 | Home > Technical > Vcv valve traces.. |
 
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497  
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After playing with the injectors and establishing they were piezo operated I wanted to have a look at the much mentioned vcv valve..
My reading on here suggests that the 2.2tdci engine isn't as prone to problems with it as the 2.4 but I took a look anyway.. After a bit probing I got that it was a duty cycled or pwm operated valve but at idle and putting on a few revs it was impossible to see any real change to the cycle.. I'm guessing I will need to be able to see it under load conditions to notice the difference.. At least I know, the signal wire now and I'll get a remote lead into the cab at some point and try again.. Best I could do today was alter the time base to view one cycle and watch the difference between idle and revving the engine.. The difference in the square wave or duty cycle alters by about 154 micro seconds I think it was..  Click image to enlarge Click image to enlarge Eventually I'm hoping to be able to look at the vcv valve against the rail pressure.. |
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24th Apr 2024 4:20pm |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3403  
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All very interesting
I think you mean milliseconds ms rather than microseconds μs. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing 2012 90 CSW, 2.2TDCI, Santorini Black |
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24th Apr 2024 4:48pm |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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That's what I'm on about.. Getting a lead into the cab that has been tapped off the signal wire and has a connector for the scope.. I already have multiple leads of various sensors in the cab that allows connection of the scope while driving.. The length of the leads isn't an issue for the signal.. Many automotive scope leads are 3meters and can be extended.. As long as you don't pick up a load of electro magnetic interference it's fine👍 |
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24th Apr 2024 4:55pm |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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No.. The width of the section of the square wave when it drops from 15.6v down to zero volts is 0.446 mili seconds at idle On the second trace when reved that portion of the pulse drops to 0.292 mili seconds A difference of 0.154mili seconds or 154micro seconds👍 |
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24th Apr 2024 5:15pm |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3403
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Ahh right
I need specs  The one that sits on the nose, not numbers  1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black |
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24th Apr 2024 6:51pm |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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I'm still mucking around with the scope and the vcv valve among other things😂
Recently had a fair bit stripped out to replace glow plugs and it allowed me to take a tap off the vcv valve connector to make it more easily accessible for scope connections, so today I tried a little drive to obtain a trace of the vcv valve(in blue) the rail pressure (in red) and a line in green to show how the duty cycle of the vcv trace in blue changes as you drive.. Its all a bit squashed and as the time scale used to allow a short drive it's impossible to make anything out on the blue vcv valve trace, but I think it does show that the vcv duty cycle in green more or less mimics the rail pressure in red as demand alters.. I was surprised that the percentage change in the dirty cycle of the vcv valve is only about 10% from tick over to relatively high demand on the accelerator.. Click image to enlarge |
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12th Jul 2024 7:47pm |
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| MK Member Since: 28 Aug 2008 Location: Santiago Posts: 2408  
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Curious about ckp-injections-rpm
 Puma 110" SW
............................................................. Earth first. Other planets later |
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12th Jul 2024 9:12pm |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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Strange you should mention that🤣 but I only have a 2 channel scope and I was keen to know where firing actually took place relative to the crankshaft signal..
I looked at crank and cam together.. Click image to enlarge Then crank and no1injectot firing Click image to enlarge But you need to know on which revolution of the crank that takes place.. So a look at the camshaft signal relative to the same cyl firing.. Click image to enlarge Then using rulers it's possible to place the firing position on to the original crankshaft, camshaft trace👍.. Ie where the first verticle dotted line appears on this one Click image to enlarge If you had say a 4channel scope you could just have laid the injector trace on the same trace without all the fuss👍🤣 Do you have a scope? I bang on about it a lot I know but it doesn't appear that many people bother with them, yet along with a scan tool I would think they are most probably essential with today's motors.. I know half the issue is knowing what you are looking at and interpreting it, and that's an issue for me, as it's only a hobby, and obtaining information you need isn't always easy, but I still think it's worth the bother👍 |
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13th Jul 2024 5:13am |
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| DAZ110 Member Since: 06 Dec 2007 Location: East Sussex Posts: 2034 
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All like rocket science to me!
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13th Jul 2024 8:53am |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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Your IT skills can't be worse than mine.. And I'm not saying I understand everything, or don't get frustrated but if you enjoy messing with motors it's just something else to entertain👍.. And may even be useful if you get issues🤔👍😂
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13th Jul 2024 9:24am |
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| Bluest Member Since: 23 Apr 2016 Location: Lancashire Posts: 4194 
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This is interesting stuff even if I don't know much about electronics. I'll show up my ignorance with this.... would it be possible/practical to tap off all the sensors to a single place in the vehicle into say a big multiway plug and then somehow plug that into a scope (not sure how you'd manage switching the channels), or maybe plug into a laptop with some software to make it into a scope? Sort of like an advanced level OBD reader. 2007 110 TDCi Station Wagon XS
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13th Jul 2024 9:49am |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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What's daft about that?? It's more or less what I've done with a number of engine sensors.. I've run about 10 into the battery compartment under the passenger seat, and it allows quick easy access, but I did it just to make connecting to sensors easier..and help with the learning experience using a scope.. The issue is where do you stop 😂.. I was thinking I might run a couple more wires in but just have them so you can connect say a backprobing tool to whatever you need to look at, the relevant sensor /actuator at the time... It does allow easier scoping when driving in a lot of cases.. Some probes like current clamps are not going to be left connected anyway..
Remember what you are suggesting is already available.. Any good scan tool will give live data readout by plugging into the diagnostic socket.. And you can see what's going on..all be it not with the same detail as a scope.. But generally good enough.. |
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13th Jul 2024 10:22am |
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| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 497
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Picture of the connectors I've run in to under the passenger seat for easy access for scope connection👍
Click image to enlarge |
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13th Jul 2024 11:42am |
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| MK Member Since: 28 Aug 2008 Location: Santiago Posts: 2408
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Cool!
Not sure but I think a bit caution is needed when using a scope as wrong connections can blow the thing. Your scope is just excellent. I am keen on getting some scope hopefully soon. Thanks for the shots. Puma 110" SW ............................................................. Earth first. Other planets later |
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13th Jul 2024 1:04pm |
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