From owner-diy_efi Tue Nov 8 20:11:31 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA15307; Tue, 8 Nov 94 20:11:31 GMT Received: from aurora.intel.com by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA15302; Tue, 8 Nov 94 15:11:27 -0500 Received: from PTD.intel.com by aurora.intel.com (5.65/10.0i); Tue, 8 Nov 94 12:09:39 -0800 Date: Tue, 8 Nov 94 12:11:13 PST From: YOU LOOK LIKE A MILLION BUCKS - ALL GREEN & WRINKLY. Message-Id: <9411082011.utk13068@PTD.intel.com> X-To: AURORA::"DIY_EFI@coulomb.eng.ohio-state.edu" Subject: RE: Dale's 68332 To: DIY_EFI Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI Speaking of 6833X systems, what is available in the area of evaluation boards for this microcontroller? Are they reasonably priced for the basement EFI'er? From owner-diy_efi Tue Nov 8 20:13:44 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA15341; Tue, 8 Nov 94 20:13:44 GMT Received: from eigen.ee.ualberta.ca by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA15336; Tue, 8 Nov 94 15:13:42 -0500 Message-Id: <9411082013.AA15336@coulomb.eng.ohio-state.edu> Received: by eigen.ee.ualberta.ca (1.37.109.4/15.6) id AA07462; Tue, 8 Nov 94 13:13:20 -0700 From: Dale Ulan Subject: Re: Dale's 68332 To: DIY_EFI Date: Tue, 8 Nov 94 13:13:20 MST In-Reply-To: <9411081529.AA13336@coulomb.eng.ohio-state.edu>; from "John S Gwynne" at Nov 08, 94 10:29 am Mailer: Elm [revision: 70.85] Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI > In message <9411080221.AA10587@coulomb.eng.ohio-state.edu> , you write: > > Sounds good... I look forward to see what you come-up with. > Is this an "open" design where you will share both the > board schematics and software source code? > Yes. I imagine I won't have source 'publishable' for a couple months as I write it... I was writing it in assembler (68000 assembler is nice to work with), and my 'real time' kernel is basically the main program loop... although the 68k does multitasking nicely, I don't find it necessary for this application. My communication with a host PC will be at 38400 (or somewhere around there), with a host program on the PC, so the 68k doesn't have to deal with a terminal-based UI. All of my development is taking place on IBM-PC based development tools. -Dale From owner-diy_efi Tue Nov 8 23:06:48 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA18614; Tue, 8 Nov 94 23:06:48 GMT Received: from shiva.trl.OZ.AU by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA18609; Tue, 8 Nov 94 18:06:34 -0500 Received: by shiva.trl.OZ.AU id AA17713 (5.65c/IDA-1.4.4 for DIY_EFI@coulomb.eng.ohio-state.edu); Wed, 9 Nov 1994 10:06:17 +1100 From: Craig Pugsley Message-Id: <199411082306.AA17713@shiva.trl.OZ.AU> Subject: Re: Found.. 8051 FAQ. To: DIY_EFI Date: Wed, 9 Nov 1994 10:06:16 +1100 (EST) Cc: ciciora@spot.Colorado.EDU In-Reply-To: <199411082019.AA14690@tomcat.al.noaa.gov> from "Ciciora Steve" at Nov 8, 94 01:10:39 pm X-Mailer: ELM [version 2.4 PL20] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 1976 Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI > >This is what I plan to do to get it running: > > > >I'm going to just use a "3-D" look-up table, with RPM on one axis and > >load on the other (load being just engine vacuum level for starters). > >The location pointed to by RPM and load will be a number that is used > >for a counter that turns on the injectors: > > > >I plan to use 4 bits (=16 points) for the RPM axis and 5 bits (=32 > >points) for the load axis, giving a total of 512 settings - (Co > >incidentally the same way that other well known controllers are laid > >out). > > > >Craig. > > > > It sounds like your line of reasoning is very similar to mine! I'm > working on some code to do 4 point linear interpolation for the fuel map. > My fuel map will take an 8 bit number (0->255) for the engine RPM and an > 8 bit number for the engine load. One problem with using a 255 RPM x 255 LOAD = 64K settings - impractical (impossible) to calibrate each and every one of those points. I guess you could do your on dyno/road calibration with something like what I suggested above (32 load settings x 16 rpm settngs) and then linearly interpolate the intermediate settings (Either in real time in the processor or via a PC and program the memory with the full 255x255 map) > My map will be 17 x 17 x 8 bit numbers. IE (17 load x 17 rpm settings?) I'm un-decided if an 8 bit injection time will have enough 'dynamic range' from idle to full throttle, though it's probably easier to deal with an 8 bit number. > Even though i will use the upper 4 bits (0->15) > for the lookup of the map, to get a point on either side of the 0->15 > number you need 17 points, hence the 17 x 17 map instead of 16 x 16. > >From then I will use the lower 4 bits to do a 4 point linear interpolation. Sorry, I don't understand. Can you explain it in a bit more detail? (Maybe an ASCII diagram) Thanks for re-posting the fuel amount theory article. (I have it somewhere but finding it is another story) Craig. From owner-diy_efi Tue Nov 8 23:29:14 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA18806; Tue, 8 Nov 94 23:29:14 GMT Received: from pine.cse.nau.edu by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA18801; Tue, 8 Nov 94 18:29:11 -0500 Received: (from met@localhost) by pine.cse.nau.edu (8.6.9/2.2-nau) id QAA10182 for diy_efi@coulomb.eng.ohio-state.edu; Tue, 8 Nov 1994 16:29:08 -0700 Message-Id: <199411082329.QAA10182@pine.cse.nau.edu> From: met@pine.cse.nau.edu (MTN-KAT) Date: Tue, 8 Nov 1994 16:29:08 -0700 X-Mailer: Mail User's Shell (7.2.5 10/14/92) To: diy_efi Subject: Electronics suppliers? Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI I have a Digikey catalog, they don't seem to cover the components that I need. Could some of y'all give me some names and numbers? I was using my 800 directory, after several wrong numbers I checked the issue date, 1987! Just a bit out of date, eh? Thanks! Millam From owner-diy_efi Tue Nov 8 23:41:22 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA18883; Tue, 8 Nov 94 23:41:22 GMT Received: from hp-cv.cv.hp.com by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA18878; Tue, 8 Nov 94 18:41:15 -0500 Received: from hp-pcd.cv.hp.com by hp-cv.cv.hp.com with SMTP (1.36.108.7/15.5+IOS 3.22+CV 1.0ext) id AA12131; Tue, 8 Nov 1994 15:41:00 -0800 Received: from hpcvts.cv.hp.com by hp-pcd.cv.hp.com with SMTP (1.37.109.8/15.5+IOS 3.22+OM+CV 1.0) id AA04607; Tue, 8 Nov 1994 15:40:59 -0800 Received: by hpcvts.cv.hp.com (15.11/15.5+IOS 3.22[SMTP-rly]+CV 1.0leaf) id AA23010; Tue, 8 Nov 94 15:43:12 pst From: Cary McCallister Message-Id: <9411082343.AA23010@hpcvts.cv.hp.com> Subject: 800 numbers To: DIY_EFI Date: Tue, 8 Nov 94 15:43:11 PST In-Reply-To: <199411082329.QAA10182@pine.cse.nau.edu>; from "MTN-KAT" at Nov 8, 94 4:29 pm Mailer: Elm [revision: 64.9] Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI > >I was using my 800 directory, after several wrong numbers I checked the issue >date, 1987! Just a bit out of date, eh? You might try using the online version. URL http://att.net/dir800 Cary From owner-diy_efi Wed Nov 9 03:49:31 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA20169; Wed, 9 Nov 94 03:49:31 GMT Received: from shiva.trl.OZ.AU by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA20164; Tue, 8 Nov 94 22:49:18 -0500 Received: by shiva.trl.OZ.AU id AA28733 (5.65c/IDA-1.4.4 for DIY_EFI@coulomb.eng.ohio-state.edu); Wed, 9 Nov 1994 14:49:00 +1100 From: Craig Pugsley Message-Id: <199411090349.AA28733@shiva.trl.OZ.AU> Subject: Re: FW: 67F687 To: DIY_EFI Date: Wed, 9 Nov 1994 14:48:51 +1100 (EST) In-Reply-To: <199411081750.AA14247@tomcat.al.noaa.gov> from "Ciciora Steve" at Nov 8, 94 10:41:48 am X-Mailer: ELM [version 2.4 PL20] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 437 Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI Hi there, I just looked up the 67F687 data sheet - wow! This baby's got it all. 55 pages, looks like it will work w/8 bit micros. I rang up for pricing, and was told in 1 off qtys it's $AUS 48.10 each (Which is $US 36 approx) - I think the hardware contained in the chip would reduce your programming load by half. (& in a commercial design with the numbers ground off anyone copying your design wouldn't know WHAT it was ;-) Craig. From owner-diy_efi Wed Nov 9 04:06:12 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA20207; Wed, 9 Nov 94 04:06:12 GMT Received: from [199.98.14.33] by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA20202; Tue, 8 Nov 94 23:06:02 -0500 Received: (from jeff@localhost) by prufrock.bga.com (8.6.8/8.6.6) id WAA03745 for DIY_EFI@coulomb.eng.ohio-state.edu; Tue, 8 Nov 1994 22:05:55 -0600 From: Jeff Francis Message-Id: <199411090405.WAA03745@prufrock.bga.com> Subject: Re: Electronics suppliers? To: DIY_EFI Date: Tue, 8 Nov 1994 22:05:55 -0600 (CST) In-Reply-To: <199411082329.QAA10182@pine.cse.nau.edu> from "MTN-KAT" at Nov 8, 94 04:29:08 pm X-Mailer: ELM [version 2.4 PL23beta2] Content-Type: text Content-Length: 1261 Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI According to MTN-KAT: > I have a Digikey catalog, they don't seem to cover the components that I need. > Could some of y'all give me some names and numbers? > I was using my 800 directory, after several wrong numbers I checked the issue > date, 1987! Just a bit out of date, eh? I'm not sure exactly what you need for components, but I've ordered from Jameco in the past. 1-800-831-4242. They have no minimum order (!!!), though there is a $5 "processing fee" for orders under $25. I've also purchased through JDR MicroDevices. I was *very* pleased with them. They have friendly, helpful order-takers and very speedy delivery. Note that this was about a year ago. Haven't ordered many goodies lately. Don't have a catalog handy for a phone number, but it should be available from 800 Directory Assistance. -- Jeff Francis ------------------------------------- 1 512 444 4003 (home) Ligneous and petrous projectiles can 1 512 795 3010 (work) potentially fracture my osseous Austin, TX USA structure, but pejorative appelations jeff@prufrock.bga.com (home) will forever remain innocuous. Jeff_Francis@sns.net (work) ------------------------------------- From owner-diy_efi Wed Nov 9 22:30:45 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA23176; Wed, 9 Nov 94 22:30:45 GMT Received: from tomcat.al.noaa.gov by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA23168; Wed, 9 Nov 94 17:30:41 -0500 Received: from aztec.al.noaa.gov by tomcat.al.noaa.gov with SMTP id AA00507 (5.65c/IDA-1.4.4 for ); Wed, 9 Nov 1994 15:37:29 -0700 Message-Id: <199411092237.AA00507@tomcat.al.noaa.gov> Date: 9 Nov 1994 15:29:10 -0700 From: "Ciciora Steve" Subject: FW: Re: Found.. 8051 FAQ. To: DIY_EFI Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI (stuff deleted) >> It sounds like your line of reasoning is very similar to mine! I'm >> working on some code to do 4 point linear interpolation for the fuel map. >> My fuel map will take an 8 bit number (0->255) for the engine RPM and an >> 8 bit number for the engine load. >One problem with using a 255 RPM x 255 LOAD = 64K settings - >impractical >(impossible) to calibrate each and every one of those points. No, you misunderstood. The map in the EFI box has 17 x 17 x 8 bits = 289 bytes stored. These are the values the user can modify. What I do is 4 point linear interpolation between the 4 points nearest to the desired value. Impractical/impossible? Remember Y=mX + B? Just do it 3 times using integer math. The results (the way I do it) is a 16 bit number. Just use the number of Most Significant Bits you need. At this point I'm not willing to guess how many bits I will need. I only use the 4 most significant bits of the 8 bit load and the 8 bit RPM numbers to get my 4 points from my table to interpolate between. 16 RPM x 16 Load = 256 values. If you want a data point on each side of these 256 values, you can use a 17 x 17 point table. I use the 4 least significant bits to scale between the 17 x 17 data points. >I guess you could do your on dyno/road calibration with something >like >what I suggested above (32 load settings x 16 rpm settngs) and then >linearly interpolate the intermediate settings (Either in real time >in >the processor or via a PC and program the memory with the full >255x255 map) Yup. I'm only guessing that a 17 x 17 map will be enough. What did you base your decision on using 32 load numbers on? Do you know something I don't? >> My map will be 17 x 17 x 8 bit numbers. >IE (17 load x 17 rpm settings?) Yup. >I'm un-decided if an 8 bit injection time will have enough 'dynamic >range' from idle to full throttle, though it's probably easier to >deal with an 8 bit number. My 4 bit linear interpolation code returns a 16 bit result. I'm sure that 16 bits is more than needed, and would not be suprised if 8 bits is enough. I'm not that far along to decide (yet...). - Steven Ciciora From owner-diy_efi Thu Nov 10 01:14:44 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA23782; Thu, 10 Nov 94 01:14:44 GMT Received: from uclink3.Berkeley.EDU by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA23777; Wed, 9 Nov 94 20:14:40 -0500 Received: from uclink.berkeley.edu by uclink3.berkeley.edu (8.6.8/1.33(web)-OV2) id RAA20528; Wed, 9 Nov 1994 17:14:38 -0800 Received: by uclink.berkeley.edu (8.6.9/1.33(web)-OV4) id RAA09960; Wed, 9 Nov 1994 17:14:30 -0800 Date: Wed, 9 Nov 1994 17:14:29 -0800 (PST) From: James C Patterson Subject: Carb adjustment using exhaust temp... To: Electronic Fuel Injection In-Reply-To: <199411092340.PAA05490@uclink3.berkeley.edu> Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI This is somewhat off the aim of this group but until I do an EFI I might as well use what I've got. Someone at one point (I think it was this list) mentioned using thermocouples in the exhaust (one per cylinder) to measure for mixture and balance. What type of readings would you be looking for? Higher temperatures on lean burning or just the opposite? And are there actual values to look for other then the realitive Delta-T? The engine is a Nissan staight 6 with dual carbs, therefore the mixture balance issue. If I can work this out it will very simple to install sheathed thermocouples in the air injection ports of the header and run a data-logger to pull up some real-time info of actual use. James james@uclink.berkeley.edu From owner-diy_efi Thu Nov 10 01:14:46 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA23787; Thu, 10 Nov 94 01:14:46 GMT Received: from shiva.trl.OZ.AU by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA23775; Wed, 9 Nov 94 20:14:35 -0500 Received: by shiva.trl.OZ.AU id AA16364 (5.65c/IDA-1.4.4 for DIY_EFI@coulomb.eng.ohio-state.edu); Thu, 10 Nov 1994 12:14:11 +1100 From: Craig Pugsley Message-Id: <199411100114.AA16364@shiva.trl.OZ.AU> Subject: EFI mapping ideas. To: DIY_EFI Date: Thu, 10 Nov 1994 12:14:08 +1100 (EST) In-Reply-To: <199411092237.AA00507@tomcat.al.noaa.gov> from "Ciciora Steve" at Nov 9, 94 03:29:10 pm X-Mailer: ELM [version 2.4 PL20] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 2519 Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI > >One problem with using a 255 RPM x 255 LOAD = 64K settings - >impractical > >(impossible) to calibrate each and every one of those points. > > No, you misunderstood. The map in the EFI box has 17 x 17 x 8 bits = 289 bytes > stored. These are the values the user can modify. What I do is 4 point linear > interpolation between the 4 points nearest to the desired value. OK, so the user has to calibrate 289 points, right? -A lot less than 64K :-) Then you interpolate between the settings if the value. EG: Injector on-time | | **# | #* ** | * *# (#= user calibrated) | * (*= computer interpolated) | * | # |_______________________ LOAD (= vacuum) ^ ^ ^ ^ (^=points where the user calibrates) (At a fixed engine RPM) So, you are interpolating between 2 points on the RPM axis and 2 points on the Load axis, making an overall interpolation between 4 points? If it works properly it should be quite nice. > Yup. I'm only guessing that a 17 x 17 map will be enough. What did you base > your decision on using 32 load numbers on? Do you know something I don't? From what I can determine, the load is much more important than the RPM. (I did some measurements of an aftermarket computer, and the pulse time the injector was on for did not vary with RPM (Well, when under engine vacuum. When under boost it did) The 32 load points is what several well known computers use (EG Haltech). If you're using interpolation 32 wouldn't matter, you might even get away with something as low as 4 or 8. I'd say 17x17 w/interpolation should be more than adaquate. In the initial stages I won't be using interpolation, hence using 32 bits. > >I'm un-decided if an 8 bit injection time will have enough 'dynamic > >range' from idle to full throttle, though it's probably easier to >deal with > an 8 bit number. > > My 4 bit linear interpolation code returns a 16 bit result. I'm sure that 16 > bits is more than needed, and would not be suprised if 8 bits is enough. I'm > not that far along to decide (yet...). I think that the 16bits you get out of interpolation from 8 bit numbers can still only really be considered to be 8 bit accurate. HOWEVER, I might well be missing something here (Take the above comment as being possible/probably incorrect). If 8 bits is accurate enough for fuel metering there won't be a problem anyway. Anyone else on the list like to comment about their fuel mapping ideas? Craig. pugsley@trl.oz.au From owner-diy_efi Thu Nov 10 03:14:15 1994 Received: by coulomb.eng.ohio-state.edu (920330.SGI/920502.SGI) id AA24629; Thu, 10 Nov 94 03:14:15 GMT Received: from relay4.UU.NET by coulomb.eng.ohio-state.edu via SMTP (920330.SGI/920502.SGI) for /usr/local/mail/majordomo-1.92/wrapper resend -p bulk -M 10000 -l Diy_Efi -f Diy_Efi-Owner -h coulomb.eng.ohio-state.edu -s -r DIY_EFI diy_efi-outgoing id AA24624; Wed, 9 Nov 94 22:13:57 -0500 Received: from offramp.dsccc.com by relay4.UU.NET with SMTP id QQxpiy00910; Wed, 9 Nov 1994 22:13:53 -0500 Received: by offramp.dsccc.com (5.67b/SMI-V1.8) id AA26243; Wed, 9 Nov 1994 21:14:33 -0600 Received: from onramp(192.245.102.129) by offramp via smap (V1.3mjr) id sma026238; Wed Nov 9 21:14:15 1994 Received: from optilink.dsccc.com by camelot.dsccc.com (5.65c/SMI-V1.8) id AA20901; Wed, 9 Nov 1994 21:14:39 -0600 Received: from hayesss2 by optilink.dsccc.com (4.1/SMI-4.0) id AA19425; Wed, 9 Nov 94 19:13:17 PST From: klemm@optilink.dsccc.com (Joe Klemm) Received: by hayesss2 (4.1) id AA10431; Wed, 9 Nov 94 19:13:14 PST Date: Wed, 9 Nov 94 19:13:14 PST Message-Id: <9411100313.AA10431@hayesss2> To: DIY_EFI Subject: Re: EFI mapping ideas. Sender: owner-diy_efi Precedence: bulk Reply-To: DIY_EFI I'm not sure if I understand the fuel mapping 4 point linear interpolation correctly. But it seems to me if you interpolate 4 points between two 8 bit numbers what you get is almost a 10 bit value (1020 values compared to 1024) not 16. I did this a few years ago while temperture characterizing a VCO and it worked fine. But each time you add an interpolated point you only increase the resolution by one bit.