Cam & Crank Waveform Reference
Good morning all. Hope this finds everyone well in these chaotic & uncertain times. I was curious to know if anybody has information regarding what the reference notches on the cam & crank waveforms for this engine indicate. The service manual I have doesn't specifically say whether the missing crank teeth indicate slightly before TDC for #1 & #6, nor does it discuss what the reference pulse from cam signal denotes. This is a known good waveform from a running engine. Incidentally, the truck wouldn't start while I was hooked up to the crank sensor circuit, I assume due to the bias voltage the ATS scope runs to check for connection integrity. Thanks for any and all input here.
My understanding on diesels is the missing teeth have no real correlation with TDC. Say if you were doing a relative comprssion test you'd first have to see the injector firing vs crank correlation. Then disable injectors and use your first waveform for cylinder identification.
Brian that's interesting to note. I was at a scope class recently and we were discussing the fact that you never know what the unique identifier in cam and crank waveforms correspond to. You'd think TDC for #1 but there's no guarantee. Just to make sure I'm understanding you correctly, you're suggesting to run the engine while scoping cam, crank, and let's say an injector current pattern to…
Correct. Or even just cranking while graphing the 3, so long as the injector fires. Then using that as reference you can identify your problem cylinder in your RC test.
If you related an in-cylinder pressure waveform (or an relative compression event) to the ckp/cmp signature you can work out the reluctor's missing tooth with regards to TDC.
Jurgen that's exactly the reason I ask. I do have a relative compression capture with both of these signals and I'm trying to determine which cylinder is low. I can post that as well.
Post the captures.... Another option but more messy is the following: As the injector will spray just before TDC compression in a Diesel engine you can disable the high pressure pump and (supposing it's a common rail you're working on) feed a voltage for the railpressure to the edc. This way the edc will still fire the injectors but the engine won't start
Here's the relative compression capture. I took this one using the voltage drop method so the smallest voltage drop is the low cylinder. Had to smooth it out a bit too to clean up the hash. The current waveform was better defined but you couldn't make out the cam & crank signals very well. One of the few thinks I don't like about the EScope is the fact you can't have different scales for…
Disabling the injection and simulating a pressure signal is a way to go. It might be even easier just to pull a glow plug out and take this cylinder as reference during another relative compression test. You still could relate this waveform then to the ckp/cmp signals if you wanted.
Jurgen I somehow missed this response when you posted it Friday. Pulling a glow plug is a great idea too. I've done a similar thing on gas engines with a spark plug when there wasn't another good place to reference or trigger from. Thanks!
Hi Zachary, if you have a BIN file with the current waveform and would like to rescale it, could you post it as an attachment?
Dmitriy, I have a REC file with that information & can try to rescale it. Ever since the last update on the EScope software, it seems deep record files have changed from BIN to that format. I've yet to find a way to have multiple y scales on the EScope platform like you can with the Pico. It's one of the few things I don't care for. It did occur to me after the fact that I may have been…
Zachary, a REC file would be just fine — I will rescale the data inside for you and post the result.
That's awesome Dmitry! Thanks for that! I'd love to know what your using in order to rescale if you're willing to share it. No worries either way. I'm away from my laptop this weekend but I'll post tomorrow evening or Monday morning.
Dmitriy - Here's a BIN version of the current waveform capture for rescale. It wouldn't let me upload the REC version. Thanks again for your help!
Does this look OK? If yes, I will export the matching BIN file. diag.net/file/f1y0k5fi5…
Dmitriy that looks great! Thanks so much for doing that.
Zach- I dont have your answer,but am intrigued by the bias voltage issue. If the bias voltage is indeed keeping your vehicle from starting,I have to assume it is also disrupting your crank sensor wave form and that doesn't appear to be the case in your picture. (well that is to say your capture looks clean,I dont know what good looks like on this vehicle)
Rudy I thought it was strange also. I don't know for sure that I'm right about that but I believe this system uses a 2.5 Volt bias to detect for circuit opens. I do know that it wouldn't start with the scope hooked to the crank sensor circuit and the ECM set a code for a noisey crank signal. Ever now and again it would cough like it wanted to start but never would. As soon as I disconnected from…
Hi Zach, does the escope have floating or common grounds? Were you scoping the camshaft signal at the same time as the crank when the vehicle was a no start?
Hi Carl, The Escope uses a common ground & the leads have the ability to hook up to both sides for pm sensor or ECOP connection. I was hooked up to the cam sensor as well when it wouldn't start. It would start when I was only hooked up to the cam but not the crank sensor. Thanks for your response!
Zachary how did you make your scope connections exactly? The Escope uses a common ground for all channels. It sounds like to me you created a ground loop which shorted out your sensors. Next time when you do crank and cam only sample one leg on each sensor. As for knowing where no 1 is exactly on your vehicle I always look at Injector current with crank and cam and then I use frequency plot off…
I was thinking along the same lines Michael, would it be correct to say that if you were to connect across the Ckp using both pins you would effectively introduce AC voltage to all channel grounds?. If so I imagine that could cause some funny issues.
That makes sense to me Carl. It seems so obvious now that we're chatting about it. I was making the assumption that I needed to be on both sides because these sensors don't have a dedicated signal wire. Sounds like that only applies for a floating ground setup. One of the many things I appreciate and value about this forum. So many smart folks here willing to share their knowledge with each…
No problem at all, we are all here to help and learn. It is a great resource and I have learned a ton since reading this place page to page! I often search for a topic I am currently looking into and sure enough someone has talked about it on a level that far exceeds my understanding but that is how I learn.
If introducing ac-voltage from the ckp affecting the ground circuit of the cmp shouldn't this result in a "floating"cmp signal accordingly to the changing ground reference from the injected ac-voltage?
It's not so much about the introduction of ac voltage Carl its because your creating a path to ground, thats why the truck wouldn't start. The sensor can't send the signal to the ecm if its grounded. Make sense? This gives me another video idea.�
Absolutely Michael thanks. Look forward to the video.
Zach, Just a FYI on the escope leads. The extra ground lead is mainly for attaching accessories like amp clamps that use banana jack connections. For most situations the extra ground is not needed.
Bob thank you for that feedback. I knew it was needed for the ECOP probes but didn't realize it was only for add ons I'm general. I'd been assuming up to this point I needed both parts hooked up with an AC circuit because of the lack of chassis ground. Similar to if you were sticking a voltmeter on the sensor but I guess that's really just a floating ground anyway. Thanks so much for your input!
Just unplug the injector harness and connect one lead to an injector control wire for a sync for the RC test. Should be easy!?
If that works great but I bet the computer will log a code and shut the drivers down. At least that is what happens on Cummins. I hook up a injector that I have taken out of the cylinder if I go in cylinder.
Good point Michael. Could also substitute a load with big bulb or something and try that. Are these conventional solenoid or piezo injectors? Probably not just 12 volt control ??
They are a solenoid type with 2 wires and they put out 50 Volts to fire on the common rail systems.
A resistance measurement will show which type of injector he's dealing with. A "regular" injector, although triggered by a capacitor, will show a very low resistance, typically 0.3 to 0.t ohms, piezo-electric ones are practically open circuit and will show very high resistance of at least 100 Kohm.
That is for Cummins by the way. On Zachary's Engine I don't know.
A couple thoughts on that idea Caleb. First, there is no need to unplug the injector to get a trigger signal off of it. Second, if you're trying to sync timing events you are better off with an ignition sync. The ignition timing is more consistent whereas injector timing can vary pretty significantly. Update: Caleb, I didn't realize you were working on a diesel so obviously ignition sync is…
My understanding is that he's working on a diesel engine. So he is almost obliged to sync from the injector pulse. But to get a relative compression waveform he has inhibit injection..... So this is where it may come in handy to disconnect the injectors and use substitute loads if the edc unit wouldn't pulse while the injector circuits are open are disconnected/disconneced.
Good evening all - Just got back into the loop and saw I had several responses. Going to try and adress all of them with one response. Caleb - Michael is absolutely right. This system will flag circuit codes for the injectors the moment any are unplugged and not fire them. These are 4 wire dual solenoid HEUI injectors much like the ones in a 6.0L Powerstroke or VT365 International (same engine…
Please try to open the attached BIN file. newCh1 := 0.01*Ch1 newCh2 := Ch2 + 4 newCh3 := Ch3 newCh4 := Ch4
Dmitriy the rescaled file worked great! Thanks so much again for doing that.
Glad to hear that. I’ll describe how to do this transformation in a separate post.
Back on this truck yesterday afternoon & was able to get some better captures. Interestingly enough, the cam signal isn't as clean when hooking to just one side of it. I was able to unplug the ICP sensor & substitute my load box for the IPR to trick the computer into firing the injectors. That made it possible to reference #1. The current clamp was around the power supply wire to the…