Firstlook sensor to measure timing.

Ask for and share advice on using the PicoScope kit to fix vehicles here.

Firstlook sensor to measure timing.

Postby heady2010 » Sun Jul 30, 2017 5:23 pm

Hi all,

Does anyone have any details of how you could carry out a timing check just using a first look sensor and not a wps?

I'm guessing a good overall view would be on a known good engine to carry out a cranking check first and have one sensor in the intake and another in the exhaust along with starter current, crank signal and cam if applicable, maybe include a maths channel on the crank signal to highlight tdc from frequency. Then make notes of where tdc occurs on the crank signal and cam and then measure the degrees to the intake and exhaust pulses, then carry out the same tests with the engine running and at different revs. Then carry out the same checks on the suspect faulty engine and compare? (This would be a petrol engine with any form of variable valve timing disabled)

If anyone has any input or pictures of waveforms that highlight how to achieve this that would be good.

Thanks
heady2010
Newbie
 
Posts: 7
Joined: Sun Feb 08, 2015 11:03 pm

Re: Firstlook sensor to measure timing.

Postby FioranoCars » Sun Jul 30, 2017 8:35 pm

Hi
I've not used mine for timing checks, but on youtube there are quite a few videos around that area, but as I have a pressure transducer not followed it up, try https://www.youtube.com/watch?v=ZzvLrAo1YVM there are others, maybe search for piezo pressure transducer too.

If you get anywhere, please do post back as I'm keen to get more use out of my firstlook.

Measuring degrees can be done using rulers, which is a built in feature, just in case you were not aware of it, covered here https://www.picoauto.com/library/training/scope-school-part-3-tips-and-tricks but lots of talk about them if you search for "rotational rulers"

What car are you planning to test? Have you looked at the waveform Library?

Not sure why changing RPM would assist you, can you enlighten me on what you hope to see ? I would personally think the lowest stable rev's would be best, as you'll have more chance of seeing the issue, under load might reveal issues not visible at idle, but that's another story. Steve Smith has identified throttle body butterfly flap (if you have one) being slightly open to help show the pressure changes, so this might be worth playing at to see what achieves best results...

Cam Phase and Crank are both good to correlate for timing, no point just doing crank.

Again not sure why rotation frequency/RPM is going to help, if you look at WPS timing analysis captures it's not critical to the valve events, unless you rotational speed is changing during the 720 cycle? Better to stabilise that, maybe at 1,000 rpm if running or using an additional battery if cranking only ?

Not quite the answer you had asked for :? so please excuse the "devils advocate" approach, but easier to challenge your thinking now, and give you some fresh ideas, than waste a shed load of time later.

You need to think through your test plan and what you expect to see, and how you can use them, yes plenty of suck it and see needed with a firstlook, but you still need a plan and to think it through or you'll not understand what you've captured ??? just my 2p

Hope that helps, and please do report back, or link to anything else you find useful, as I know a few of us here don't make full use of this tool.

Richard
User avatar
FioranoCars
TwoWaves
TwoWaves
 
Posts: 377
Joined: Thu Dec 13, 2012 1:26 pm
Location: London, UK

Re: Firstlook sensor to measure timing.

Postby heady2010 » Sun Jul 30, 2017 10:10 pm

Hi Richard,

Thanks for the reply and information. Yes as you say I would be using the degree rulers to highlight the 720 degrees of crank rotation.

I don't have a specific car that has a fault, just thinking of building a data base.

All of this of this is new to me so im probably over thinking a lot of it and most of it will be trial and error, but my thinking behind changing the rpm (by this I mean hold steady at certain rev ranges and also a WOT test) is just to test the timing under different conditions, load, temp, oil pressure, oil viscosity etc just to help see any potential issues that might arise only when tested dynamically with things like a chain, tensioner, VVT, worn keyways and worn crank. I understand that some these tests may not reveal the detail I want and as you say the clearest image will probably be at a steady idle or cranking. I will definitely have a play around with the throttle body during testing, thanks.

So my thinking here is that, taking into account one of the ways of checking valve timing is identifying the valve opening events in relation to the 2 pressure peaks that the wps provides and the 720 rulers. However, with no wps to provide the peaks to reference from, I initially would want to recreate this reference point in as many ways as I could, so the peak of a starter current hump, the crank signal slow down as it crosses the tdc peak, maybe battery voltage AC coupled then align these events then with the actual crank signal which in theory should be the same tooth you could actually look at that the sensor is picking up if you manually set the engine to tdc, and also lining it up on the camshaft signal as well. Hopefully I can then say with confidence that for example at teeth numbers 15, 30, 45 and 60 are my tdc points regardless of engine rpm within reason, from this point i could then measure the degrees to the exhaust and intake pulses providing i can get a clear consistent pulse to reference from, this should then also help reveal any cylinder specific timing issues like a worn or spun cam lobe. So by doing this will hopefully give me as much detail as possible to see how things react under load to help build a decent test and also just for curiosity.

As you say cam and crank correlation checks can be very helpful, but I'm trying to cover all bases including that a engine might not have any cam sensors at all, or only have a inlet cam sensor and the exhaust cam might be out of alignment.


Another thing I was pondering is what kind of image you might get if you took an in cylinder measurement with a first look sensor, I know the pressure may be too much for it potentially but if you had a compression hose into the cylinder you could fit an adjustable valve between the sensor and the hose which might allow you to lower the pressure to a readable level. I also understand that the sensor reacts differently to pressure changes in comparison to a wps and would probably not give you the same level of detail, but it may give you the reference cylinder peak pressure.

No need to apologise, i completely agree that we all need to be challenged! I am hopefully going to carry out these one night this week, in the meantime feel free to rip my theories apart:-)

Thanks again.
heady2010
Newbie
 
Posts: 7
Joined: Sun Feb 08, 2015 11:03 pm

Re: Firstlook sensor to measure timing.

Postby FioranoCars » Sun Jul 30, 2017 10:43 pm

Hi again
Totally cool, sounds like you've put some thought in, so go for it and share/discuss the results here, that's the whole point of the forum.

I was going to use the Firstlook as an extra aid to WPS style in-cylinder within the inlet and exhaust to study pressure waves, not helping here, but that was my next goal. Using it in cylinder will have a different set of issues, as it's not an absolute reading merely a "change", not sure you'll get anything to give total compression, especially at starter motor cranking speeds, but not tried it myself so give it a go!

Cheers
Richard
User avatar
FioranoCars
TwoWaves
TwoWaves
 
Posts: 377
Joined: Thu Dec 13, 2012 1:26 pm
Location: London, UK

Re: Firstlook sensor to measure timing.

Postby STC » Sun Jul 30, 2017 10:48 pm

Another thing I was pondering is what kind of image you might get if you took an in cylinder measurement with a first look sensor


You would get to see the Image of a Ruined First Look Sensor. If you got the pipework to seal, first the rubber hosing would balloon up and simultaneously the housing will quite likely be blown to bits - especially a diesel !!

In your desired application it would cause more problems than it would answer.

The way forward with valve timing analysis is to compare with a known good, either an engine, a previous capture, VM tech Info, Pico Library..... ....

The WPS or Equivalent (PV350) is the way forward and that still will not be as conclusive as a known good. We use pressure transducers when we don't have a known good !

I stand to be corrected but with a WPS or 3 in the armoury the First Look is redundant ?

First look will never give a pressure reading, only point out directional change. You would get more diagnostic value from scoping a Map, Maf & Exhaust pressure sensor.

Time moves on. I would like to scope a Pressure Sensing Glow Plug, Then buy and adapt one as a diagnostic tool, for engines not born with them, which does not have the 500 psi or temperature limitation. Watch this space :D
User avatar
STC
Banned
 
Posts: 790
Joined: Sun Sep 13, 2015 4:10 am

Re: Firstlook sensor to measure timing.

Postby heady2010 » Sun Jul 30, 2017 11:03 pm

That sounds like a good relationship test and would be interesting to see, I don't have a a wps, but if I did it would be good to use it on a good engine, mark the valve events in relation to the crank signal, then carry our the same tests with a FLS in inlet and or exhaust but with the wps removed to avoid any air disruption. Then line up what you know is the 100 % the valve events and see how they correlate to the FLS measurements. Feel free to do this and post it on this thread :D

Yes I agree the starter motor speed maybe an issues in it's reaction time before it defaults to it's base line.

Thanks
heady2010
Newbie
 
Posts: 7
Joined: Sun Feb 08, 2015 11:03 pm


Return to Diagnostic discussion

Who is online

Users browsing this forum: No registered users and 0 guests