I always hate doing this intro stuff but I understand the necessity
Anyway, my name is Mike and I work for a John Deere dealership. A lot of what I do deals with the electrical portion of the machines, it seems I'm the go to guy for shorts, opens, CAN bus issues and so on and so forth. Just when I think I've seen it all, there stands before me a 4730 sprayer with a 6.8L Tier 3 emissions with Level 16 engine controller. I've seen and diagnosed almost everything this engine can do, or not do but this one has me and John Deere's technical assistance (DTAC) absolutely stumped. What's happening? The ECU is throwing a code for the cam position signal error and shows signs of either electrical interference or mechanical issues causing the erroneous reading of the cam sensor. I've tried everything and have come to the conclusion the only way I can diagnose this machine is with an oscilloscope. You see the computer actually detects there is noise on the signal wire but I cannot see anything but the output to my laptop, which resembles a seismograph reading of an 8.5 earthquake. I need to find out if it's electrical interference by identifying the intruding signal or if it's mechanical by observing the sine wave created by the sensor. Here are some things that I know:
1) The signal for the cam sensor is rotating at half the speed of the crankshaft and the tone wheel has a special identifier on the tone wheel for TDC #1.
2) The engine is a 6 cylinder, therefore there are 6 markers on the tone wheel and the engine max RPM is around 2300. With the camshaft rotating at half the speed of the crankshaft, it is 1150 RPM x 6 identifiers= 6900 pulses per minute, correct??
3) The signal voltage input is either 5 VDC or 12 VDC. I should know this for sure but I can't remember off the top of my head.
The sensor is a magnetic input type. It gets voltage supplied on one side and sends out a square wave signal on the other wire.
What I would like to accomplish
1) Observation of the sine wave while operating the machine.
2) Isolating any noise I may find on either the a) signal wire or b) power supply wire to the sensor.
3) Optional but would be nice to simultaneously observe the a) camshaft signal and input b) crankshaft signal and input.
I know if I dropped 10k on an oscilloscope I could get the job done but I need to do this on a budget, a tight one. Honestly I may never use this thing ever again, then again once I learn how to use it, I may use it all the time. I'm drawn to the USB scopes on the market due to their compact design, interface with a computer and have an appealing cost to someone who is not intending to scratch the surface of the capabilities of the scope.
Other considerations: I may be inclined to spend a bit more on a better one as my children show interest in electronics, such as robots and things of that sort. Heck, maybe I could actually repair a TV that has more than the capacitors blown out.
Thanks in advance. I appreciate your time, knowledge and input into my decision on this new purchase. If this goes through, I will be seeing you in the oscilloscope forums!!!