Hi, All:

Okay, I'm a new guy in the block, doesn't mean I can beat you someday later, does it?:-) Tom, I appreciate your fast shiiping.

I'm a MB dealer tech. Recently, there are repeated cases about new MB 272, 273 engines' Camshaft problems. Mainly, MIL on with Cam sensors problems or ME (ECM) reports variable cam timing not right. I don't think I understand the reason, thus trying to probe a little more into it.

I'm trying to establish some reference for later. This is a new vehicle ML164 with 4 miles on the clock, I'm doing a PDI (Pre Delievery Inspection), no problem (what would you think otherwise?:-). I was told base Cam timing should be lined up. True? Or my scope setting not right?

Thanks,

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Hi George,

Excellent PicoScope 5 capture.  You have 78,125 samples per channel there with a 6.4 microsecond sample interval.  Channel time offset on the 3000 series is always 50 nanoseconds, regardless of sample rate.  For all practical purposes, this is simultaneous.  The only time channels won't be in sync is if you choose alternate sampling, which you have not.

I am not at all familiar with this application but usually VVT engine controllers look at CKP/CMP shifts to monitor the cam timing changes.  Might want to snag some examples of CKP/CMP relationships.

Perhaps one of our resident experts would have some input on this system.

Welcome to the forums.  The General Public Area forums are great for general public discussion on many topics.  Our support group members only PicoScope Users Area is the best place to go for specific PicoScope help and discussion.  So, when you have PicoScope operational questions, gripes, suggestions, or want to read and discuss different software releases, view our latest instructional videos, etc, etc..that's the place to go.   ;)

Hi George

Nice to see you are using a Pico and hope to see you around here in the future.

I have limited experience with this vehicle so take this for what it’s worth.

I'm trying to establish some reference for later. This is a new vehicle ML164 with 4 miles on the clock, I'm doing a PDI (Pre Delievery Inspection), no problem (what would you think otherwise?:-). I was told base Cam timing should be lined up. True? Or my scope setting not right?

your cams look perfect if you line them up like this picture below, can you activate the cam timing to see which way the cams move in relation to each other

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Hi George,

I can assure you there is virtually no time lag between channels. Want proof? Of course you do. Man, I feel somewhat intimidated by you being a member here. Mr. Ge, I'm honored to see you participating here. Your wealth of knowlege supersedes much of what I know. Dude, maybe you should be the Moderator! Thank you for joining us George.

How can we demonstrate the channel time lag? Well, Tom and I discussed this earlier. He and the engineers are much more in tune to this than I am, but I'll give it a shot. I put both A & B channels on an injector using the 20:1 attenuators. The sweep speed is 500uS. Here is that capture. Next, I'll zoom in on the traces by a factor of 2000.

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As you can see in this zoomed capture, there is 49 nanoseconds between channels. So, would this be a lag in Automotive service? Certainly not. It is virtually nothing. Clock speeds in picoseconds for an engineer? Perhaps, but we do not need anything that precise in our field currently. I'm not saying that it couldn't evolve to that in a hundred years, but right now, a few nanoseconds between friends is nothing. Nice to meet you in Denver by the way.  

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Hi, Tom, Mick, Carl, and All:

I appreciate you all taking time to answer my stupid question. I’m convinced the "Time Lag between Channels" is a very minor factor not only in this case, but also in my later use of PicoScope. 50nS, even with the light speed, I don’t think it can get to any star near us.:-) If you don't mind, I'll make some random comments.

Tom:

1, I really enjoy your sample rate calculation. At the same time, I was also scared and unsure about the sample rate could be the same as time lag between channels.:-) As you have stated very clearly, those are two totally different concepts. Cool!

2, Also, Tom, you brought up CKP to CMP relationship. That was the 1st thing I was heading to, but gave up, as I couldn’t clearly show the absolute CKP position without R&R transmission, I’m heading that way, thu. MB 722.9 transmission (our new 7 speed automatic) doesn’t have less trouble than those VVT.:-)

Mick:

1, Good point those intake or exhaust lined up individually. I thought so too. Then, I blew it up 50X, saw ~ 600us - 800uS between them. On that RPM, it’s ~ 1.5 deg difference CAM RPM. Then, of course, there is ~ 20 deg between intake and exhaust. Very different than what I was told by MB’s Feb 2007 Shop Foreman’s meeting notes. Without knowing the time lag between channels, it triggered my stupid question.  If I had examed a little more closely, I wouldn’t have asked in a such stupid way. My channel 1 and channel 2 had the more “time lag” than channel 1 and channel 3, I think anybody in his/her right mind would multiplex signals 1 2 3 4 other than in a random order, right?:-)

2, Mick, you mentioned VVT activation. Good call! Exactly what I did today. Once I gather enough captures, I might bring it up in the General Discussion as Tom suggested.

Carl: Yeah, Denver. It was my great honor to meet you in person, it’s like yesterday in my memory. I have to give you a little hard time here, thu.:-)

1, You said: “I feel somewhat intimidated by you being a member here.” LOL!, I laughed so hard, my wife came to check on my temperature.:-). Then you said this: “Dude, maybe you should be the Moderator!”, my wife said “ I think you can barely moderate yourself”. Actually, she really knows me, so do I. I have strong points somewhere, work a little better when I read a formula and trying to understand it, for example. But using Scope is surely my weak area. I don’t feel shameful to ask your help, Carl (as I really see you are my friend). Among lots other my bad habits, over-thinking is the worst, I know that, as I have displayed very well here. However, I feel quite at home here at Autonerdz’ compared to some other forums I have attended overseas. So, Carl, please don’t give up on me yet.:-)

2, Your experiential proof is beyond any reasonable doubt. You have clearly shown the conceptual differences of ‘Lag Time between Channels” and “Sample Rate”. Now, I can put my heart back into my chest.

Later, If I figure out how to upload Pics to here, I will bring up some case studies’ of myself, in General Discussions, of course.

Thanks to All.

GG