I have a Cat 3126 in a 1999 GMC 8500. The Allison went out and I put a reman transmission in today, along with a rebuilt starter. Now I seem to have engine problems. Truck starts fine. When the truck is moving at full fuel, the engine will sometimes derate and the check engine light will come on. It hasn't happened in 1st gear, but has happened in 2nd and 3rd, and often happens just as it makes the 2-3 shift. When its acting up I can't get it into 4th so I don't know how it behaves there. Get out of the fuel for 10 seconds or so and the check engine light goes out, get back on the fuel and it often runs ok for a few seconds to 10 minutes. The truck has a diagnostic port like a passenger car, but my scanner (and a local mechanic's snappy unit) doesn't do anything larger than a 1 ton pickup. It doesn't have or I can't find the round diagnostic port like a heavy truck uses. I'm hoping someone can give me suggestions about what component might be giving an intermittent fault that would cause the engine to derate and recover. I am terribly behind from the transmission going out and was hoping to work tomorrow.
Was the TCM replaced as part of the deal? The facts are not all lining up but I am kind of stabbing in the dark here that it might be Shift Energy Management (SEM) not operating correctly. Normally it communicates over the CAN link between the TCM and ECM when it wants to cut throttle during a shift. Probably a bad guess though.
The transmission is a MT653. I don't think it has any computer.
OK, I was thinking MD3060 with that model year.
You didn't kink or pinch a fuel line during the transmission swap? If not find someone who can scan it as it will cost less that throwing parts at it until its fixed.
Cat et with the obd adapter cable is what you need , i have 5 Chevy trucks i have to work on from 3126 to c7s.
I crippled it for a day working. It works most of the time in 1st, gets work done, just slow. Rained me out yesterday, and I found a mechanic with a scanner/cables that would read the machine. No stored codes. When it sets the check engine light the scanner says loss of vehicle speed signal, get off the fuel light goes out for a second to 5 minutes. I put in a new speed sensor in the transmission and it didn't help. So now I am looking for a wiring diagram to tell me where to find the other end of the wires to the speed sensor. Speedometer doesn't work at all, worked before the tranny swap. I've traced the wires as best I can and haven't found anything suspect yet.
Is the output yoke tight? When sensor was out did you check to see if you could move tone ring with a flat blade screw stick thru the hole.
Output yoke is tight, 200ftlb through a 4x multiplier. I will pull the sensor and check the tone ring.
walkerv, I owe you a bottle of holiday cheer! There is no tone ring installed in the transmission.
Well hopefully thats not a hard repair so much for a quality reman
That will do it