Autonerdz forums

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

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.

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

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


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).

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.

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

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The dealer owned this one.     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.   

Rafael,

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Thanks,

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

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.

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.

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.