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700k Dozer cam sensor problem

Discussion in 'Dozers' started by HFservicesNC, Apr 7, 2022.

  1. HFservicesNC

    HFservicesNC Member

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    Jan 21, 2013
    Messages:
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    Location:
    Chapel Hill NC
    I bought a 700k dozer back in 2019 used that had dropped a valve. I had my mechanic at the time rebuild the engine and get the machine operational. After rebuilding the machine and getting it going it had a camshaft sensor error that we believed to be in the wiring. We ran it like that for a while until here recently It started to derate the machine. You could clear the code and it would run like it was supposed to for 10 to 15 minutes and then derate again. I replaced a cam position sensor which did not fix the problem. I got tired of dealing with it so called our local John Deere construction equipment dealer and had them come out to look at it. The John Deere service tech replaced the cam position sensor, Ran wires directly from the cam sensor to the ECM and tried a Donor ECM with no change. They then recommended that I bring the machine in for them to tear the front half of the engine apart since they believed it was a problem with the camshaft gear that the sensor reads. Today my mechanic and I pulled the fuel pump that gives access to the camshaft gear and didn’t see any problems. I then went ahead and replaced the crank sensor for good measure since the dealer didn’t Mess with the crank sensor. I checked all wiring and connections from the crank and cam sensors to the ECM and everything checks out good. I cleared all the codes and ran it with the same result. ECU code 636.10 - cam sensor pattern error. I logged in to the troubleshooting menu and observed the cam and crank rpm. The crank rpm would hover around 900 rpm at idol and the cam would do about the same but a lot more erratic. After watching it for a couple minutes I noticed that the cam rpm would randomly spike up to 3000 RPM and then drop back down to 900 and then spike back up to 3000. I am thinking the dealer may have been wrong about the ECM and that is actually the problem but they still want me to Bering it in for them to tear the front gear cover off. Anyone have any suggestions or thoughts?
     
  2. nowing75

    nowing75 Senior Member

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    if the pickup did not look damaged or loose i would see if you could find someone with a scope to look at both signals.
     
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  3. JakeRanisate

    JakeRanisate New Member

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    Lakeland, FL
    You said your mechanic at the time rebuilt the engine after it dropped a valve. Did that involve changing the cam, or gears, etc? In other words, is there a chance that the cam gear itself is incorrectly positioned on the cam? Correct me if I'm wrong anywhere here, my experience is primarily with Cat. I know the position sensor has to run very close to the cam in order to read correctly. If the gear was not seated fully on the cam, the sensor may not read right.
     
  4. mg2361

    mg2361 Senior Member

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    Complete serial number?

    Was the injection pump properly timed since the cam sensor actually reads off the back of the injection pump gear? Cam gear tight? Tone wheel tight on the crank?

    Do you have anything aftermarket installed? Two way radio? Some other device that is not standard?

    You could still have a wiring harness issue. Did the tech who ran the separate wires twist those wires nice and tight? If not, then running the wires loose (parallel to each other) subjects them to interference. The signals from the cam and crank sensor are very weak signals and need to be twisted together and/or shielded.

    I agree with nowing75 that a scope could be a big help here.

    Below is from the same family of Deere engine with a loose tone wheel (blue trace). Cam was good (red trace). Timing was spot on.


    Loose Tone Wheel.png
     
    Last edited: Apr 9, 2022
  5. HFservicesNC

    HFservicesNC Member

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    Jan 21, 2013
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    Location:
    Chapel Hill NC
    We did not change the cam or cam gears. John Deere entertain the idea that the gear may have spun on the cam but started backtracking when I stated the sensor reads the cam gear not the cam so it wouldn’t know the difference if it did spin as long as the cam gear is still in time with the crankshaft gear. I just got off the phone with John Deere dealer and they still seem to think it’s an electrical issue But they do not think it is the ECM. With the engine off there is no deviation in the rpm on either sensor they both read 0rpm. I just changed the pins on the ECM connector and no change.

    I have Topcon GPS machine control with UHF radio but it dose it even when its off and disconnected. The dealer did not twist the wires so I will twist them and see if that changes anything. I thought the cam sensor reads the cam gear from what I saw when we pulled the fuel pump and there is no need for fuel pump timing since it is common rail but I may be wrong.The cam gear seams to be tight and has very little thrust.

    What in the blue trace indicates a loose tone ring? If I get my hands on a scope do I tap on to the cam wires and run it? I did figure out it will run without the cam sensor connected and so far does not derate the machine.

    Machine serial number 1T0700KX FE259297
    Engine Serial Number PE6068R068167
     
    Last edited: Apr 9, 2022
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  6. mg2361

    mg2361 Senior Member

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    Actually, I had a brain fart:(. The cam sensor actually reads notches on the back side of the "upper idler" gear, which is between the cam and the high pressure pump. The sensor is mounted on the High Pressure Pump's mounting adapter. So, gear timing could be an issue.

    Since this code appeared since the engine has been repaired makes me wonder if the gear train is properly timed.

    Actually, it is very important to time the High Pressure Pump. You want the pumping plungers to be at top of their stroke when the piston is at TDC and the injector is firing. There is a timing procedure for that pump in the manual.

    Amplitude.png
     
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  7. HFservicesNC

    HFservicesNC Member

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    Ok I have hooked up a scope before and after twisting the wires with no change. I used a signal generator to feed the ECM a sine wave at 97 htz and the machine reads it as a cam shaft rpm of 900. It does not fluctuate any making me think deer is correct in saying it’s not the ecm. With the camshaft sensor wires completely disconnected from the ecm and machine running I hooked the scope to the camshaft sensor wires. Remember this is my first time using a scope But it looks to me there is a random blip in the sine wave. I’m really not sure what’s causing this at this point since even if it was out of time it should have a consistent sine wave since it’s just reading the cam gear.
     

    Attached Files:

  8. mg2361

    mg2361 Senior Member

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    I still suspect assembly issue since it started when rebuilt.

    You have a 2 channel scope. Connect a lead to each signal wire of each position sensor (by backprobing) and to ground. We should be able to see if they are timed correctly by looking at the signal pulse from each sensor.

    Sync Pulse.png
     
    Last edited: Apr 11, 2022
  9. HFservicesNC

    HFservicesNC Member

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    Location:
    Chapel Hill NC
    Do you see a problem with the sine wave in my pictures? If you don’t then I understand why I need to check timing. If my sign wave looks bad then I don’t see how the timing is relevant currently until I can figure out why my cam gear / sensor is giving a bad reading.
     
  10. mg2361

    mg2361 Senior Member

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    In the 3rd picture , yes I do. In the one where you are pointing to the sync pulse, that one looks perfect. I am not familiar with that scope and it's settings so I am not sure what to make of the 3rd picture. Also, I am by no means a scope expert. I have had one for 5 years now and I am still learning. You said you were connected to the wires that were unplugged from the ECU. All that tells me is you have an issue with either the wiring, sensor or tone wheel. Does not accomplish much. If you perform the task as I mentioned by backprobing both sensors, then we can see if the signal improves at the sensor, which would eliminate the sensor/tone wheel. If it does not improve, then the issue is sensor/tone wheel. It will also confirm or deny cam/crank timing as well.

    Also note that one of the first steps in your codes diagnostic tree is to check timing. If timing is off it should throw a out of sync code, but the possibility has to be eliminated.

    And it still comes back to: it wasn't an issue before the rebuild.

    Scope Image.png
     
    Last edited: Apr 12, 2022
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