**UPDATE** I've taken a screen movie with the scope in action and uploaded it.  - Page 1
Forum section: electronics / beginners

author: dieseltech82
author_rank: Contributor
timestamp: May 29, 2015, 03:48:04 pm
content: So I've been playing around with the shops new scope trying to diagnose a sprayer setting an active cam sensor code. In my setup I want to monitor the signal at the cam sensor and at the ECU. I have no real reason to do this other than making sure there is no diviation in the sensor signal. In my attempt, I crossed my wires for the sensor. This resulted in the code becoming active, my signal on the scope was very noisy and had no properties of a sinusodial wave. Good new though, I figured it out and am going to try to get some relevant data to finally get the problem pinned down. I'm going to try and attach a screen shot of my laptop. Channel 1 is at the ECU, Channel 2 is at the sensor and the FFT is looking at my channel 1. I may put the FFT on channel 2 as well. Enjoy!**UPDATE**I made a screen movie of the scope. I uploaded the movie here:I'm not exactly sure what's going on and why the sine wave is bouncing back and forth like it is. It could be because it has a fault and that is the fault showing up in the sine wave. If this is the case, the problem looks to be more mechanical than electrical. Do my parameters look correct? Should I modify something? Any help would be greatly appreciated as I learn how to use this device. Thanks in advance for your time.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 30, 2015, 02:48:43 pm
content: Well, at first glance I see two things. First, your trigger level is set to a level where the signal is nearly horizontal. (Trigger level symbol is on the right side of the waveform display area). Try moving the trigger level up so that it's looking at a portion of the signal that has a definite strong rising slope. This may allow a more stable capture of the signal.Second, there is that small peak every 12th cycle. Is this some kind of "zero" indicator for the cam position? In any case the spacing (time) to the next positive peak is greater than the spacing between the rest of the regular positive peaks. (The negative peaks are all at regular intervals.) I don't know what it's supposed to look like so I can't tell if this is a problem or not. Can you take a trace from a known good unit for comparison?

author: max_torque
author_rank: Super Contributor
timestamp: May 30, 2015, 03:06:46 pm
content: Does it have a 12 tooth trigger wheel on the cam? It definitely looks like every 12th "tooth" is damaged or contaminated in some fashion? (assuming as previous poster mentioned it's not mean't to be like that, which would be unlikely on a CAM sensor (but possible on a CRANK sensor as you need to know TDC)

author: HighVoltage
author_rank: Super Contributor
timestamp: May 30, 2015, 03:14:19 pm
content: You need to look also at the signal polarity.It is shown correctly in your video, but it also depends on which side of the sensor you hook up the probe.I had it in the past, that an inductive sensor like this one was wired wrong inside and the signal was flipped.This resulted - of course - in a time delay that was engine speed depending and caused some real problems.My client at the time was a large OEM and this problem slipped through the quality control.

author: dieseltech82
author_rank: Contributor
timestamp: June 01, 2015, 06:18:57 am
content: Quote from: alsetalokin4017 on May 30, 2015, 02:48:43 pmYes, there is a mechanical indicator on the idler gear that the position sensor reads to indicate TDC #1. This is a inline 6 cylinder engine, so I'm not sure why there is 12 identifiersI'm going to attempt to get a good capture in the morning with video to help DTAC assist in my case. They want a good capture of cam/crank sensors to see if it is in time. If it turns out the engine isn't in time, I'm going to be......discouraged as another technician had the front cover off to verify timing.

author: dieseltech82
author_rank: Contributor
timestamp: June 01, 2015, 06:22:10 am
content: Quote from: HighVoltage on May 30, 2015, 03:14:19 pmI will look into the signal polarity to ensure it's correct. I didn't think it was gong to be a big deal, since this is an A/C sine wave. I could see it effecting my reading when comparing cam/crank signals to ensure the timing is correct. So unless my brain says otherwise, I will double check my polarity. Also on a related note. Are there any wire piercing probes that you guys would recommend? I used some really nice Flukes (repackaged Pomonas) and I like them alot. The only problem is they are 50/pair

author: daybyter
author_rank: Frequent Contributor
timestamp: June 01, 2015, 08:35:49 am
content: The yellow marker at the right side of the screen has a 'T' on it. That is your trigger level. The scope syncs the trace to this signal level. Move it up by some voltage.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: June 01, 2015, 01:30:24 pm
content: Quote from: dieseltech82 on June 01, 2015, 06:22:10 amFirst, the voltage issue. The voltage shown on the scope may be correct; we can't tell from here if you have probe attenuation and scope probe settings correct. Or even if your probes have adjustable attenuation. Is there a "1x/10x" switch on the probe? Is there a setting to match in the scope software?Second... it is _not_ really an "AC sine wave". Look at the horizontal spacing of the top peaks vs. the bottom peaks. You will see that the top peaks have a slight delay after the small location pulse, but the bottom peaks do not. If you have the signal wires (polarity) reversed from what the control unit is expecting or needing, this difference may make a difference. I see that the Trigger Value is given as a positive number but the Trigger Level indicator mat be at or below the channel baseline. This makes me wonder if you have a channel inverted in the scope. Also, in general for the Input Coupling we would use DC coupling rather than the AC coupling you've got set, unless there is a specific reason for using AC coupling. Don't make the mistake of thinking that "AC coupling" is "for AC signals" -- AC coupling removes DC offset information, and may conceal an error like having the wires swapped from what they should be.Third: The trigger issue. I've marked up your screenshot to show the relevant trigger indications, and where I'd try setting the trigger to obtain a stable display. Once you've got a stable display you should be able to "zoom" the horizontal timebase to show a single period, and change the "trigger delay" or "horizontal delay" (however your scope terms it) to scan horizontally until you find the exact peak that you want to look at.Some scopes, like the Rigol DS1054Z, have trigger options (Runt, Nth Edge, etc.) that could cause the scope to trigger precisely on the small indicator peak instead of the "ordinary" larger peaks.Wire piercing probes? For quality, stick with the Pomonas. On a budget (like me).... use a large sewing needle and the scope probe's springhook tip .....As far as troubleshooting goes.... I have been burned several times by accepting information from "another technician" when troubleshooting various systems. I've learned to start from the beginning, no matter what someone else who worked on it before might say. Here's a laugh: I used to work in an aircraft engine overhaul facility. Some piston aircraft engines come in "matching pairs", one rotating CW and the other rotating CCW. One day we had one on the test stand that just wouldn't start no matter what. Pulling covers showed that the valve timing was all screwed up. I went to the BOM records looking at part numbers, and discovered that the build-up mechanic had been issued... and had installed... a "left turning" camshaft in a "right-turning" engine. Fortunately this is not an interference-type engine and nothing was damaged, other than the ego of the build-up guy, who had to tear it all apart and rebuild it again with the "right" part...

author: dieseltech82
author_rank: Contributor
timestamp: June 01, 2015, 01:40:13 pm
content: Quote from: daybyter on June 01, 2015, 08:35:49 amAwesome, I'm doing this now and it's working very well. I moved the level to almost 10 V and it's helping a lot. Thanks!

author: dieseltech82
author_rank: Contributor
timestamp: June 01, 2015, 01:47:17 pm
content: Quote from: alsetalokin4017 on June 01, 2015, 01:30:24 pmI've done the adjustments as perscribed. You are making me look like a pro! Thanks!. I'll attach the new video I make. I've got my GO pro with me to help DTAC see/hear what is going on. Thanks again! You are correct on not trusting what others tell you. I have been bitten more than once by well to do technicians

author: dieseltech82
author_rank: Contributor
timestamp: June 01, 2015, 02:13:01 pm
content: On another note. I am not using the provided probes, so my attenuation would be 1x? I'm backprobing the sensors. I just noticed that If I leave the signal plugged in and remove the other one, I still have a sine wave. I installed the test equipment like I did from referencing several YouTube videos on crankshaft/camshaft diagnostics.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 01, 2015, 08:22:15 pm
content: Quote from: dieseltech82 on June 01, 2015, 06:22:10 amSignal triggering in the cars computer is usually done at the time when the signal goes from positive to negative at a level of about -0.5 Volts.On your signal above, this is correctly happening at the steep part when the polarity is changing.If the signal would be flipped, the slow part of the signal would reach -0.5V first, but the trigger point is too early and can cause some real damage on some engines, especially at high engine speeds.

author: dieseltech82
author_rank: Contributor
timestamp: June 02, 2015, 02:58:58 am
content: Quote from: HighVoltage on June 01, 2015, 08:22:15 pmI hooked the test leads as follows: The scope signal wire to the ECU signal wire and the ground lead to ground. Before I had the ground lead on the signal return wire. My readings looked the same but what I noticed is that I only needed the one wire hooked up, so I took the scope ground to a good ground point on the machine. I ended up with my trigger point close to 18V, maybe a little more to get a readable graph. The downside was the machine could not trigger when the engine was loaded and RPM's dropped. I tried the auto trigger function but the graph it displayed moved around a lot. What is needed is the ability to have an auto trigger function based on % of peak voltage. That way the trigger can move and still have a discernible graph.

author: daybyter
author_rank: Frequent Contributor
timestamp: June 02, 2015, 07:45:53 pm
content: Or just stop the acquisition and analyze the signal then?

author: dieseltech82
author_rank: Contributor
timestamp: June 02, 2015, 11:43:18 pm
content: Quote from: alsetalokin4017 on June 01, 2015, 01:30:24 pmI fixed the machine today and two of you were able to help me correctly diagnose the machine. When I retired the crankshaft sensor, I reversed the polarity. Strange enough, my fault code remained the same, along with the hesitation and strange can signal reading using Service Advisor. This mess one of two things. 1) the original sensor was also polarity reversed or I did have a fault with the cam sensor and or crank sensor wiring and induced a new fault that acted exactly like the original fault. This is what made the diagnosis so hard. I thank you for all of your input. I have another question. How can you tell the polarity was reversed? I made videos of my screen while testing but YouTube is taking their precious time processing them. If they ever process, I will update the thread. I didn't capture new data after the repair. I simply drove it and didn't get the code or hesitation. The diagnosis is bittersweet and a reminder that no matter how long you've been doing something, there's always room to grow. Thanks again!!

author: dieseltech82
author_rank: Contributor
timestamp: June 02, 2015, 11:46:50 pm
content: Looks like YouTube did post it sometime today.http://youtu.be/G810KefCAcE

author: tautech
author_rank: Super Contributor
timestamp: June 02, 2015, 11:56:27 pm
content: Interesting.I've followed both your threads looking for info from you to contribute some worthwile advice and not once did you indicate you had replaced the camshaft sensor.I and probably others no doubt thought we were trying to help you find the faulty culprit, sensor or otherwise.I even asked if you had swapped out the sensor and you didn't grace me with a reply.Only now have you indicated :QuoteWell good you have it sorted.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 03, 2015, 09:07:00 am
content: Quote from: dieseltech82 on June 02, 2015, 11:43:18 pmBecause it happens all the time.I have seen this problem even at OEM level here in Europe. I was hired for a job to fix a severe problem and it turned out to be a reversed polarity inductive sensor. It was kind of embarrassing to the OEM, flying me out for this quick analysis.

author: fubar.gr
author_rank: Unknown
timestamp: June 03, 2015, 09:14:23 am
content: Quote from: dieseltech82 on June 02, 2015, 11:46:50 pmCan't see the video, says it's private

author: dieseltech82
author_rank: Contributor
timestamp: June 03, 2015, 10:59:26 am
content: Quote from: fubar.gr on June 03, 2015, 09:14:23 amI just checked it and it says that it's public. I'm not YouTube expert though. Perhaps it wasn't fully available? It does say it's under review. Seems like a lot of steps to have a video displayed on YouTube.

author: dieseltech82
author_rank: Contributor
timestamp: June 03, 2015, 11:13:58 am
content: Quote from: tautech on June 02, 2015, 11:56:27 pmI apologize for not replying to your question. I had to go back and read to see because I thought I had given a reply on the sensor. The sensor itself it used in several John Deere engines and is the failure 99% of the time, so it was first off the list. As far as me contributing worthwhile advice, I'm a noob to electronics. Now if we are going to talk strictly electrical troubleshooting, I've got you coveredThanks for participating in the discussion and providing input to help me diagnose the case. I did inform my manager that the fault was positively identified using the scope, which made him feel a lot better about the purchaseI'm going to keep searching and studying so I too can identify a sine wave with reverse polarity. With today's advanced computer and electronics in the emissions and engine monitoring systems, it will be invaluable.

author: dieseltech82
author_rank: Contributor
timestamp: June 03, 2015, 11:16:31 am
content: Quote from: daybyter on June 02, 2015, 07:45:53 pmI wanted to be sure I have "good' data so that whoever I ask to read it, will be able to do so. I worked in predictive maintenance for years and that was a focus of our group, that way the data was repeatable and useful for other people for years to come. Since I was unsure of weather or not I had useful data, I kept at it.