We have taken the most popular case study from our Picogroup area and made a movie out of it.

This is a 2003 vehicle with an unsolved problem since day one.  It had made the rounds up and down the West coast where many technicians tried but failed to solve it.  

The buck was stopped with a PicoScope.   ;)

Enjoy:

http://www.autonerdz.com/flash/wranglerfromhell.html

awsome; thanks (x2) for taking the time to present case study, its always better when theres a movie,  gives it a classroom (shoptime) feel,................................................you have 45 psi when the problem occurs, if i were to see this i would have said good(without all the time on screen to compair), i mean 45 psi on alot of cars is good for running compression, i would have thought that the 45 would be enough to compress and breakdown the molecules of fuel for combustion, the main problem would be that the better part of the mixture would be going out tail pipe before spark ignites it? i would have figured it would have shown on the intake valve opening vacuum of the compression waveform, this kind of stuff is tricky, was there anykind of lifter noise?   im not that familiar with gas but on that same token if you were to make it richer would it quit missing?

Thanks, Brandon.

There was no lifter noise.  It was tight not loose...until we placed the washers under the rocker stands   ;)

The lack of compression does not explain the misfire completely.  There were other factors.  The wind over the spark plug as the compression rushed out the exhaust valve as well as the possible induction of exhaust gasses into the cylinder, diluting the mixture.  Just theory.... :-?

We did induce some added fuel just for kicks during the misfire and it had no effect.

Great case study and presentation Brian & Tom.

Thanks!

Do you have any prerelease info on the transducer adapter?

Thanks,

dave

Emailed you that stuff, Dave.  Hoping to have something more this time next month.   ;)

Yes, thanks for this presentation Tom.

Tom Roberts wrote on Jun 19^th, 2009 at 9:57am:

The lack of compression does not explain the misfire completely.  There were other factors.  The wind over the spark plug as the compression rushed out the exhaust valve as well as the possible induction of exhaust gasses into the cylinder, diluting the mixture.  Just theory.... :-? We did induce some added fuel just for kicks during the misfire and it had no effect.

Since it was an exhaust valve hanging open, I would think some of the explosive force of the power stoke would be diverted out the exhaust too. This won't show on the pressure capture as that cyl. is not firing with a pressure transducer hooked to it, but it's probably what effected the fuel trims some. I would like to have seen if the trims settle back near zero after the lifters were replaced. It might also be a good idea to run a video scope in the cyl. just to make sure the valve hasn't burnt any and the seat still looks good.

Very good movie that really shows the power of the new 4000 series PICOs. I don't need a scope everyday, but when I do it's good to know that it's not one that's going to be holding me back. Even though OEM scan tools are getting better everyday, a good scope still comes in handy to find those rare problems that always seem to find there way to my bay, not to mention that it's one of the most powerful diagnostic tools that's not OEM specific.

It's sad that the owner had to live with the problem from day one with many visits to the shop. A lemon law could have been put to use on their part if the Dealer's couldn't correct the problem after many visits. Just think of the premature damage done to the Catalyst over the years. Anyway, I bet they're happy none-the-less to have the problem finally fixed and grateful that it ended up in the hands of someone who could trace it down (not just the simple stuff).

Thanks for the presentation Tom and Brian,

Im going to dig deep into my wallet to buy me the new PICO . . . absolutely powerful.


P.S.  Keep me posted on the new transducer kit as well.

Thanks

        Rafael

James,

The fuel trims didn't change much with the misfire present and when it was not.  Much more detail on that in the full discussion thread in the Picogroup area.  Perhaps it had to do with the fact that the event was over about the time the T-stat opened.


Quote:

It might also be a good idea to run a video scope in the cyl. just to make sure the valve hasn't burnt any and the seat still looks good.

I'm confident this was covered, as the head had to come off again to change the lifter.  


Quote:

It's sad that the owner had to live with the problem from day one with many visits to the shop.

The dealer owned this one.   ;D  Used car dept.  I think it's been sold now and is on the road again doing what it was made for.  It has been passed around all up and down the coast.  The buck stopped with the PicoScope.   8-)

Rafael,


Quote:

Keep me posted on the new transducer kit as well.

Thanks,

We will announce it on the forums when we are ready.  

Thanks Tom and Brian for putting together the movie to follow the details of how you did the troubleshooting on this vehicle. It was easy to follow your progress to determine what the problem was. Thanks again for taking the time to share this with all of us.

Terry

tom,
can we download your movie to keep for ourselves?  if so, how?  i tried, but can only see it when connected to the internet.

great movie, by the way!  some of what i saw on the compression waveform (when misfiring) doesn't seem to match up to what i've learned about tight exhaust valves, but that just makes it more interesting.
thanks.

Quote:

can we download your movie to keep for ourselves?

Sorry, no.  This Flash format is designed for web viewing.

Glad you enjoyed the movie.  Feel free to share the link with others.   :)

Just watched the film and just wanted to say -- Excellent!
A good display of diagnosis without striiping the engine to pieces, as some other service agents had done.
Someone obviously missed that cam sensor as well.

Quote:

Just watched the film and just wanted to say -- Excellent!

Glad you enjoyed it.  Thanks for watching   ;)


Quote:

Someone obviously missed that cam sensor as well.

That issue was quite recent and solved easily.  Interesting that the list of possibilities for those codes in the factory information did not include the cause.  Kinda like an ASE question...the real answer was none of the above  :P  

The cam sensor issue was just a distraction on top of the #6 misfire problem.  Kinda have to attack multiple problem vehicles by clearing the obvious problems one at a time and see what's left.

Great Diagnosis and process of locating a tricky fault. Always a nice feeling of satisfaction solving a problem that got the big shop boys beat! Anyway this question is probably a technical language issue as im from the uk, but can you explain how you done the running compression test with a transuducer? Many Thanks please post more movies like this they are very educational,informative and make the public realiize just how complex the systems are under the hood.

Quote:

but can you explain how you done the running compression test with a transuducer?

First, the spark plug is removed and an open compression hose is put in its place.  Then the pressure transducer is attached.  This device converts the pressures into voltages that can be displayed on the scope.  PicoScope also allows you to configure a custom probe so that these voltages are displayed in a pressure scale of your choice.

Wow, what a great video! :), It really shows the in and out of the whole diagnostic process  [and probably some dead ends too :-[]  Awesome.
Can the 3400 series catch this running comp. test for 8 minutes :-?

cheers Mark

Thank you, Mark.  Glad you enjoyed it.   :)

Yes the 3000 series can indeed capture the 8 minutes, just not at the same sample rate.

The 3000 scope would capture 500 seconds with a sample every 239 microseconds.

The 4000 can do it with a sample every 30 microseconds.  That's about 8x faster.

The compression waveforms are lower frequency so you would have captured the compression peaks and seen the issue with a 3000 scope, just not quite as detailed.   ;)

Tom Roberts wrote on Sep 6^th, 2009 at 3:41pm:

Quote: but can you explain how you done the running compression test with a transuducer? First, the spark plug is removed and an open compression hose is put in its place.  Then the pressure transducer is attached.  This device converts the pressures into voltages that can be displayed on the scope.  PicoScope also allows you to configure a custom probe so that these voltages are displayed in a pressure scale of your cho :) :question [smiley=happy.gif]ice.

Hello Tom great movie clip I enjoyed it very much-getting back to the compression wave form I did noticed when exhaust valve started to open the wave form was higher when the compression was low and when compression return to normal the wave form was lower

Great movie... thanks...  :)


Question:  would the exhaust valve show evidence of not seating...?

Joe,

I don't think there was any damage or evidence of poor seating on the exhaust valve but we never took it apart to see.  That was done back at the dealership.

I don't think that new head had been on there all that long though and the leakage only occurred for a short time during warm up.  Not likely enough to develop visible evidence.


Jray,

We noticed only minor differences in the shape of the compression wave when compression dropped.   The change in peak pressures was the key to the puzzle.   ;)


All Picogroup members:

There is an extensive discussion thread on this in the Picogroup area too:

http://www.autonerdz.com/cgi/yabb2/YaBB.pl?num=1242149670/0