Diagnostics using Pressure Transducers

Hello Everyone,
I've been working in the auto industry longer than I care to think about, and I'm the one doing all the diagnostics in our shop. I've been following the use of Pressure transducers to help diagnose since it came on the scene. I must say that I've been rather skeptical, and have yet to jump on the band wagon. I just took a two day refresher course, and the instructor was giving pressure transducers the big thumbs up.

I'm looking for some more insight. Is it just a good way to prove what you already know? Or can you really use it to help diagose cars? I see many posts where people are disabling a cylinder to show the changes in waveform generated. I keep thinking it is much easier to make observations when you already know where the problem lies. Can you really glean usable insight when the problem is not already known?

I just got access to a FirstLook for an extended period of time to play with. I know I can't directly connect to a cylinder, but I'm hoping connecting to the exhaust, and intake will give me an idea if this can really be used to help in Diagnostics. I would love to be able to get a glimpse into the mechanics of the engine without having to start pulling things apart. I've seen quite a few engines where a compression test looks good. But when we did a leak down test we end up finding a bad valve. And sometimes even that isn't enough. A broken valve spring might not be shown with that test either. It would only be us knowing that a problem existed in that cylinder, and doing a tear down that we would find things like the valve spring, or worn cam lobe, etc,.. Can you really see these things with pressure transducers?

I'm going to give it a try for a while, but really just wondered what others thought.

Thanks,

Marcello

Hello Marcello and thank you for your detailed post.

In my opinion the pressure transducer has become as essential as a current clamp.

There may be some scepticism surrounding that comment given I work for Pico, but rest assured, from the work I have carried out with the WPS500 I can safely say I would have been lost without it.

Regarding “looking for more insight”, I am sure you have seen the case studies and watched the tutorials from your comments and the time you have spent with this post.

All I can do is share my experience with the device here and I would love others to do the same.

From a non-intrusive approach to diagnosis, the pressure transducer can provide critical pointers when evaluating intake, exhaust, and crankcase pressures/pulsations in a relatively short space of time. When you add in an ignition or injection event to your pressure waveform you can go onto identify offending cylinders with no dismantling required.

The key is evaluating what you can see in relation to other cylinders (using sync).

By disconnecting injectors and introducing air leaks etc. will assist with evaluating the effects of such intrusion, separating cause and effect.

I agree totally with your comment “I keep thinking it is much easier to make observations when you already know where the problem lies” but you can flip this around as part of the never ending learning process.

Hind sight is a powerful learning tool and I myself have not fully understood how a component has rectified a concern until I have looked back over the evidence gathered.

Reviewing waveforms before and after fix requires analysis time, but the answers are there along with the “lesson learned” ensuring you are armed and ready to resolve the next diagnostic challenge.

Using the First look sensor is going to give you an excellent insight into the efficient running of the engine and must never be discarded as an essential diagnostic tool to accompany the WPS500.

Having both devices is going to give you excellent “one hit” coverage when looking at the relationship between exhaust gas pulses and in-cylinder pressures under fault conditions, and here is where the WPS comes into its own.

With an in-cylinder waveform capture you will be able to evaluate valve timing, valve open and close events, compression loss, exhaust back pressure, intake restrictions, and peak compression via one connection to your scope to assist you with “a glimpse into the mechanics of the engine without having to start pulling things apart”.

Once again analysis is key, capturing waveforms from suspect cylinders and comparing against known good cylinders will reveal issues surrounding poorly seated valves, broken valve springs and lobe wear etc.

The WPS500 can also be used for fluid pressure measurements (static and dynamic) adding additional tests to engine running evaluation with regards to fuel pressures as just one example

I hope some of this information is of value to Marcello and others alike?

Take care……Steve

Steve,
Thank you for your reply. After going back and rereading my own post I want to make it clear that I believe the WPS500 to be truly useful tool. I was truly amazed by the information that could be quickly and easily sampled. I wish we had them when I was in automotive school. I believe there is much to be learned from using pressure sensors.
I would just like to hear what other mechanics think of using them in everyday diagnostics. I truly hope some others will chime in. I need to come up with some kind of justification in spending almost as much as my 4423 cost me to have one. I'm hoping to make a case to the the boss, and let the shop buy it.

Thanks,

Marcello

steve smith wrote:Hello Marcello and thank you for your detailed post.

In my opinion the pressure transducer has become as essential as a current clamp.

There may be some scepticism surrounding that comment given I work for Pico, but rest assured, from the work I have carried out with the WPS500 I can safely say I would have been lost without it.

Regarding “looking for more insight”, I am sure you have seen the case studies and watched the tutorials from your comments and the time you have spent with this post.

All I can do is share my experience with the device here and I would love others to do the same.

From a non-intrusive approach to diagnosis, the pressure transducer can provide critical pointers when evaluating intake, exhaust, and crankcase pressures/pulsations in a relatively short space of time. When you add in an ignition or injection event to your pressure waveform you can go onto identify offending cylinders with no dismantling required.

The key is evaluating what you can see in relation to other cylinders (using sync).

By disconnecting injectors and introducing air leaks etc. will assist with evaluating the effects of such intrusion, separating cause and effect.

I agree totally with your comment “I keep thinking it is much easier to make observations when you already know where the problem lies” but you can flip this around as part of the never ending learning process.

Hind sight is a powerful learning tool and I myself have not fully understood how a component has rectified a concern until I have looked back over the evidence gathered.

Reviewing waveforms before and after fix requires analysis time, but the answers are there along with the “lesson learned” ensuring you are armed and ready to resolve the next diagnostic challenge.

Using the First look sensor is going to give you an excellent insight into the efficient running of the engine and must never be discarded as an essential diagnostic tool to accompany the WPS500.

Having both devices is going to give you excellent “one hit” coverage when looking at the relationship between exhaust gas pulses and in-cylinder pressures under fault conditions, and here is where the WPS comes into its own.

With an in-cylinder waveform capture you will be able to evaluate valve timing, valve open and close events, compression loss, exhaust back pressure, intake restrictions, and peak compression via one connection to your scope to assist you with “a glimpse into the mechanics of the engine without having to start pulling things apart”.

Once again analysis is key, capturing waveforms from suspect cylinders and comparing against known good cylinders will reveal issues surrounding poorly seated valves, broken valve springs and lobe wear etc.

The WPS500 can also be used for fluid pressure measurements (static and dynamic) adding additional tests to engine running evaluation with regards to fuel pressures as just one example

I hope some of this information is of value to Marcello and others alike?

Take care……Steve

Hello Steve and everybody who likes diagnostics

You have offerred a good argument, I already have a PicoScope advanced kit and very happy with it for diagnose electrical issues, now my question is: It would be helpful in any way to complement the standard AC pressure gauges with the WPS500 to diagnose Air conditioning systems, I mean we as automotive technicians already know how to compare high-low pressures, superheat and subcooling among other techniques, but as long as we have more and more information about systems performance the more we'll be able to have a better insight

Best regards
Dario

Thank you for the feedback Dario.

You have hit on an interesting point here regarding the revelations made when using the WPS pressure transducer.

Whilst you are right that for years we have used gauges for Compression, AC, Vacuum, Pressure, etc. etc. we have never had the intricate detail revealed when using the WPS.

I refer here to the in-cylinder waveform using a WPS compared to a conventional compression tester which now reveals the 4 stroke cycle events (Conventional compression tester reveals peak pressure only)

Moving onto intake manifold pressure waveforms compared to a vacuum gauge, we can see the operation of the valve train and the effects of misfires upon manifold pressure thanks to the resolution of the scope and the response time of the WPS.

The WPS is one of those tools becomes ever more useful as we apply new techniques and adaptors to justify a purchase

I hope this helps, take care.......Steve

steve smith wrote:Thank you for the feedback Dario.

You have hit on an interesting point here regarding the revelations made when using the WPS pressure transducer.

Whilst you are right that for years we have used gauges for Compression, AC, Vacuum, Pressure, etc. etc. we have never had the intricate detail revealed when using the WPS.

I refer here to the in-cylinder waveform using a WPS compared to a conventional compression tester which now reveals the 4 stroke cycle events (Conventional compression tester reveals peak pressure only)

Moving onto intake manifold pressure waveforms compared to a vacuum gauge, we can see the operation of the valve train and the effects of misfires upon manifold pressure thanks to the resolution of the scope and the response time of the WPS.

The WPS is one of those tools becomes ever more useful as we apply new techniques and adaptors to justify a purchase

I hope this helps, take care.......Steve

Hi Steve and everybody

Yes, you are correct. As technicians we have to be curious and try another possibilities. As a matter of fact I don't have yet a WPS but I will.
As for experiments I have a DIY pressure sensor which I hooked up to my pico and is sensitive enough to respond to the subtle changes in the fuel pressure regulator diaphragm. It is a GM Fuel Tank Pressure Sensor and I took this idea from YouTube, my next step is try to create a custom probe on Picoscope 6 and keep learning. I think I will need a pressure-voltage chart to do it, I am not positive about that.

Best regards
Dario

P.S.: I tryed to upload a photo but it wasn't allowed, I will try later

Thank you for the feedback Dario.

I have seen various "home made" pressure sensors, some of which were fine with good response and others that were quite scary!

The accuracy is all important when looking at pressure values, but for transitions in pressure, response time is critical.

Those I have seen and compared have all presented anomalies that the user has learned to live with and expect, which is fine for the original user but not sure this is such a god idea when it comes to sharing waveforms with others.

Regarding the custom probe settings, you could use the values specified by GM in relation to pressure/voltage and then incorporate these into your probe settings.

It would be good to draw some comparisons on the finished article.

Take care.......Steve

Either I'm doing something wrong or the forum is not accepting uploads at the moment. So I will try and share via google drive.
I wanted to share two waveform captures. 1st being a 2014 Ford Fusion inline 4 cylinder, and the second a 1993 Pontiac Bonneville v6.

https://drive.google.com/file/d/0B7XznVsF_XxtUEJ0MGxxbHFkZHNOZ081U0V1bC0yQWQ4bmhV/edit?usp=sharing

I've been making recordings of everything I can with the Firstlook sensor. I was rather excited when I sampled the Ford Fusion. It had this very nice simple signal. You could see a nice repeatable signal for each cylinder. I killed a cylinder and it was very obvious in the wave pattern. The 6 cyl. Pontiac on the other hand was very hard to look at.

Does anyone have any insight into deciphering these waveforms? How best to go about dissecting the waveform. Both signals were taking at idle with firstlook in the tailpipe and an injector used for sync.

I was thinking if every car was like the Ford this would be a breeze. I could find reproducible data with easy. Then I look at a car like the Pontiac and I'm thinking maybe not.

hb43

it happened to me the other day trying to post a sample waveform for another member, so I gave it up as a bad job.

Hello Marcello and thank you for the feedback. Martyn has sent you a reply to the feedback you have provided regarding errors when uploading to the forum, I hope this helps?

Moving onto exhaust gas pulsations, I have to say I am with you when it comes to deciphering what is happening and when.

I have managed to download the Pontiac waveform and can see the concerns you have raised.

I have been looking at the “First Look” sensor booklet which contains some valuable theories about intake and exhaust pulsations http://www.picotech.com/document/pdf/firstlookusersmanualv3.pdf along with the complexities that would appear to arise with an increase in cylinder counts and configuration.

Can you post or share the Ford Fusion waveform as this will assist with evaluation for my own knowledge base?

One "given" has to be the change in exhaust gas pulsation dynamics with "V" configuration engines and exhaust systems. The manual above refers to tuned exhausts and how these can effect the final pattern, but throw into the mix variable valve timing and overlaps and the complexities increase further still.

I have attached my interpretation of the events within the exhaust system of a straight 4 cylinder engine which is far easier than looking at a "V" configuration. There appears to be characteristic troughs in the waveform that I hope I can attribute to valve overlap, but I need more experience and time to confirm these events.



Back to back comparisons are invaluable and its great you appear to be testing/sampling various vehicles (especially those without running issues).

Once armed with known good waveforms accompanied with the experience of characteristics within exhaust gas pulsations we can then proceed with confidence.

Any feedback you have would be great and if your psdata files will upload that would be most helpful.

Take care......Steve