Medic0893
Newbie
I have a 1992 GMC C2500 with 5.7L Auto Trans 4L80e. I write this because the issues I encountered are common and the suggested resolutions are... precarious:
1. History: The motor (with TBI) went at 295K. No complaints. I got from a kid who beat the tar out of it, so I wasn't expecting much. When I got it he just got a rebuilt trans installed and I expected to have to replace the motor so I acquired a gently used crate motor which wound up spending 2 years on the engine stand, waiting patiently.
2. Engine/Carb Swap: I chose to replace the intake with a Holley 600 (electric choke, vacuum secondary) and manifold. Shorty Headers and true dual exhaust. Electric fans. HEI ignition (White and Purple/white wires must get the tach signal). I kept the original fuel pump and installed a regulator. Acculink TPS. Manual gauges (my kingdom for an affordable, functional water temp gauge).
3. Temperature Gremlins: Everything went smoothly. Started right up and ran good. Then it kept overheating. Parts cannon, aim fire... turns out the water pump fins disintegrated while it waited patiently. Notable at this point is concerning the two original temps sensors (manifold & Left head): The head sensor operates the original temp gauge, that got the manual gauge lead. The manifold sensor provides a signal to the trans for proper shifting. I say this because...
4. Trans Challenges: With the temp under control i was able to broaden my perspective and realized the trans wasn't shifting properly. A few experiments with the TSP sensor angle and it seemed good (all 4 gears)... but (nothing before the word "but" means anything) As I started driving it farther from home I noticed on the highway it would shift down on acceleration/hills then it wouldn't shift back into OD. If I shut it off and started it back up it would function normally until the next hill... I set out in search of enlightenment on this issue. I found a plethora of contributions (varying in efficacy). Make no mistake this was months of aggravation and frustration. This is where I learned the original manifold temp sensor has to be connected. It turns out the forward trans input sensor was bad (I swear I never touched it!!). I can't swear either way if it shifted correctly with the original motor, but I never detected this before the swap. Note: I'm not a big believer in coincidence, I'm just prayerfully hoping that is was indeed serendipity. Now it shifts no problems, up or down and back again.
I'm not suggesting this is the solution for every situation, but it has seemed for me.
At this point all is right with the world, but...
1. History: The motor (with TBI) went at 295K. No complaints. I got from a kid who beat the tar out of it, so I wasn't expecting much. When I got it he just got a rebuilt trans installed and I expected to have to replace the motor so I acquired a gently used crate motor which wound up spending 2 years on the engine stand, waiting patiently.
2. Engine/Carb Swap: I chose to replace the intake with a Holley 600 (electric choke, vacuum secondary) and manifold. Shorty Headers and true dual exhaust. Electric fans. HEI ignition (White and Purple/white wires must get the tach signal). I kept the original fuel pump and installed a regulator. Acculink TPS. Manual gauges (my kingdom for an affordable, functional water temp gauge).
3. Temperature Gremlins: Everything went smoothly. Started right up and ran good. Then it kept overheating. Parts cannon, aim fire... turns out the water pump fins disintegrated while it waited patiently. Notable at this point is concerning the two original temps sensors (manifold & Left head): The head sensor operates the original temp gauge, that got the manual gauge lead. The manifold sensor provides a signal to the trans for proper shifting. I say this because...
4. Trans Challenges: With the temp under control i was able to broaden my perspective and realized the trans wasn't shifting properly. A few experiments with the TSP sensor angle and it seemed good (all 4 gears)... but (nothing before the word "but" means anything) As I started driving it farther from home I noticed on the highway it would shift down on acceleration/hills then it wouldn't shift back into OD. If I shut it off and started it back up it would function normally until the next hill... I set out in search of enlightenment on this issue. I found a plethora of contributions (varying in efficacy). Make no mistake this was months of aggravation and frustration. This is where I learned the original manifold temp sensor has to be connected. It turns out the forward trans input sensor was bad (I swear I never touched it!!). I can't swear either way if it shifted correctly with the original motor, but I never detected this before the swap. Note: I'm not a big believer in coincidence, I'm just prayerfully hoping that is was indeed serendipity. Now it shifts no problems, up or down and back again.
I'm not suggesting this is the solution for every situation, but it has seemed for me.
At this point all is right with the world, but...