Smart ForTwo | Misfire

Anonymous
April 03 2014

This is such an awesome tool,i will get one soon.This is so cool how it does all these different tests in a very short time.Thanks PICO.

Lucian
August 23 2012

Interesting, but it just goes to show how little people know about Smarts, you have diagnosed the symptom (burnt valve), but the cause will actually be sticking piston rings and therefore loss of oil control on cylinder walls! Change only the valve and you will do it again next month too.

Daniel
December 31 2010

This exemple shows different use of the scope and its accessories. In our workshop, on audible suspicion of a misfire, we will go first for the easy and quick relative compression (before looking at ignition or VE), with a pick up on cyl #1. Then check the suspected faulty cylinder with the wps500…the full compression cycle will tell the complete story. Roughly 5 mn, one technician, to fully diagnose the issue with accuracy and minimal activity. I bet my old foreman will also go for a smoke test to see the leak (he doesn’t like PC). It requires a much longer time to prepare the quote…
Then it is certainly a good practice to redo the wps500 compression test after the fix, to make sure there isn’t another hidden issue/cause and demonstrate the job performed to the customer (ours appreciate the before/after).

Aaron Firth
June 15 2010

Got to agree with how quick the relative compression tester is, whats quicker than just clamping on a battery?

Samuel Jarrvis
January 07 2010

I am somewhat surprised the Pico Diagnostic cylinder contribution software was not run first.  I have had mixed results with the cylinder contribution tests. So I can understand.

In my experience the relative compression test has been very accurate with one exception.  A bad starter one time resulted in an inaccurate test result.

Something I believe most people do not realize is the Pico Diagnostic relative compression test uses only the battery connection.  Most times a high current inductive amp probe is required. This I believe is due to the high resolution of the 3000 and 4000 series scopes.  It is possible to record DC voltage then zoom it times 50 and see the swings as if it were AC coupled.

A couple of thoughts on the captures. It is possible to utilize the second channel to display other measurements.  Since this was a bit of play and test it would have been interesting to show either the first look or a pulse type sensor displaying that on ch B and showing the graph or jump the WPS to ch B and display the compression waveforms.  Even a current probe on ch B could have been cool.

While a mechanical compression gauge has its place there is a lot that can be seen using compression waveforms and intake and pressure pulses.

Overall I find the relative compression test my most used Pico Diagnostic (software).  It is super quick to use with one connection to the battery for a quick go/ no go on engine mechanical.  Sure if I hear an engine cranking unevenly I will dig further for a mechanical issue.  It also builds value for me and the shop.  I can print a professional looking report showing test results.

Samuel Jarvis

Dave F
November 25 2009

Hi

The design of modern engines is changing, I suppose in a way catching up with the boom in electronics. 
We have multi valve, VVT, variable valve lift, variable intake etc which all affect engine breathing. As others have said, access to spark plugs on some of these units to do what were once quick tests can present quite a challenge.  The use of pressure transducers which can monitor mechanical events ( intake, compression and exhaust ) can offer a great deal of non invasive diagnostic information in a short space of time. 

I didn’t read this article and think about how much quicker I could have done it with a compression gauge, I was thinking about how investing in methods and equipment like this will improve efficiency and accuracy on the more complicated engines to come. This example by Pico is only a simple demonstration of one basic application for their pressure transducer.
For me it’s about learning on the simple stuff then you know what you’re looking at when it matters !

Just my thoughts

Dave Foye

Michael
November 24 2009

Yes i think this test has its place as jez has said on a V6 Freelander the rear spark plugs are under the variable intake part of the manifold, & this would be a far more cost effective & quick test.

jez
November 23 2009

Imagine this was a V6 or something! far quicker using the Pico than a compression tester. I reckon you could diagnose a major engine fault within 5 minutes, how long would it take to remove each plug etc etc?

Matt Williams
November 21 2009

Firstly I would like to thank all for taking the time to leave a comment on this article.

Unfortunately I think a few are missing the intended point, that being to show a usage of our product.  It is of course true to say the issues with this particular vehicle could have been diagnosed via other means.  However I am sure some have realised that in using our equipment the problem can be recorded, thus evidence can be given to prove the need for a rebuild.

Also good news for those interested in the pressure sensor it is now available!

Tom
November 20 2009

Far to complicated simple method remove plug realise something wrong compression test

Ken
November 04 2009

Sure, tease me with the pressure transducer that I cannot yet purchse. LOL !!

Les Miles
October 26 2009

You may have fun playing around with your own car but for a customer I would have done several quick things. 1 listen at the exhaust(so simple) 2.compression gauge would have told all the story 3.needle bounce at the manifold suction test.
Here I say have fun if you have nothing better to do by all means but not at the exspense of the poor motorist—go and refresh your basics

Sergio
October 26 2009

Thanks for the teaching on this, i think you could find this problem with basic tools faster and easier like a vacuum gauge then spot the bad cylinder. The burn valve was because of the valve not seating because of excessive carbon built in the valve seat or exhaust leak.

Mike
October 24 2009

Ah, in the old days you would have run the engine and removed and then replaced each plug cap in turn. This would have identified the cylinder. Removed the spark plug to check for good spark and found the spark plug burnt indicating too lean a burn. Removed plug leads from other cylinders, put thumb over plug hole and brief crank of engine would have found the lack of compression. I am not knocking an excellent product or manufacturer, I use their products daily but if a motor mechanic needs to go to this length then he/she will definitely miss the cause of the problem and simply replace parts and reassemble.
As to the cause, thats where Pico do come into their own.

andrej
October 24 2009

To diagnose a failure to bring equipment worth thousands of dollars is not necessary. Suffice kompresometr for $ 40

Rick
October 24 2009

Although I love my Pico wouldn’t a compression gauge found the same fault? Its time and money while I happen to have a Pico scope lets always complete the testing with the fastest and cheapest equipment/ For us and the customer. Driving a Smart is all about keeping the cost of ownership down.  Thank for a great article I did enjoy it especially since I also own a Smart.

Simonsse
October 23 2009

Although not in the motor industry, I follow these articles with great interest.  This particular one would benefit from more detail.  How was the ignition system checked, how does the cranking current derived pressure test work, and how about some captions on the photos.  Great series though, love them.  [Also makes me wonder about reliability of highly stressed small engines.]

Dave Baxter
October 23 2009

And that “suddenly” happened?

I’d suspect something else caused that valve to burn, especialy if it did indeed do all that damage in only “one mile”...

The battery voltage/cranking current compression test, is a new twist on an old exprienced machanics ear.  Likewise, I suspect the engine exhibited symptoms an experianced ear (or sympathetic drivers ear) would have detected, prior to the terminal valve burn.  Was the valve seat damaged in any way?  How about the fuel injector for that cylinder?

All good fun.

DJB