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Discussion Starter · #1 ·
I have a 95 Z71 K1500 S VIN 6.5 Turbo. I got the truck as a basket case. It had new PMD, OPS, Lift Pump, Starter, Batteries, new filters and oil. I got it started after about 2 hours of cursing the day I towed it home. It ran rough and had a bunch of codes (OBD1). It was running not great, but I kept adding the exhaust parts in hopes that the turbo boost would help. The crossover seemed to help some, but adding the downpipe choked the truck on the clogged catalytic converter (cat). I drilled 2 holes in the front of the cat casing (1/4 or 3/8"). I was careful to not drill the catalyst material itself, but close enough I could heat it. The holes were at about 7 and 5 O'clock. I took a MAPP gas click torch and used it to light the soot on the front of the cat. Once it started glowing I started the truck and revved the engine a bit to keep it going (lit). It burnt all the carbon out in about 10 minutes. Keep a fire extinguisher handy (mine blew sparks out the drill holes). Once the cat was cleared it ran just ok and I was able to put self tapping screws in the drill holes (engine off). Then I used a bunch of information from threads here to clear my DTCs and reset using KOKO (key on, key off) method. Truck now runs like a dream.

DO NOT START with jumper installed ( plug and unplug jumper with key off only)

DTC reset, key off, jumper the last 2 pins on the upper row (they have metal visible, #5 &6 counting from the left). I used a paperclip as the jumper. checked my codes and reset them by pressing both brake and accelerator to the floor. Verified codes were reset (turn off and then back to on to get only code 12 - no problems).

TURN KEY OFF AND UNPLUG JUMPER BEFORE STARTING

Fuel system learn mode:
engine above 170 DEG F (I pre-warmed mine prior to DTC reset)
Clear all DTC's (process above)
Turn Ignition On with engine OFF (get a timer or a clock with seconds)
Hold Down Throttle for minimum 45 Secs
Turn OFF Ignition for a minimum 30 Secs
Start engine, when temp gets above 170 DEG F (helps to preheat) and RPM below 1500 (just idle in Park) a new TDCO will be learnt. You can tell TDCO is relearning as the timing figures will momentarily drop and the engine will momentarily lug. (Mine surged a bit and settled down).

The DTC reset and learn mode worked the first time for me, I preheated the truck, cleared the codes, then learn mode. Learning happened almost immediately on the warm engine and was very obvious. The whole reset and learn took ~ 20 minutes and I went from a non-drivable truck to a great one. If you get new DTC codes while warming up, the learn mode doesn't happen, so try warming up before resetting.

Truck had a new lift pump but a sealed gas cap (not a diesel cap). That is why the last lift pump failed. I replaced it immediately.

Clogged cat is fine now, no new codes. Spot welded the holes closed. Blow-by is way down and dropping with more driving. New PCV was $50.

This is my first post and I wish that I could have found all of this great information in one place. Thank you to all who posted before me, this site is invaluable. I hope that by putting all of this in one place, I can help the next person.

The excessive backpressure from the cat had the same symptoms of the injection timing being way off (only real difference was very little flow at the tailpipe). No power, rough running, lugging under load, tons of smoke, feels like lack of boost, unburned fuel in exhaust. In my case I had both to start, and still had most of the same symptoms after clearing the cat. Unless you don't have any exhaust at the tailpipe, try the learn mode before you blame the emissions controls. If you have a truck that has been sitting with no batteries, it may run badly if the Injection Pump timing is not set perfectly and you may want to manually start the the learn mode.
 

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Discussion Starter · #2 ·
OBD-I is pre 96 vintage truck coding use OBD-II for trucks of 96 & later years

The Data Link connector is located below the steering wheel lower left rim of the dash just about knee cap height.

Rectangle Slope Font Parallel Pattern

1. Use a jumper (paperclip, etc) to connect terminals A & B. The connection/removal of the jumper between terminals (A&B) should be done with the ignition switch OFF. Also to prevent potential volt spike to PCM remove clip with Key OFF once jumper is installed then turn key to on/run (not full start) to begin the flashing sequence

The Service Engine Soon light will flash Code 12 three times to indicate that the diagnostics are working. Trouble codes will then follow, one at a time, three times each. DTC 12 will only appear if there are no other codes.


2. The codes appear in numerical order, and each code repeats itself three times before the next begins. This is different from some other ECM's.


3. It is helpful to the diagnostic process to know when codes are setting, particularly if there is more than one. Hence, clearing the codes is something you may wish to do. Clearing the codes may be accomplished by simultaneously depressing the brake and accelerator pedals fully while the PCM is in diagnostic mode (terminals A and B connected). It will not appear that you have cleared the codes until the next time you power up in diagnostic mode, however.


DTC 12 - No Codes Present
DTC 13 - Engine Shutoff Solenoid Circuit Fault
DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit Low (High Temp)
DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temp)
DTC 16 - Vehicle Speed Sensor Buffer Fault
DTC 17 - High Resolution Circuit Fault
DTC 18 - Pump Cam Reference Pulse Error
DTC 19 - Crankshaft Position Reference Error
DTC 21 - Accelerator Pedal Position 1 Circuit High
DTC 22 - Accelerator Pedal Position 1 Circuit Low
DTC 23 - Accelerator Pedal Position 1 Circuit Range Fault
DTC 24 - Vehicle Speed Sensor Circuit Low (Output Speed Signal)
DTC 25 - Accelerator Pedal Position 2 Circuit High
DTC 26 - Accelerator Pedal Position 2 Circuit Low
DTC 27 - Accelerator Pedal Position 2 Circuit Range Fault
DTC 28 - Transmission Range Pressure Switch Circuit
DTC 29 - Glow Plug Relay Fault
DTC 31 - EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum)
DTC 32 - EGR Circuit Error
DTC 33 - EGR Control Pressure/Baro Sensor Circuit High
DTC 34 - Injection Timing Stepper Motor Fault
DTC 35 - Injection Pulse Width Error (Time Short)
DTC 36 - Injection Pulse Width Error (Time Long)
DTC 37 - TCC Brake Switch Stuck "ON"
DTC 38 - TCC Brake Switch Stuck "OFF"
DTC 39 - TCC Stuck "OFF"
DTC 41 - Brake Switch Circuit Fault
DTC 42 - Fuel Temperature Circuit Low (High Temp)
DTC 43 - Fuel Temperature Circuit High (Low Temp)
DTC 44 - EGR Pulse Width Error
DTC 45 - EGR Vent Error
DTC 46 - Malfunction Indicator Lamp (MIL) Circuit Fault
DTC 47 - Intake Air Temperature Sensor Circuit Low (High Temp )
DTC 48 - Intake Air Temperature Sensor Circuit High (Low Temp )
DTC 49 - Service Throttle Soon Lamp Circuit Fault
DTC 51 - PROM Error
DTC 52 - System Voltage High Long
DTC 53 - System Voltage High
DTC 54 - PCM fuel circuit error
DTC 56 - Injection Pump Calibration Resistor Error
DTC 57 - PCM 5 Volt Shorted
DTC 58 - Transmission Fluid Temp Circuit Low
DTC 59 - Transmission Fluid Temp Circuit High
DTC 61 - Turbo Boost Sensor Circuit High
DTC 62 - Turbo Boost Sensor Circuit Low
DTC 63 - Accelerator Pedal Position 3 Circuit High
DTC 64 - Accelerator Pedal Position 3 Circuit Low
DTC 65 - Accelerator Pedal Position 3 Circuit Range Fault
DTC 66 - 3-2 Shift Control Solenoid
DTC 67 - TCC Solenoid Circuit (Open or Short)
DTC 68 - Transmission Component Slipping
DTC 69 - TCC Stuck "ON"
DTC 71 - Set/Coast Switch Fault (Cruise Control)
DTC 72 - Vehicle Speed Sensor Circuit Loss (Output Speed Signal)
DTC 73 - Pressure Control Solenoid Circuit (Current Error)
DTC 74 - Transmission Input Speed (TIS) Sensor Circuit
DTC 75 - System Voltage Low
DTC 76 - Resume/Accel Switch Fault (Cruise Control)
DTC 78 - Turbo Wastegate Solenoid Fault
DTC 78 -Turbo Wastegate Solenoid Fault
DTC 79 - Transmission Fluid Over Temperature
DTC 81 - Transmission 2-3 Shift Solenoid Circuit
DTC 82 - Transmission 1-2 Shift Solenoid Circuit
DTC 83 - Torque Converter Clutch
DTC 84 - Accelerator Pedal Position Circuit Fault
DTC 85 - Transmission Gear
DTC 86 - Transmission Gear Ratio Error
DTC 87 - Transmission Gear Ratio Error
DTC 88 - Top Dead Center Offset Problem
DTC 91 thru 98 - Cylinder Balance
DTC 99 - Accelerator Pedal Position Sensor 5-Volt Reference Problem


KOKO Routine as follows:

engine above 170 DEG F

Clear all DTC's

Turn Ignition On with engine OFF

Hold Down Throttle for minimum 45 Secs

Turn OFF Ignition for a minimum 30 Secs

Start engine when temp gets above 170 DEG F and RPM below 1500 a new TDCO will be learnt. You can tell TDCO is relearning as the timing figures will momentarily drop and the engine will momentarily lug.
 

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Welcome to DieselPlace
(y)
 

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Glad you got your truck running. Good work.
If you need more info like the good things you posted. There is a sticky in the top of all the 6.5 threads titled Info: - The 6.5L FAQ's... The Master List of...
There is a wealth of info contained there that may help you keep your 6.5 running great. Plus complete free shop manuals for every year to DL.
Welcome.
 
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Welcome.
KOKO routine does not work on a 1995 OBD1.
Must be 1996-up OBD2.
 
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