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Anatomy of a cracked piston Posted by SWEDECAR [Email]  (#112)  [Profile/Gallery]
(more from SWEDECAR) on Fri, 19 Oct 2007 19:11:43
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Some of you might know by now that the B205/235 engine have a bad habit of cracking pistons.
This is what it can look like.
It started with the Viggen engine in 99 being a souped up B235 and have continued since then here and there.
One of the common believes are that the air mass meter could be at fault, slowly going bad and when doing that as air mass meters do, leaning out the fuel mixture creating a much hotter burn and pinging.
One of my pet peeves is also the K&N air filter that I see more of in Saab's than in Volvo's and also that the K&N filter is factory install in the Viggen.
I don't believe in placing an "oil drench" filter right in front of the air mass meter element allowing oil particles to get sucked in and ram the air mass meter and after that it catches the small particles that inevitable will pass through the filter.
On this particular car, #1 piston was cracked and combustion gases had worked as a blow torch spraying aluminum dust on the connecting rod.
When I was done with the work and test drove the car, I took a good look at the air mass meter correction value with my Tech 2 during a steady acceleration and noticed a dropping value where after I accelerated going down to about -14.
I also noticed a very erratic turbo boost being sluggish to begin with and then when the boost built up, I could hear a fair share of engine pinging.
By the way, this car was equipped with a (shudder) a K&N air filter.
Back at the shop I removed the air mass meter and cleaned out the element and installed a paper filter.
Next test drive, I had a turbo boost that built steady and straight right up to red area of gauge and almost no pinging.
Also, the steady acceleration test revealed an air mass meter correction value of no more than -5 but with a lot more of the trace/value being on the positive side of the spectrum as well.
I have starting to use that AMM correction value more and more when tracking faults. It will react on many things like a vacuum leak for example.
Just some info for the interested.
Anders
, Fri, 19 Oct 2007 19:11:43 <-- Viewing This Message, Tue, 23 Oct 2007 09:54:04, Sun, 21 Oct 2007 21:20:20, Sat, 20 Oct 2007 10:03:07, Sun, 21 Oct 2007 21:25:09
, Fri, 19 Oct 2007 21:08:25
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