickup.... I will take the injectors out and take them in if they are willing. Perhaps that will help, if it does not - then I guess I'm stuck!

http://lglackin.com/1995GMCk3500TD/Bosch/One256.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Two257.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Three258.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Four259.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Five260.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Six261.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Seven262.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/Eight263.mp4

http://lglackin.com/1995GMCk3500TD/Bosch/FirstRun.mp4

I do not know why I did not give a hard yank on the handle to see if chatter happened or not, I think I did but not on the video (and they did chatter). Sorry for the crummy video I do not know how to hold the camera steady .

Larry

 

[dbrannon79]

engine sounds good, but in your tests I would question the spray pattern of #3 and #7. #4 and #8 is what you want to hear and see from all of them especially from new injectors.

I have always thought about rigging up an old DB2 IP, doesn't matter if it's off a 4 banger tractor or from a truck, but setting it up with one line having a gauge tee'd inline and run it off a drill so you can get as close to as possible to real operating conditions. it's hard to do with a hand pump tester.

All you'd need to set one up is a single line for one injector, the others can be fed with rubber hose back into the fuel supply that's going into the IP. An electric motor with RPM control would be optimum driving the IP.