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.
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.