distinguishing between rich misfire and lean condition

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Yves
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distinguishing between rich misfire and lean condition

Post by Yves »

How can you distinguish between a rich misfire and a genuine lean condition ?
Matt Cramer
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Re: distinguishing between rich misfire and lean condition

Post by Matt Cramer »

Usually, a rich misfire will be reading rich before and after it happens. Lean conditions are prolonged and a fairly smooth reading.
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Rick Finsta
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Re: distinguishing between rich misfire and lean condition

Post by Rick Finsta »

Also, you can shut it down and pull a plug.
Yves
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Re: distinguishing between rich misfire and lean condition

Post by Yves »

Rick Finsta wrote:Also, you can shut it down and pull a plug.
Rather difficult proposition to do on the side of the road and I'm not sure a misfire would show up on a plug.

I would think it would show up in the logs in some way.
dontz125
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Re: distinguishing between rich misfire and lean condition

Post by dontz125 »

A misfire won't show in and of itself, but a sustained rich vs lean condition would be obvious. As to the difficulty or convenience of pulling a plug, that will vary from situation to situation, but the simple plug chop is a time tested means of determining what your engine is doing.
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whittlebeast
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Re: distinguishing between rich misfire and lean condition

Post by whittlebeast »

See www.nbs-stl.com/tuning

Do the MAPxRPM vs duty cycle plot and normally the problem will jump out at you. If there is one....
Yves
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Re: distinguishing between rich misfire and lean condition

Post by Yves »

Am I right the formula for RPMXMAP is [MAP]*[RPM]/100 ?

I'm not sure what I'm supposed to see jumping at me ? Sorry no experience with the scatter plots.
Rick Finsta
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Re: distinguishing between rich misfire and lean condition

Post by Rick Finsta »

Yes it is "[MAP]*[RPM]/100" with the parentheses removed. Plot it versus Duty Cycle and you should get a linear regression from the origin to the top right. Also if you plot VE on the Z axis you should see a nice smooth color change from blue to red.
Yves
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Re: distinguishing between rich misfire and lean condition

Post by Yves »

This is what I get. I have difficulty in seeing something in it (Maybe there is nothing). I do see the line going in a curve from the bottom left to the top right.

Image

I also plotted RPM/MAP/TP vs RPM/MAP/PW to see it was similar as explained in the link above :

Image

if the info in that link is correct these plots would indicate it could run just as easily on Alpha-N
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Re: distinguishing between rich misfire and lean condition

Post by Rick Finsta »

Out of curiosity, make another custom field for TPSxRPM and see what the TPSxRPM versus DC looks like relative to the MAP-calculated one. On my engine I get more linearity with the MAPxRPM function, and the TPSxRPM function has some odd nodes on it and looks logarithmic in nature.
Yves
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Re: distinguishing between rich misfire and lean condition

Post by Yves »

Image
Rick Finsta
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Re: distinguishing between rich misfire and lean condition

Post by Rick Finsta »

So, instead of a nice tight linear function, you've got a wide spread and a lot of waviness to the graphs. The TPS based function looks to me to be a lot tighter in your idle and cruising range, which tells me that Alpha-N would work well there (I'm open to criticism on that conjecture). Perhaps it is time to look at a Alpha-N/Speed Density hybrid setup? IIRC you said you've got ITBs fed from independant plena per bank, correct?

I'd love to hear someone's explanation as to why you get some much waviness in those plots up top.

For reference, this is what my tune looks like so far with a dual plane intake, bank to bank fueling, and single 4150 style throttle body:

Image

Notice also how instead of plotting AFR in the Z axis I'm using VE - this is a nice way to visualize how the cylinders are filling relative to what your injectors are doing.

Also, if I filter transients the plot gets tighter but I simply don't have enough data up top to draw conclusions yet, IMHO.
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Re: distinguishing between rich misfire and lean condition

Post by whittlebeast »

I have found that ITB setups want to run SD below about 15% throttle. Above that angle, the effective trumpet length of the intake tract starts winding up making the tuning best handled with Alpha-N.

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Yves
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Re: distinguishing between rich misfire and lean condition

Post by Yves »

Have to add the tune is not quite right.
Not a lot of high rpm, high load driving done in that log.

So you think that ITB load would be better.

And yes, each bank has it's own airbox feeding the stacks and each airbox has a seperate air filter (K&N cone filter)
Yves
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Re: distinguishing between rich misfire and lean condition

Post by Yves »

So, what would be the best way to go here ? Stay on SD or go to ITBload. If I base the switchpoint on 90% VE the division will be somewhere in the top right corner.
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