haroldwca
Newbie
I was stumped for a while on this. My truck is a 1988 K1500 SBSC with the 5.7/700R4. I pulled the transmission to replace the rear main seal in the engine. While re-installing the transmission, I connected the 4-pin connector on the driver's side that controls the lock-up torque converter (TCC) solenoid. It had not been connected since I bought the truck over a year ago. It had been shifting as well as I expected except for the lack of lock-up in 4th gear.
While doing a shakedown lap of the neighborhood, everything seemed normal, and then less than 1/4 mile from the house it simply quit. It seemed like an electrical failure, abrupt and instant, rather than sputtering to a halt like fuel starvation. A friend pulled me home, and I set about doing diagnostics. Just because it was rather simple, I used a 9V battery to fire the injectors while cranking the engine. It ran briefly. (I didn't try it for long.) Among other things, I checked the fuel pump - it worked when power was applied to pin G of the ALDL connector. Next I performed a visual check of the distributor, which was old. As bad as it looked, it may have been original to the Titanic. I replaced it reasoning that, due to its condition, it was time for replacement even without hard confirmation of a failure. No change.
One thing that seemed odd is that I didn't get a SES light at any time. Not when the engine died. Not when I was diagnosing (engine off, key on). Not at all. I even removed my instrument cluster and switched bulbs with a light that I knew was previously working. Still no SES light. This absence made me suspect that my ECM had failed. A used one with the same PN at the local pick and pull was cheap enough, and I swapped units, thinking that if it did solve the problem I would order a new one for the long haul, and have an extra "known good" ECM around for test purposes. No change.
While searching again online for ideas, I realized that I had missed step one. If it seems electrical, check the fuses. The first one I pulled was the ECM - bad. I replaced the bad fuse and drove out around the block several times. No problems. However, the next morning on my way to work it died again just like before less than 1/4 mile from the house. I caught a ride to work.
After work, I went back to the truck and examined the ECM fuse. It was bad. I pulled the fuse from a non-essential circuit of the same rating, fired it up, and drove home slowly. I replaced the fuse from the circuit I scavenged and let it run in the driveway for a while. No faults. I decided to attempt to make it fail again and observe anything I could about conditions or circumstances of the failure. I drove around the block five times with no fault or failure. Then I drove out of the neighborhood. In exactly the same location as the first time, it died again. This time (a) I had a pocket full of extra fuses, and (b) I realized that it was blowing the fuse just after the transmission shifted into 4th gear, and was ready to lock up the torque converter. I remembered the unplugged TCC circuit from before the repair. Since the lockup is activated only in 4th, I replaced the fuse, then drove the same route with the selector in 3rd. No fault or failure. I drove the route four more times without any incident. Finally, I dropped it back into 4th. Same fault, same location. I drove home, unplugged the connector, and have been driving a week without issue. Incidentally, with the connector unplugged, the SES light illuminates with the engine on/key off.
I have never seen or even heard of this kind of failure, but in fairness, my daily drivers have always had carbureted engines until last year. Does anyone know if this type of failure indicates a shorted TCC solenoid? If so, I think I will just live without lockup for a while until this transmission is due for a rebuild. It's worked fine without lockup for over a year.
While doing a shakedown lap of the neighborhood, everything seemed normal, and then less than 1/4 mile from the house it simply quit. It seemed like an electrical failure, abrupt and instant, rather than sputtering to a halt like fuel starvation. A friend pulled me home, and I set about doing diagnostics. Just because it was rather simple, I used a 9V battery to fire the injectors while cranking the engine. It ran briefly. (I didn't try it for long.) Among other things, I checked the fuel pump - it worked when power was applied to pin G of the ALDL connector. Next I performed a visual check of the distributor, which was old. As bad as it looked, it may have been original to the Titanic. I replaced it reasoning that, due to its condition, it was time for replacement even without hard confirmation of a failure. No change.
One thing that seemed odd is that I didn't get a SES light at any time. Not when the engine died. Not when I was diagnosing (engine off, key on). Not at all. I even removed my instrument cluster and switched bulbs with a light that I knew was previously working. Still no SES light. This absence made me suspect that my ECM had failed. A used one with the same PN at the local pick and pull was cheap enough, and I swapped units, thinking that if it did solve the problem I would order a new one for the long haul, and have an extra "known good" ECM around for test purposes. No change.
While searching again online for ideas, I realized that I had missed step one. If it seems electrical, check the fuses. The first one I pulled was the ECM - bad. I replaced the bad fuse and drove out around the block several times. No problems. However, the next morning on my way to work it died again just like before less than 1/4 mile from the house. I caught a ride to work.
After work, I went back to the truck and examined the ECM fuse. It was bad. I pulled the fuse from a non-essential circuit of the same rating, fired it up, and drove home slowly. I replaced the fuse from the circuit I scavenged and let it run in the driveway for a while. No faults. I decided to attempt to make it fail again and observe anything I could about conditions or circumstances of the failure. I drove around the block five times with no fault or failure. Then I drove out of the neighborhood. In exactly the same location as the first time, it died again. This time (a) I had a pocket full of extra fuses, and (b) I realized that it was blowing the fuse just after the transmission shifted into 4th gear, and was ready to lock up the torque converter. I remembered the unplugged TCC circuit from before the repair. Since the lockup is activated only in 4th, I replaced the fuse, then drove the same route with the selector in 3rd. No fault or failure. I drove the route four more times without any incident. Finally, I dropped it back into 4th. Same fault, same location. I drove home, unplugged the connector, and have been driving a week without issue. Incidentally, with the connector unplugged, the SES light illuminates with the engine on/key off.
I have never seen or even heard of this kind of failure, but in fairness, my daily drivers have always had carbureted engines until last year. Does anyone know if this type of failure indicates a shorted TCC solenoid? If so, I think I will just live without lockup for a while until this transmission is due for a rebuild. It's worked fine without lockup for over a year.
