They don't call it FUEL CUT for nothing! (Vid and pic)

MK3Brent

Very expensive....
Aug 1, 2005
2,878
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Greensboro and Greenville NC
I was looking though my old dyno files, and found this gem.

p578935_1.jpg


I had accidentally over boosted, and hit FCO.
That AFR line is really scary, LOL!

Here is the video when it happened.
http://youtube.com/watch?v=bDT7wNY_TsY
 

tissimo

Stock is boring :(
Apr 5, 2005
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Melbourne, FL
the a/f at that point doesn't mean anything, as long s the engine was tuned before and ran ok a/fs you'd be fine.. at the point of fuel cut it dumps pure o2 into your tail pipe so ofcourse it will read lean
 

MK3Brent

Very expensive....
Aug 1, 2005
2,878
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Greensboro and Greenville NC
Basically injectors off. :rofl:

tissimo said:
the a/f at that point doesn't mean anything, as long s the engine was tuned before and ran ok a/fs you'd be fine.. at the point of fuel cut it dumps pure o2 into your tail pipe so ofcourse it will read lean


Oh I know, I'm not worried or anything... I just thought it was neat on the chart.
 

MassSupra89

Almost done.
Nov 3, 2005
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MA
Yea it makes sense now, So would the dips in the top graph be when it's just passing air through the cylinder with no combustion(obviously making no power)?
 

Figit090

Fastest mk3 GT4 1/4 mile!
Jan 7, 2006
1,835
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Humboldt County
can someone tell me why a faulty injector can burn up a cylinder?

and how can running lean on a 4 stroke (as opposed to a fuel-lubricated 2 stroke) cause problems? is it the time of the explosion?

kinda random, but it seemed like it would fit nicely here.
 

tissimo

Stock is boring :(
Apr 5, 2005
4,238
0
0
40
Melbourne, FL
Figit090 said:
can someone tell me why a faulty injector can burn up a cylinder?

and how can running lean on a 4 stroke (as opposed to a fuel-lubricated 2 stroke) cause problems? is it the time of the explosion?

kinda random, but it seemed like it would fit nicely here.
Theres several kinds of faulty injectors.. if one is spraying less fuel it could run lean, cause detonation in that one cyl where as the rest have perfectly fine a/fs and your overall a/f is fine.. an Injector just not working wouldn't burn anything up..
 

TurboStreetCar

Formerly Nosechunks
Feb 25, 2006
2,778
13
38
Long Island, Ny
Although we kno its Fuel thats cut, A lean spike in the a/f doesnt nessesaraly mean that fuel was cut. it means there was a misfire but the A/F controller couldnt tell you if it was fuel related or spark related.

"can someone tell me why a faulty injector can burn up a cylinder?

and how can running lean on a 4 stroke (as opposed to a fuel-lubricated 2 stroke) cause problems? is it the time of the explosion?"

Its Not only a concern of detonation but also a Lean mixture burns very hot, hot enough to melt pistons. If ONE injector was somewhat clogged and causing AF's about 12.5 or higher at full throttle high boost, there could be enough heat generated to melt pistons and or detonate and Blow holes in the piston. 12.5 is about the safe limit, 12.5 is fast but dangerous, i prefer <12 AF's more like 11.7-11.5

a 2 stroke engine can be damaged from lean mixtures as well but the oxygen content isnt as high in the cylinder due to the design on the engine, they dont breathe as efficient as a 4 stroke. This lowers combustion temps so they have more leeway to lean mixtures because it doesnt burn as hot. Not to mention the oil in the CC as well. well at least AFAIK.