How does MS interpet LC-1 signal?

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tonkatoy
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Posts: 11
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How does MS interpet LC-1 signal?

Post by tonkatoy »

I'm not sure if this should be a post in tuning fuel and air or in the MegaTune sub-fourm, so apologies in advance if I've got it in the wrong spot. The third question is the main reason for the post, but the first two help provide background.

I am trying to tune my freshly built and configured project: a GM 4.3 V-6 with an Eaton M90 supercharger from a Ford SuperCoupe. It's port-injected with 37.5 lb/hr injectors running on E85. I am using a LC-1 wideband O2 sensor with with my MSII running code 2.8xx. I've got the engine to start and idle reasonable (there's still room for improvement) and my spark table is conservative and fairly rough. I am trying to use the autotune function from MegaTune to help me shape the VE table, but when I turn it on, it appears to be trying to lean out (reduce VE) to the point where the engine runs erratically and stalls out.

Question 1: :?: Should I be configured to run "seperate AFR and VE tables" or "combined AFR and VE"? From reading the manual, it would seem that it's better to use seperate tables, but how do I determine a "stoich" VE table? Since this is my first tuning project, I think it best to use the simplest method, and it seems seperate tables is only an advantage if you want to switch between fuel types, say between E85 and straight gasoline. I don't think I can do that with such big injectors and have any hope of the slow, stable idle I need for rockcrawling. :?: So would it be functionally the same to just use a combined table? If I do use seperate tables, am I correct in thinking that the autotune function will adjust the VE table to achieve the AFR target in the corosponding cell of the AFR table?

Question 2: :?: Given that I am using E85 as a fuel, should I set my AFR table to use Lambda or AFR? Most people seem to use AFR, and I conceptualize AFR numbers (for gasoline) better when doing a table. It seems that MegaTune was written with the assumption that 14.7:1 was going to be stoich. I am willing to set my tuning up either way because I really haven't gotten to far into it yet, but I don't want to be the only one on the site with an oddball configuration that makes it difficult to ask for help. Right now I am set up for Lambda because it seemed that it would be more useful down the road if I ever decided to switch fuels.

Question 3: I have not changed the configuration of my LC-1 from stock, I only performed a free-air calibration. Therefore it is set for gasoline. :?: If I am using Lambda values in the AFR table, do I need to reconfigure the output of the LC-1? I thought Lambda was Lambda, regardless of the fuel type and that the LC-1 outputs a 0-5v signal based on 1 Lambda (stoich) = 2.5v? Isn't that how MSII interpets the signal; i.e. if autotune is enabled and I am running in a cell that I have programmed to run at 1.000 lambda autotune will increase VE% if the voltage is >2.5v and reduce VE% if voltage is < 2.5v?
:?: If my understanding of how this functions is correct, why does autotune seem to drive the table so lean (almost like it is trying to reach a gasoline AFR)?

I really apologize for such a long post but until I can get unconfused about these issues, it is near useless for me to attempt to tune, and my Memorial weekend deadline for a reasonably running engine is fast approaching. Any help will be appreciated more than you can imagine.
Dean Jahnz
4.3 Chev V-6, Eaton M90 supercharger, MS-II ver. 2.89, EDIS-6
Custom multiport intake manifold 37.5 lb/hr injectors squirting E85
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Matt Cramer
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Posts: 2951
Joined: Sat Jul 03, 2004 11:35 am

Re: How does MS interpet LC-1 signal?

Post by Matt Cramer »

tonkatoy wrote:Question 1: :?: Should I be configured to run "seperate AFR and VE tables" or "combined AFR and VE"? From reading the manual, it would seem that it's better to use seperate tables, but how do I determine a "stoich" VE table? Since this is my first tuning project, I think it best to use the simplest method, and it seems seperate tables is only an advantage if you want to switch between fuel types, say between E85 and straight gasoline. I don't think I can do that with such big injectors and have any hope of the slow, stable idle I need for rockcrawling. :?: So would it be functionally the same to just use a combined table? If I do use seperate tables, am I correct in thinking that the autotune function will adjust the VE table to achieve the AFR target in the corosponding cell of the AFR table?
This is a matter of preference - if you set it to combined tables, changing the AFR table automatically change the pulse width. The autotune function (or better yet, VE Analyzer or VE Analyzer Live - MegaTune's Autotune isn't nearly as good) will work either way. MegaTune's autotune function always goes after the AFR Target table; you can set MegaLogViewer or TunerStudio to use its own table.
Question 2: :?: Given that I am using E85 as a fuel, should I set my AFR table to use Lambda or AFR? Most people seem to use AFR, and I conceptualize AFR numbers (for gasoline) better when doing a table. It seems that MegaTune was written with the assumption that 14.7:1 was going to be stoich. I am willing to set my tuning up either way because I really haven't gotten to far into it yet, but I don't want to be the only one on the site with an oddball configuration that makes it difficult to ask for help. Right now I am set up for Lambda because it seemed that it would be more useful down the road if I ever decided to switch fuels.
Either way can make sense, but you're right, MegaTune always treats 14.7:1 as stoich.
Question 3: I have not changed the configuration of my LC-1 from stock, I only performed a free-air calibration. Therefore it is set for gasoline. :?: If I am using Lambda values in the AFR table, do I need to reconfigure the output of the LC-1? I thought Lambda was Lambda, regardless of the fuel type and that the LC-1 outputs a 0-5v signal based on 1 Lambda (stoich) = 2.5v? Isn't that how MSII interpets the signal; i.e. if autotune is enabled and I am running in a cell that I have programmed to run at 1.000 lambda autotune will increase VE% if the voltage is >2.5v and reduce VE% if voltage is < 2.5v?
:?: If my understanding of how this functions is correct, why does autotune seem to drive the table so lean (almost like it is trying to reach a gasoline AFR)?

I really apologize for such a long post but until I can get unconfused about these issues, it is near useless for me to attempt to tune, and my Memorial weekend deadline for a reasonably running engine is fast approaching. Any help will be appreciated more than you can imagine.
The LC-1 measures lambda. The AFR is a calculated function. The way you have it set up will go after what will show up as a gasoline AFR - but the reading you see will be a "gasoline equivalent" AFR, not the real AFR.
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