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Okay....here's a quick rundown of what I did for better gas mileage via EGR in the chip. I hope to write a more detailed "how-to" in the near future.
I had spoken with BG sometime ago on this subject, and we spoke about how almost anyone who tried to get better gas mileage via F29 or F30 would run into problems with fueling transition from this lean cruise spot to other places (accel, decel, stabbing it, etc...). My truck (back when I used to lean out F29) would have a bad stumble on the freeway when you'd accelerate out of this cruise condition.
The cure? Use the EGR tables to pinpoint the area you want to address fueling at and keep the VE tables the same (for the most part). Obviously, this requires a truck to have the EGR blocked off, but from there, just enable EGR at whatever temp you'd like via 0x06CD (KEGRTEM1). I set mine to enable only in fully warmed up conditions since all other extraneous fueling factors (coolant temp dependent tables, etc....) would be out of the equation.
Once enabled, there are 3 main tables to concentrate on......the first:
F4 - 0x02FF - EGR Spark Advance vs %EGR..........this table adds in timing to the total timing advance during whatever condition (in this case %EGR). For the most part, my truck responded best to a max of 2-3 degrees advance with timing tapering off as the % decreased (affected by F72....just a minute ;-)). Remember this table only adds advance when the EGR is enabled, so it's a non factor as soon as you exceed the EGR enable criteria.
next........
F72 - 0x06E5 - Desired EGR % vs Vac & RPM.........this table controls the amount of EGR "emphasis". Basically, it has control over F4 and F28 and when and how much desired EGR is allowed dependent on Vac & RPM. Obviously, cruise conditions are between 1600 and 2400 and 10-20" vac for most trucks, so that's where I put emphasis. I found that if you have too much desired EGR at too low a vac reading (10" to 0), that you could still run into some stumbling issues. For my truck, this range (10" to 0) was a point of accel and a lot of EGR was not needed (none in my case), so I had the desired EGR taper off towards this range (as well as my timing in F4 and my "lean-ness" in F28). Another thing I noticed is that this table doesn't quite match actual real world vac readings. Might just be my truck/gauge, but you may run into this also.......15 in the table was actually closer to 10 real world for me IIRC. I didn't really go too high (1-12%) on the desired EGR in this table either, since the range I was tuning for is so small (1600-2400 and 10-20" vac). It also has a huge effect on F28, which I'll get to in just a second. I can go into further detail about this table, but that's it's immediate and most noticeable affect.
lastly........
F28 - 0x040E - Base Pulse Constant vs Desired EGR..............this table is a direct fueling multiplier based on desired EGR %. This value needs to be numerically lower when EGR is commanded. I tested the limits of this and lets just say that you can render the truck useless if not careful (you can go WAY lean).....so use baby steps here. I started off by dropping each value from 1-12.8 (see desired EGR % in F72 - above) about .002 points (from 89 to 87) and testing. Basically, I'd get to freeway speeds and with wideband and Datamaster handy, I'd see which desired EGR % (vac dependent via F72) was where I wanted the fueling to be, then go back and adjust from there. Where did I wind up? Well my truck would have a bit of a stumble coming out of EGR command (accel), so I added some fuel to the 1.6 value of F28 to help the transition. Didn't take much to make all the difference. As far as how lean to go.....that will ultimately lie with your build and comfort level. I went from .091 to .077 from 1.6 to 12.8 (.002 increments stepped accordingly) on my chip. This table can be gone into with further detail later as well, but that's it's main function. Remember, this table DIRECTLY affects your fueling, so watch your O2 and check your plugs!
My truck really likes it this way. With the timing tapering off towards lower desired EGR %, I have no stumble during transition and regularly see around 20-22 mpg (up from 17-19) at freeway speeds when driven "sensibly". Obviously YMMV, and your tune may not take to this mod as well as mine did, but it's a worthwhile test anyways.
Oh yeah.........don't forget to disable Code 32. :-)
I had spoken with BG sometime ago on this subject, and we spoke about how almost anyone who tried to get better gas mileage via F29 or F30 would run into problems with fueling transition from this lean cruise spot to other places (accel, decel, stabbing it, etc...). My truck (back when I used to lean out F29) would have a bad stumble on the freeway when you'd accelerate out of this cruise condition.
The cure? Use the EGR tables to pinpoint the area you want to address fueling at and keep the VE tables the same (for the most part). Obviously, this requires a truck to have the EGR blocked off, but from there, just enable EGR at whatever temp you'd like via 0x06CD (KEGRTEM1). I set mine to enable only in fully warmed up conditions since all other extraneous fueling factors (coolant temp dependent tables, etc....) would be out of the equation.
Once enabled, there are 3 main tables to concentrate on......the first:
F4 - 0x02FF - EGR Spark Advance vs %EGR..........this table adds in timing to the total timing advance during whatever condition (in this case %EGR). For the most part, my truck responded best to a max of 2-3 degrees advance with timing tapering off as the % decreased (affected by F72....just a minute ;-)). Remember this table only adds advance when the EGR is enabled, so it's a non factor as soon as you exceed the EGR enable criteria.
next........
F72 - 0x06E5 - Desired EGR % vs Vac & RPM.........this table controls the amount of EGR "emphasis". Basically, it has control over F4 and F28 and when and how much desired EGR is allowed dependent on Vac & RPM. Obviously, cruise conditions are between 1600 and 2400 and 10-20" vac for most trucks, so that's where I put emphasis. I found that if you have too much desired EGR at too low a vac reading (10" to 0), that you could still run into some stumbling issues. For my truck, this range (10" to 0) was a point of accel and a lot of EGR was not needed (none in my case), so I had the desired EGR taper off towards this range (as well as my timing in F4 and my "lean-ness" in F28). Another thing I noticed is that this table doesn't quite match actual real world vac readings. Might just be my truck/gauge, but you may run into this also.......15 in the table was actually closer to 10 real world for me IIRC. I didn't really go too high (1-12%) on the desired EGR in this table either, since the range I was tuning for is so small (1600-2400 and 10-20" vac). It also has a huge effect on F28, which I'll get to in just a second. I can go into further detail about this table, but that's it's immediate and most noticeable affect.
lastly........
F28 - 0x040E - Base Pulse Constant vs Desired EGR..............this table is a direct fueling multiplier based on desired EGR %. This value needs to be numerically lower when EGR is commanded. I tested the limits of this and lets just say that you can render the truck useless if not careful (you can go WAY lean).....so use baby steps here. I started off by dropping each value from 1-12.8 (see desired EGR % in F72 - above) about .002 points (from 89 to 87) and testing. Basically, I'd get to freeway speeds and with wideband and Datamaster handy, I'd see which desired EGR % (vac dependent via F72) was where I wanted the fueling to be, then go back and adjust from there. Where did I wind up? Well my truck would have a bit of a stumble coming out of EGR command (accel), so I added some fuel to the 1.6 value of F28 to help the transition. Didn't take much to make all the difference. As far as how lean to go.....that will ultimately lie with your build and comfort level. I went from .091 to .077 from 1.6 to 12.8 (.002 increments stepped accordingly) on my chip. This table can be gone into with further detail later as well, but that's it's main function. Remember, this table DIRECTLY affects your fueling, so watch your O2 and check your plugs!
My truck really likes it this way. With the timing tapering off towards lower desired EGR %, I have no stumble during transition and regularly see around 20-22 mpg (up from 17-19) at freeway speeds when driven "sensibly". Obviously YMMV, and your tune may not take to this mod as well as mine did, but it's a worthwhile test anyways.
Oh yeah.........don't forget to disable Code 32. :-)