CAT 3116 Engine Speed Sensor

[DieselAddict]

First post here in this section. I searched around a bit to find the info on the engine speed sensor since the M1081 I recently purchased had a tach that didn't work. I didn't find a post with a concise breakdown of the problem so I decided to make one. I was thinking that the sensor was the likely culprit since the transmission shifted really hard.

First thing was to test continuity on the sensor and it was OPEN CIRCUIT where in the TM it indicates that the resistance should be less than 1440 ohms.

The sensor is on the bell housing at about the 10-11pm position if looking from the rear. You can see the bung it threads into here:





Upon removal it was obvious someone had NOT read the installation instructions.


Per another thread here on SS I read where there was a potential replacement. I ordered it from NAPA and it looked to be OK. The connectors were different but that is easy enough to take care of. I'm not worried about it being plastic since its not in an area where there are super hot things like exhaust. Its on the other side of the engine from that stuff.





I cut off the connector from the old sensor and soldered/heatshrinked it to the new sensor. Reinstalled per directions - thread in until it bottoms out then back off 2 turns and lock it down with the jamb nut.



To my delight the tach now works and after a 10 mile test drive the transmission is shifting a LOT better! I hope this helps if anyone else is in the same boat.

 

[Awesomeness]

To my delight the tach now works and after a 10 mile test drive the transmission is shifting a LOT better!

That sensor has no effect on transmission shifting, because it is connected to nothing other than the tach. You can verify this in the wiring diagrams. The transmission speed sensor is separate, and is located on the transmission housing.

 

[DieselAddict]

Thanks for the info. Am I reading this wrong? It looks like the engine speed sensor AND the vehicle speed sensor go to the transmission controller??

It was my understanding that the transmission needed engine speed, vehicle speed, and throttle position to work correctly.

 

[DieselAddict]

I think I see the difference. I see that the transmission has its own engine speed sensor in the bell housing on the right side.

 

[Awesomeness]

I think I see the difference. I see that the transmission has its own engine speed sensor in the bell housing on the right side.

Correct. Those schematics above are not the one you changed. The one you changed is on a different page, and is only wired to the tach.

 

[Guyfang]

In the norm, and MPU that fits the hole, will work. Its same for gen sets. Fits the hole, good to go. I am not a truck guy. What did your TM tell you to adjust the MPU to?

 

[Ronmar]

Guyfang, He mentioned it down in the pics. You screw it in till it touches a tooth then back it out 2 turns. You need to look inside the whole though and make sure you are directly over a rooth and not a valley. That sensor is pretty wide though so this might not be an issue with this particular one(I always look anyway).

If you are having issues with hard shifting, you can run the procedure used when replacing the throttle position sensor. It re-aligns the min and max TPS signal with the idle and full throttle positions and tells the transmission to re-learn the shift points. I believe it is in chapter 8…

 

[JD4044M]

I need the Output Speed Sensor for my 95 M1078 A0 to make my Speedometer work. I believe it goes in the Transmission???

 

[Ronmar]

I need the Output Speed Sensor for my 95 M1078 A0 to make my Speedometer work. I believe it goes in the Transmission???

That one is all the way back in the transfer case. On the back side there is a flat plate cover held on with bolts. It’s in there where it can sense a final output gear RPM. That sensor lookes like a key you would use to wind a clock…

 

[JD4044M]

I was going to look at my connection on mine. I was having intermittent Speedometer problems then it just stopped same with a new one. Do they sell new Sensor's if I need one? Is this the Connector for that Sensor on the Transmission?

 

[Third From Texas]

I was going to look at my connection on mine. I was having intermittent Speedometer problems then it just stopped same with a new one. Do they sell new Sensor's if I need one?

*see the OP

 

[JD4044M]

From what I see the Connection with 4 wires is the Speedometer one. I will have to look closer at this one and see if it has 3 or 4 wires?

 

[Guyfang]

Guyfang, He mentioned it down in the pics. You screw it in till it touches a tooth then back it out 2 turns. You need to look inside the whole though and make sure you are directly over a rooth and not a valley. That sensor is pretty wide though so this might not be an issue with this particular one(I always look anyway).

If you are having issues with hard shifting, you can run the procedure used when replacing the throttle position sensor. It re-aligns the min and max TPS signal with the idle and full throttle positions and tells the transmission to re-learn the shift points. I believe it is in chapter 8…

OK, didnt see trhat. The reason I asked, is because a gen set MPU adjust is almost the same, but not quite. We screw it down untill it bottoms out, then out 1.5 turns. Then we turn the engine over, while measuring AC Volts, at the MPU. What we want to see is between 2.5 and no more then 3 ACV for the best signal strength. I thought maybe your procedure would be the same.

 

[Ronmar]

OK, didnt see trhat. The reason I asked, is because a gen set MPU adjust is almost the same, but not quite. We screw it down untill it bottoms out, then out 1.5 turns. Then we turn the engine over, while measuring AC Volts, at the MPU. What we want to see is between 2.5 and no more then 3 ACV for the best signal strength. I thought maybe your procedure would be the same.

Yea, I don’t think there is anything about checking output voltage in the LMTV manual but it is easy enough to do. Most MPU,s should be able to make 2.5VAC pretty easilly.

 

[coachgeo]

Yea, I don’t think there is anything about checking output voltage in the LMTV manual but it is easy enough to do. Most MPU,s should be able to make 2.5VAC pretty easilly.

MPU = Magnetic Pick Up????

 

[Guyfang]

Correct.

 

[Ronmar]

I was going to look at my connection on mine. I was having intermittent Speedometer problems then it just stopped same with a new one. Do they sell new Sensor's if I need one? Is this the Connector for that Sensor on the Transmission?View attachment 837069

That is where the trans wiring harness connects to the transfer case internal pigtail. This connector is on the front side of the transfer and if dirty/corroded could cause you speedo issues. The access cover for the sensor itself is around on the backside of the transfer case. The sensor is probably only 2 wires, so the other wires on this connector may be for some other purpose(some other sensor?)

 

[JD4044M]

Great Thanks, I am having some medical issues with my Pancreas and there looking for cancer? Been rough working on the truck and I still have my fan and alternator to put on, have not forgot to say how it worked out. Least I get to drive it for fun. I just need to be out of pain long enough to jump in and do these 2 easy jobs. A CT Scan is on the list real soon to let me know more what is going on. I have my fingers crossed!!

 

[ramdough]

Great Thanks, I am having some medical issues with my Pancreas and there looking for cancer? Been rough working on the truck and I still have my fan and alternator to put on, have not forgot to say how it worked out. Least I get to drive it for fun. I just need to be out of pain long enough to jump in and do these 2 easy jobs. A CT Scan is on the list real soon to let me know more what is going on. I have my fingers crossed!!

I wish you the best of luck and good health. Hopefully they find something easily curable.


Sent from my iPhone using Tapatalk

 

[coachgeo]

... I have my fingers crossed!!

we are crossing ours too