Hi to everyone, I am new to posting but have followed this forum for a few years. I am working on a 750c serial number T0750CX82133, with “x” being unreadable. I replaced the speed sensor on the pump and can’t get calibration started. I’ve adjusted my idle speed to 1050 and my decelerate down speed to 900rpm. When I start calibration I get “4e” flashing but the only way to get it to stop flashing is to bring rpm’s to just over 1500. I have the tm 1588 and 1589 manuals and I know this is not what’s supposed to be happening. Once “4e” stops flashing the “4” will go away but Iam always left with the “e.” I’ve tested all the rotors sensors, I don’t know what I am doing wrong and any help would be greatly appreciated.
Welcome to HEF kcory ! Is this an old Hertz machine? If so the lastt digit would be a "7". When keying on, which controller version cycles through the screen, 556, 600, 700, or 800? Why was the pump speed sensor replaced? When you replaced the pump speed sensor, did you check that the speed ring is in the center of the hole and not loose? You should have been able to touch both sides of the speed ring with a screwdriver. Adjust all your engine speeds with an injection line pulse tach, not with the dash tach. Set all your speeds to the middle of spec and not the high or low ends of spec. Retry your calibration and post the results.
Ok, so I hooked up the vacuum pump and try to check the speed ring and I’m not sure what I’m supposed to feel but it doesn’t feel loose. I’m guessing the speed ring must be like an inch thick. I can’t really tell with the screwdriver I thought maybe it was just a thin ring but mine feels like it’s quite wide. I couldn’t feel the magnetic thing with my screwdriver either.
Did the machine move before the speed sensor replacement? Why was it replaced? The speed ring in about a 1/2 inch wide. A screwdriver will not magnetically stick to it. I doubt this is an issue since it is extremely rare for the speed ring to move. How did you adjust the speed sensor gap? Again, try what I mentioned above.
Ok, thank you again. I will try to find an injection line tach and adjust my rpm from that. The reason I replaced pump speed sensor was that it had a code saying there was a problem with pump speed sensor. The machine moved in reverse slowly, and forward barely. As soon as you increased rpm over 1200 or so it will stop moving in any direction. When this all started the dozer went from working fine at any throttle to having to give it less throttle for it to continue working until finally barely moving at slow idle. Works better in reverse but not much
Quick question, does fast idle mean wide open which is 2250rpm?
Yes.
When you replaced the speed sensor did you adjust the air gap correctly?
Well I think I adjusted it properly. I ran it in finger tight, backed it out half turn.
Your adjustment is correct. But I have had this happen to me,the glam nut and o ring can give you a false sense of contacting the speed ring. I have learned to back the gland nut and o ring up the speed sensor shaft. Tha when you contacted speed ring look for clearance between pump case and o ring.