Engine speed sensor question

samsneed

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I was doing this by myself, so I had to start the engine to measure. I had installed it to 2 turns back from bottomed out in contact, as the TM said. I was reading 0.025VAC, with the engine running. I turned it in to about 5/8 turn backed out, and am now reading 0.260VAC with the engine running. This was a used RPM sensor I bought from Suprman. Any idea if those readings are ok?
I've read that less is more when it comes to those readings, if the tach works at 2 tyrna, why risk running it closer

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Awesomeness

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I've read that less is more when it comes to those readings, if the tach works at 2 tyrna, why risk running it closer
Because I don't have a tach, and the truck isn't working correctly. I swapped engines, and during the swap we broke the engine speed sensor. Now the truck shifts way harder, especially down, than it used to. So I'm actually trying to figure out what's wrong, and it seems like a good explanation that the transmission isn't aware of the engine RPM.
 

Suprman

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The output speed sensor on the trans is a common failure item. Sometimes it will be a bit off and not throw a code. It's an inexpensive easy part to replace.
 

Awesomeness

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The output speed sensor on the trans is a common failure item. Sometimes it will be a bit off and not throw a code. It's an inexpensive easy part to replace.
Before the engine swap, it seemed to shift at appropriate speeds. It would shift up into 7th gear by maybe 40-45MPH (in 7th while driving around town), then down at a lower speed that felt ok (maybe 35-40MPH?). I don't really know what it was doing, because it wasn't noteworthy. I just know that after the engine swap it is very different. Now it doesn't shift up to 7th until exactly 50MPH, when the engine is at a screaming RPM, and it shifts down to 6th at the exact same 50MPH point (and the truck jerks while the engine tries to catch up to that high RPM again). I assumed that because we didn't touch the transmission, just the engine, throttle linkage adjustment, and broke the first engine RPM sensor, those would be the most likely culprits. Does that problem sound more like the output speed sensor on the transmission?
 

Suprman

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Does it give you any codes now? There is a throttle position sensor on the engine also. I believe there is an adjustment procedure in the tm for it.
 

Awesomeness

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Does it give you any codes now? There is a throttle position sensor on the engine also. I believe there is an adjustment procedure in the tm for it.
No, no codes. And I followed the throttle adjustment procedure in TM, I'm not sure if that covers the throttle position sensor adjustment too. The procedure had me loosen the throttle until it contacted one stop, then floor the pedal and adjust it until it touched the other stop.
 

Awesomeness

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I believe there is a specific adjustment for the tps. Probably in the repair tm under replacement of.
Thanks, I'll check for it.

What's your thinking here? I have my foot off the gas to slow down, the TPS can't tell that, and so it downshifts early while it's still at too high a speed (and then the RPM jump up)? If it could tell it would know to wait longer?
 

Suprman

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The trans computer uses the 3 sensors for combined input. Anything being a bit off can affect the shifting. Since you swapped the motor I would think the tps could benefit from alignment. I believe the engine speed sensor signal is counted as pulses. So slight voltage variations may not matter. I believe the trans computer has some learning capability also so it can automatically adjust itself a bit.
 

Awesomeness

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WTEC II/III Transmission and Throttle Position Sensor Calibration: WTEC II TEPSS requires calibration after replacement. Procedure found in TM 20-3, page 8-5 (p 637). Procedure for WTEC III is similar, and is in the manual on page 8-7 (p 639) immediately following the WTEC II procedure. The Throttle Position Sensor procedure is also the same, and found on page 4-18 (p 114).
- Position master power switch to on and wait for Neutral (N) indication from WTEC II TEPSS (TM 9-2320-365-10).
- Position master power switch to off (TM 9-2320-365-10).
- Perform steps (2) and (3) four more times.
- Position master power switch to on and depress accelerator pedal all the way to cab floor (TM 9-2320-365-10).
- Start engine (TM 9-2320-365-10).NOTE: Transmission shifting may be rough until WTEC II TEPSS determines proper shift points. Operating vehicle through each gear range several times will allow WTEC II TEPSS to determine proper shift points.
- [From WTECIII procedure only] Check VOLTS gage for charge indication (TM 9-2320-365-10).
- Operate vehicle through all gear ranges several times (TM 9-2320-365-10).
- Shut down engine (TM 9-2320-365-10).
 

Awesomeness

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I finally had a chance to use the above procedure to recalibrate the throttle position sensor and transmission. It worked like magic. The transmission shifts really well now, up and down. It even stays in 3rd until the truck has come to a complete stop for 1-2 seconds, which is nice because it eliminates the biggest ratio downshift most of the time. I'm really happy with the results.

Just for information, my transmission is filled with ATF.
 

Tap5430

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On the Cat 3116, there is an engine speed sensor (part 4) screwed into the driver's side of the bell housing (TM 9-2320-365-20-3, 7-38, Page 406). Two questions...

1.) Are replacements available? Is it a military or civilian part?

2.) What does it do? Is it only used for a tachometer (which I don't have), or does it do other things too?

I'm replacing the engine, and mine appears broken (fine copper wires unraveling out the nose of it). I'm curious if I'll be able to get the new engine running without one, or do I have to get it replaced before I can start it up.

Thanks!
View attachment 686468
 

Tap5430

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Thanks for all that you have contributed to this Forum . What a asset to find this information. My tach. went out after my son had something welded on our M35A3. Don’t no if it this could cause outage. My experience with this type of sensor is with generators (mag pick up) some time’s just cleaning and reinstalling does the trick. Will be on this TM. this afternoon.
 

BERZERKER888

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WTEC II/III Transmission and Throttle Position Sensor Calibration: WTEC II TEPSS requires calibration after replacement. Procedure found in TM 20-3, page 8-5 (p 637). Procedure for WTEC III is similar, and is in the manual on page 8-7 (p 639) immediately following the WTEC II procedure. The Throttle Position Sensor procedure is also the same, and found on page 4-18 (p 114).
- Position master power switch to on and wait for Neutral (N) indication from WTEC II TEPSS (TM 9-2320-365-10).
- Position master power switch to off (TM 9-2320-365-10).
- Perform steps (2) and (3) four more times.
- Position master power switch to on and depress accelerator pedal all the way to cab floor (TM 9-2320-365-10).
- Start engine (TM 9-2320-365-10).NOTE: Transmission shifting may be rough until WTEC II TEPSS determines proper shift points. Operating vehicle through each gear range several times will allow WTEC II TEPSS to determine proper shift points.
- [From WTECIII procedure only] Check VOLTS gage for charge indication (TM 9-2320-365-10).
- Operate vehicle through all gear ranges several times (TM 9-2320-365-10).
- Shut down engine (TM 9-2320-365-10).
hmmmmm... I bet since my retran this procedure was never done . ..question ..the second to last step advised power switch on.. depress pedal...

the final step is to start the engine.... while the pedal is depressed to the cab floor? or is it meant to be started in the normal fashion with no pedal to the floor .?
 

Awesomeness

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hmmmmm... I bet since my retran this procedure was never done . ..question ..the second to last step advised power switch on.. depress pedal...

the final step is to start the engine.... while the pedal is depressed to the cab floor? or is it meant to be started in the normal fashion with no pedal to the floor .?
I interpret it as push it and release it, then start. But that's why I included the references in parentheses, in case you want to read it yourself. That procedure I wrote in created by stitching together several different parts of the puzzle, from different places... otherwise it's hard to follow or know what to do at all. Gotta love military TMs.
 

BERZERKER888

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I interpret it as push it and release it, then start. But that's why I included the references in parentheses, in case you want to read it yourself. That procedure I wrote in created by stitching together several different parts of the puzzle, from different places... otherwise it's hard to follow or know what to do at all. Gotta love military TMs.
thanks much.. I'll give it a push and go before I fire it up .
 

Awesomeness

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thanks much.. I'll give it a push and go before I fire it up .
In thinking about it further, I may just be doing the press-and-release interpretation because old '70s carbureted engines needed that press-and-release to reset the choke before starting. Obviously that doesn't apply the same here.
 

Ronmar

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It is press and release, then start. After the correct number of power cycles clears the TPS cal and shift schedules, The throttle press and release re-educates the TCU to the current min and max throttle position Points. it can then provide 0-100% throttle position info to help determine smoother shift points and kick downs based on driver intent. Without this, the trans shifts based on it’s minimum and maximum RPM set-points for each gear range which can be a little harsh.

The TCU can now also use these new min-max throttle position points to help determine if the throttle position sensor has issues which indicate readings outside the calibrated min and max positions set by this procedure.
 
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