lean area around 2500ish rpms-2014 ctsv

[GHuggins]

no dice...I zero'd all those out and still is there..dammmit

It may still yet come. Just have to get Will set up and do some digging I still think there's a test or torque management going on. With the years being newer than 12' those timer tables won't work anyway. Their hook coding is apparently missing or how ever one would phrase that.

[sgod1100]

It may still yet come. Just have to get Will set up and do some digging I still think there's a test or torque management going on. With the years being newer than 12' those timer tables won't work anyway. Their hook coding is apparently missing or how ever one would phrase that.

it's got to be something little and stupid going on..lol. Who's Will?

[JayRolla]

For fun threw 20% fuel with VVE and MAF and still spiked. It's so freaking annoying. I tried zero on all the torque tables and nothing.

[sgod1100]

For fun threw 20% fuel with VVE and MAF and still spiked. It's so freaking annoying. I tried zero on all the torque tables and nothing.

Yup..I did about 20-25% addition a few years ago as well....same thing...lol.

[L1FTD]

Hi Guys,

Bit of a long post, but might be of some use to those experiencing this annoying phenomenon with their LSA.

I experience the same lean areas. Tried all the above, and many combinations of disabling/zeroing/maxing/fine tuning random parameters. Don't need to go over that, we all know.

I'm hoping the true fix is a simple disable of some unseen test we can't access yet, but starting to feel its more of a mechanical/inherent problem with the LSA in a certain power range. Stock LSA engine (stock cam), boost/bolt-ons, and oversized (room-to-grow) injectors.

The below isn't a fix of the underlying cause, but did get me to the point of a smooth AFR with no PE rape. This is also only a fix for WOT, also leading me to believe it may not be fixable under light-load until the engine is in a higher power bracket.

- The higher the Inj. PW I could get going through the 1400-2800rpm range, the less of a lean spike. ID1050X on a setup making 600rwhp = only 20-25% IDC, using stock fuel pressure, through the 1400-2800rpm. On a setup making 700+rwhp, I'm sure the IDC would be up.

- Lower the Low Flow Fuel Pressure (ECM 7031) to 310kPa / 45PSI

- Raise the Low Flow Upper Condition (ECM 17020) to a point where changeover to normal flow occurs at a minimum of 2800rpm (raise the Low Flow Lower Condition to match the factory drop for the new upper values). I.E. if your flowing 26g/s fuel at 2800, put 26 in 2800 and lower, keeping above 2800 stock. The g/s will change with fuel need variance, so something high enough to make 2800rpm the minimum in winter/summer etc. I've changed to normal flow at 3200rpm without problem, but unnecessary as the lean event is well over.

- If you're running a BAP, which most will be, I've found altering the Fuel Pump Openloop DC (FSCM 6997) to stabilize oscillating fuel pressure. Very helpful when running the low flow at 45PSI. As system voltage increases, the pump DC is multiplied down. My BAP puts out 17.5V at 3PSI, but the pump DC is being multiplied down by system volts of only 14.8V.

- For ease of testing, I made Fuel System Voltage Min. (ECM 18102) 15V across the board. This gives me 14.8-14.9V in the scanner.

- Calculate the multiplier the ECM/FSCM would apply to the openloop DC if you're BAP volts were system volts. Calculate the difference between your current multiplier (based on system volts), and your BAP multiplier. Multiply the openloop DC table by the difference.

- Example, if your BAP puts out 17.5V, referencing Openloop DC Multi. (FSCM 6998), this would be a multiplier of 0.682 (as far as I'm aware, the system can't see this). If your system volts is 14.8V, a multiplier of 0.8086 is being applied to the openloop DC table. Easiest way to bring the DC values down to where they will line up with system volts multiplier plus BAP multiplier, is multiply the table by the full amount (e.g. 0.682 for 17.5V), remember a number from the table, then restore to stock and multiply the table by the system volts multiplier (e.g. 0.8086 for 14.8V), then multiply the table down again (one try at a time, if the multiplier didn't hit the remembered number, restore back and try a new multiplier). Once you hit the remembered number, copy the multiplier used, restore table to stock, and multiply table by the copied multiplier. For myself, that was a multiplier of 0.84345.

- Now the openloop DC table values have been brought down to where, when they are multiplied by the system volts, the number will represent as if multiplied down by the BAP voltage the system can't see.

- Note: Bringing the pump DC down will cause pump trims to rise, in my case ST trim went from 0.97 to 1.12, LT trim has remained at 1.02 for now. Unsure if the LT will slowly increment, or if the ST is actually trimming DC or it's just a reference of how far it thinks DC is off.

- The DC reduction has smoothed out the fuel pressure oscillations, commanded DC oscillations, and pressure spikes transitioning from low flow > normal flow > high flow.

- I also lowered the Normal Flow pressure (ECM 7033) to 380kPa / 55PSI, just to keep the pressure rises consistent (10PSI jump at a time).

- If you wanted to keep the Fuel System Voltage Minimum stock (i.e. 12.5V > 14.5V based on fuel flow), the above could be applied based on when your BAP kicks-in and when the system volts changes. More multiplication of the table in the right spots, but for my testing I kept 15V across the board. My BAP kicks-in at only 3PSI for now (that can be as low as 6g/s fuel flow).

- To get a bit more Inj. PW through the 1400-2800rpm range, can also command/tune a richer AFR.

Anyway, the above has brought my IDC up closer to 30% on low flow. The higher the IDC has gone, the lower the lean spike. No extra PE fuel, and two small humps in VVE from 1600 & 2600rpm. Forgot to mention, I'm also SD/VVE only, MAF de-pinned.

This obviously doesn't help the 1600rpm lean spike as much, due to lower IDC there. Also, this won't do anything to help the low load leanness through these area's, as Inj. PW is so low.

A lot of other settings changed, e.g. fuel-to-wall to 2.0 = quicker transient (in my observation), lower injector off-time (as injector off-time seems closely tied to Inj. Min. PW in GM tunes), and more. Getting the Inj. PW up has had a much bigger effect than anything else. Another note, one log the car was running about 10:1 AFR for some reason, and there were no lean spikes. I didn't check Inj. DC, but I'm assuming it was way up to be running that rich down low.

All this, leads me to believe it may be a problem with the LSA running in this power range (more boost with oversized injectors). Makes sense why not everyone has this problem, you make more power and push your injectors, it seems to go away.

I didn't have this problem running headers, catless, intake, stock injectors, and tune. Only after 2.35" pulley and ID1050X.

Also, i really hope this is all useless, and its just a disable switch for a test we can't see

Disclaimer: Injector delta pressure will obviously be lower with the low flow pressure setting. Watch for any wild oscillations of the Inj. PW, or fuel pressure dropping below 310kPa / 45PSI. I had some of this, but once the openloop DC table was revised, everything smoothed out and behaved. Test with care

[sgod1100]

Hi Guys,

Bit of a long post, but might be of some use to those experiencing this annoying phenomenon with their LSA.

I experience the same lean areas. Tried all the above, and many combinations of disabling/zeroing/maxing/fine tuning random parameters. Don't need to go over that, we all know.

I'm hoping the true fix is a simple disable of some unseen test we can't access yet, but starting to feel its more of a mechanical/inherent problem with the LSA in a certain power range. Stock LSA engine (stock cam), boost/bolt-ons, and oversized (room-to-grow) injectors.

The below isn't a fix of the underlying cause, but did get me to the point of a smooth AFR with no PE rape. This is also only a fix for WOT, also leading me to believe it may not be fixable under light-load until the engine is in a higher power bracket.

- The higher the Inj. PW I could get going through the 1400-2800rpm range, the less of a lean spike. ID1050X on a setup making 600rwhp = only 20-25% IDC, using stock fuel pressure, through the 1400-2800rpm. On a setup making 700+rwhp, I'm sure the IDC would be up.

- Lower the Low Flow Fuel Pressure (ECM 7031) to 310kPa / 45PSI

- Raise the Low Flow Upper Condition (ECM 17020) to a point where changeover to normal flow occurs at a minimum of 2800rpm (raise the Low Flow Lower Condition to match the factory drop for the new upper values). I.E. if your flowing 26g/s fuel at 2800, put 26 in 2800 and lower, keeping above 2800 stock. The g/s will change with fuel need variance, so something high enough to make 2800rpm the minimum in winter/summer etc. I've changed to normal flow at 3200rpm without problem, but unnecessary as the lean event is well over.

- If you're running a BAP, which most will be, I've found altering the Fuel Pump Openloop DC (FSCM 6997) to stabilize oscillating fuel pressure. Very helpful when running the low flow at 45PSI. As system voltage increases, the pump DC is multiplied down. My BAP puts out 17.5V at 3PSI, but the pump DC is being multiplied down by system volts of only 14.8V.

- For ease of testing, I made Fuel System Voltage Min. (ECM 18102) 15V across the board. This gives me 14.8-14.9V in the scanner.

- Calculate the multiplier the ECM/FSCM would apply to the openloop DC if you're BAP volts were system volts. Calculate the difference between your current multiplier (based on system volts), and your BAP multiplier. Multiply the openloop DC table by the difference.

- Example, if your BAP puts out 17.5V, referencing Openloop DC Multi. (FSCM 6998), this would be a multiplier of 0.682 (as far as I'm aware, the system can't see this). If your system volts is 14.8V, a multiplier of 0.8086 is being applied to the openloop DC table. Easiest way to bring the DC values down to where they will line up with system volts multiplier plus BAP multiplier, is multiply the table by the full amount (e.g. 0.682 for 17.5V), remember a number from the table, then restore to stock and multiply the table by the system volts multiplier (e.g. 0.8086 for 14.8V), then multiply the table down again (one try at a time, if the multiplier didn't hit the remembered number, restore back and try a new multiplier). Once you hit the remembered number, copy the multiplier used, restore table to stock, and multiply table by the copied multiplier. For myself, that was a multiplier of 0.84345.

- Now the openloop DC table values have been brought down to where, when they are multiplied by the system volts, the number will represent as if multiplied down by the BAP voltage the system can't see.

- Note: Bringing the pump DC down will cause pump trims to rise, in my case ST trim went from 0.97 to 1.12, LT trim has remained at 1.02 for now. Unsure if the LT will slowly increment, or if the ST is actually trimming DC or it's just a reference of how far it thinks DC is off.

- The DC reduction has smoothed out the fuel pressure oscillations, commanded DC oscillations, and pressure spikes transitioning from low flow > normal flow > high flow.

- I also lowered the Normal Flow pressure (ECM 7033) to 380kPa / 55PSI, just to keep the pressure rises consistent (10PSI jump at a time).

- If you wanted to keep the Fuel System Voltage Minimum stock (i.e. 12.5V > 14.5V based on fuel flow), the above could be applied based on when your BAP kicks-in and when the system volts changes. More multiplication of the table in the right spots, but for my testing I kept 15V across the board. My BAP kicks-in at only 3PSI for now (that can be as low as 6g/s fuel flow).

- To get a bit more Inj. PW through the 1400-2800rpm range, can also command/tune a richer AFR.

Anyway, the above has brought my IDC up closer to 30% on low flow. The higher the IDC has gone, the lower the lean spike. No extra PE fuel, and two small humps in VVE from 1600 & 2600rpm. Forgot to mention, I'm also SD/VVE only, MAF de-pinned.

This obviously doesn't help the 1600rpm lean spike as much, due to lower IDC there. Also, this won't do anything to help the low load leanness through these area's, as Inj. PW is so low.

A lot of other settings changed, e.g. fuel-to-wall to 2.0 = quicker transient (in my observation), lower injector off-time (as injector off-time seems closely tied to Inj. Min. PW in GM tunes), and more. Getting the Inj. PW up has had a much bigger effect than anything else. Another note, one log the car was running about 10:1 AFR for some reason, and there were no lean spikes. I didn't check Inj. DC, but I'm assuming it was way up to be running that rich down low.

All this, leads me to believe it may be a problem with the LSA running in this power range (more boost with oversized injectors). Makes sense why not everyone has this problem, you make more power and push your injectors, it seems to go away.

I didn't have this problem running headers, catless, intake, stock injectors, and tune. Only after 2.35" pulley and ID1050X.

Also, i really hope this is all useless, and its just a disable switch for a test we can't see

Disclaimer: Injector delta pressure will obviously be lower with the low flow pressure setting. Watch for any wild oscillations of the Inj. PW, or fuel pressure dropping below 310kPa / 45PSI. I had some of this, but once the openloop DC table was revised, everything smoothed out and behaved. Test with care

Thanks for the recommendation, appreciate it! I'm actually still on just stock pumps with no BAP and the ID1050s. I am running a blended tune up to 3000rpm. Wonder how these settings will affect being "maf only" above my 3000 rpm set point. I do have a question though, you mentioned "(raise the Low Flow Lower Condition to match the factory drop for the new upper values)" can you elaborate on this. Do you mean to just put the same flow value into that table as well? I checked one of my WOT runs and i'm right around 25 g/s flow at 2800 rpm

[L1FTD]

Ok, no problem! Just wanting to contribute my little bit to see if it helps anyone.

You might even be better off than those running a BAP.

Just forget the part about changing fuel pump openloop DC, yours will be correct stock.

If you want, just try raising the low flow upper limit to a g/s you won?t see until say 2900rpm. If you?re logging inst. fuel flow, just look at a WOT run at 2900rpm. Put that value into 2800 cell and below, leaving the cells above stock. Change low flow lower to suit the raise (5 g/s less than the upper).

This will keep you in low flow fuel pressure until you?re past the lean area. Lower pressure will raise your IDC.

You should see a change for the better in the spike. If it goes well, can try lower the low flow fuel pressure down to 310kPa. This will again raise your IDC through the lean area.

Running MAF, Blended, or SD won?t matter for this. As long as you stay in low flow until after the lean area, won?t matter what airflow calc. is used. If injector data is correct, the system will compensate for the pressure changes and keep fuelling on track, just raises the inj. PW and IDC.

As mentioned before, will only help for WOT. Or may not help you at all? Who knows, but it has helped me out.

Only thing I?m not comfortable with is the injector delta pressure being quite low until I switch to normal flow. Haven?t seen any issues so far, boost hits 14-15psi just after I change to normal.

There are humps at 1600 & 2600rpm in stock LSA VVE. A little valley between 1600 & 3000rpm in stock LSA virtual torque. Dips in the torque model barometric tables at 1600 & 2400-2800rpm.

Seems oversized injectors and boost on an otherwise stock LSA really exacerbate this inherent issue.

Or maybe it?s just a test yet to be disabled? Wish there was a solid answer

[L1FTD]

Sorry, didn?t see the last question.

The factory has the low flow upper set 5g/s higher than the low flow lower.

Just put 26 into 2800rpm and below, in the low flow upper table. Leave above 2800rpm stock.

Copy the upper table, paste into lower table, and subtract 5 off the whole lower table.

This should have you changing to normal flow above 2800, maybe more around 2900. Better a bit further away from lean area, so you can see change. I?ve had it at 3200rpm before but no need.

Give it a test, watch scanner, anything funny going on just pull out. If you see a change for the better, can work on fine tuning it from there

[sgod1100]

Ok, no problem! Just wanting to contribute my little bit to see if it helps anyone.

You might even be better off than those running a BAP.

Just forget the part about changing fuel pump openloop DC, yours will be correct stock.

If you want, just try raising the low flow upper limit to a g/s you won?t see until say 2900rpm. If you?re logging inst. fuel flow, just look at a WOT run at 2900rpm. Put that value into 2800 cell and below, leaving the cells above stock. Change low flow lower to suit the raise (5 g/s less than the upper).

This will keep you in low flow fuel pressure until you?re past the lean area. Lower pressure will raise your IDC.

You should see a change for the better in the spike. If it goes well, can try lower the low flow fuel pressure down to 310kPa. This will again raise your IDC through the lean area.

Running MAF, Blended, or SD won?t matter for this. As long as you stay in low flow until after the lean area, won?t matter what airflow calc. is used. If injector data is correct, the system will compensate for the pressure changes and keep fuelling on track, just raises the inj. PW and IDC.

As mentioned before, will only help for WOT. Or may not help you at all? Who knows, but it has helped me out.

Only thing I?m not comfortable with is the injector delta pressure being quite low until I switch to normal flow. Haven?t seen any issues so far, boost hits 14-15psi just after I change to normal.

There are humps at 1600 & 2600rpm in stock LSA VVE. A little valley between 1600 & 3000rpm in stock LSA virtual torque. Dips in the torque model barometric tables at 1600 & 2400-2800rpm.

Seems oversized injectors and boost on an otherwise stock LSA really exacerbate this inherent issue.

Or maybe it?s just a test yet to be disabled? Wish there was a solid answer

Yeah, this is a pretty simple change to test. This may also help part-throttle PE as well keeping it in low flow longer. Yeah, no matter what I would do when tuning the VVE I always had ridges at 1600 and 2600 (2600 rpm would have a VERY nasty ridge). I'll try it out. When you say "torque model" are you referring to the "air mass based" tables?

[L1FTD]

Yeah, this is a pretty simple change to test. This may also help part-throttle PE as well keeping it in low flow longer. Yeah, no matter what I would do when tuning the VVE I always had ridges at 1600 and 2600 (2600 rpm would have a VERY nasty ridge). I'll try it out. When you say "torque model" are you referring to the "air mass based" tables?

Yeah, pretty quick test. The higher the IDC, the less lean it goes for me. Doesn?t work as good at part-throttle, again due to the lower IDC compared to WOT.

There must be something mechanical or with the tiny LSA cam. Factory VVE has the same ridges but smaller. Factory also has angled injectors, as we know.

Torque tables should be labeled something like ?HiBaro?, ?MidBaro?, LoBaro?, in the torque model section, top left.

They don?t help the leanness, but I can see in the 3D model there are small drops at 1600 & 2400-2800. Same with the virtual torque tables. Just interesting that these specific rpm points pop-up all over the factory LSA tunes.

I?ve even tried running full ZR1 LS9 torque tables, every table changed from LSA to LS9 values. Did nothing for the lean areas, just made the scanner read torque different. Probably would muck up an auto, but I?m M6.

Anyway, if the changes do nothing for you, thanks for trying I think I?ll be over this very soon, and just turn the laptop off

[L1FTD]

Forgot to mention, if you?re going to do the lower fuel pressure, may need to change expected minimum rail pressure.

This is in the engine>fuel>general tab from memory, just below injector flow rates.

Mine had 325kPa minimum stock. Changed it down to 150kPa for this. I believe some tunes have 150kPa minimum stock, and some have the higher value

[sgod1100]

Yeah, pretty quick test. The higher the IDC, the less lean it goes for me. Doesn?t work as good at part-throttle, again due to the lower IDC compared to WOT.

There must be something mechanical or with the tiny LSA cam. Factory VVE has the same ridges but smaller. Factory also has angled injectors, as we know.

Torque tables should be labeled something like ?HiBaro?, ?MidBaro?, LoBaro?, in the torque model section, top left.

They don?t help the leanness, but I can see in the 3D model there are small drops at 1600 & 2400-2800. Same with the virtual torque tables. Just interesting that these specific rpm points pop-up all over the factory LSA tunes.

I?ve even tried running full ZR1 LS9 torque tables, every table changed from LSA to LS9 values. Did nothing for the lean areas, just made the scanner read torque different. Probably would muck up an auto, but I?m M6.

Anyway, if the changes do nothing for you, thanks for trying I think I?ll be over this very soon, and just turn the laptop off

I get it....i've had this issue for like 4 years (after I replaced the stock injectors with some I.D 850s). Ive tried everything under the sun to try and fix it as well. Also, with the help of some guys on here giving other recommendations that I wouldn't have thought of. Sometimes it's just nice to go out for a drive WITHOUT the laptop..lol. Good thing is that even though the lean spots are there I can still go WOT no problem because I haven't had any fueling issues above that 2600 rpm spot

[sgod1100]

Forgot to mention, if you?re going to do the lower fuel pressure, may need to change expected minimum rail pressure.

This is in the engine>fuel>general tab from memory, just below injector flow rates.

Mine had 325kPa minimum stock. Changed it down to 150kPa for this. I believe some tunes have 150kPa minimum stock, and some have the higher value

thanks for the heads up..I just checked and mine is stock at 150 kpa

[L1FTD]

I get it....i've had this issue for like 4 years (after I replaced the stock injectors with some I.D 850s). Ive tried everything under the sun to try and fix it as well. Also, with the help of some guys on here giving other recommendations that I wouldn't have thought of. Sometimes it's just nice to go out for a drive WITHOUT the laptop..lol. Good thing is that even though the lean spots are there I can still go WOT no problem because I haven't had any fueling issues above that 2600 rpm spot

Yeah for sure, that?s crazy, 4yrs fighting this beast. I?m sure many have given up/sold the car/moved onto more power. No solid solution yet. Except more power I guess.

Car feels fine and very nice through the revs. If I never hooked the laptop up wouldn?t even know. Can?t unsee the leanness now, permanently on my brain.

I?m waiting for that moment when I look at a log and it?s rich, having the joy of going in and pulling out the VVE ridges and be done with it.

[sgod1100]

Yeah for sure, that?s crazy, 4yrs fighting this beast. I?m sure many have given up/sold the car/moved onto more power. No solid solution yet. Except more power I guess.

Car feels fine and very nice through the revs. If I never hooked the laptop up wouldn?t even know. Can?t unsee the leanness now, permanently on my brain.

I?m waiting for that moment when I look at a log and it?s rich, having the joy of going in and pulling out the VVE ridges and be done with it.

Yuup, started after the injectors and test pipes went it. I typically keep my toys for a long time so I have no plan on selling the car (bought it back in 2015). Mine is an M6 trans too and I can definitely feel a slight lurch/surge going through the 2600 rpm lean spot during CL. During OL/WOT is when I don't feel anything, but can still see it on my scanner. It would be great if it was a simple check box in the tune...lol...make me very happy

[sgod1100]

Yeah for sure, that?s crazy, 4yrs fighting this beast. I?m sure many have given up/sold the car/moved onto more power. No solid solution yet. Except more power I guess.

Car feels fine and very nice through the revs. If I never hooked the laptop up wouldn?t even know. Can?t unsee the leanness now, permanently on my brain.

I?m waiting for that moment when I look at a log and it?s rich, having the joy of going in and pulling out the VVE ridges and be done with it.

How the hell do you get the fuel pressure to reduce to 45 psi?? I lowered the "low flow" pressure to 45 psi along with the "min pressure" in the fuel control module. Still is stuck at 50psi. Also, when i did a short wot pull the fuel state stays in "low flow" even though the pressure increases to 60psi. It switch to the 60 psi seems to be correct at 25 g/s though. Is it the "regulation pressure" in the fscm that needs to be adjusted? Also, do i just log "control module voltage" under the fscm tab for the voltage that is shown in the columns of the "regulation pressure" table? I'm lost..5:53 is when i did the short pull in 3rd gear.

FP 45 psi and fuel flow changes.hpl

[GHuggins]

Hi Guys,

Bit of a long post, but might be of some use to those experiencing this annoying phenomenon with their LSA.

I experience the same lean areas. Tried all the above, and many combinations of disabling/zeroing/maxing/fine tuning random parameters. Don't need to go over that, we all know.

I'm hoping the true fix is a simple disable of some unseen test we can't access yet, but starting to feel its more of a mechanical/inherent problem with the LSA in a certain power range. Stock LSA engine (stock cam), boost/bolt-ons, and oversized (room-to-grow) injectors.

The below isn't a fix of the underlying cause, but did get me to the point of a smooth AFR with no PE rape. This is also only a fix for WOT, also leading me to believe it may not be fixable under light-load until the engine is in a higher power bracket.

- The higher the Inj. PW I could get going through the 1400-2800rpm range, the less of a lean spike. ID1050X on a setup making 600rwhp = only 20-25% IDC, using stock fuel pressure, through the 1400-2800rpm. On a setup making 700+rwhp, I'm sure the IDC would be up.

- Lower the Low Flow Fuel Pressure (ECM 7031) to 310kPa / 45PSI

- Raise the Low Flow Upper Condition (ECM 17020) to a point where changeover to normal flow occurs at a minimum of 2800rpm (raise the Low Flow Lower Condition to match the factory drop for the new upper values). I.E. if your flowing 26g/s fuel at 2800, put 26 in 2800 and lower, keeping above 2800 stock. The g/s will change with fuel need variance, so something high enough to make 2800rpm the minimum in winter/summer etc. I've changed to normal flow at 3200rpm without problem, but unnecessary as the lean event is well over.

- If you're running a BAP, which most will be, I've found altering the Fuel Pump Openloop DC (FSCM 6997) to stabilize oscillating fuel pressure. Very helpful when running the low flow at 45PSI. As system voltage increases, the pump DC is multiplied down. My BAP puts out 17.5V at 3PSI, but the pump DC is being multiplied down by system volts of only 14.8V.

- For ease of testing, I made Fuel System Voltage Min. (ECM 18102) 15V across the board. This gives me 14.8-14.9V in the scanner.

- Calculate the multiplier the ECM/FSCM would apply to the openloop DC if you're BAP volts were system volts. Calculate the difference between your current multiplier (based on system volts), and your BAP multiplier. Multiply the openloop DC table by the difference.

- Example, if your BAP puts out 17.5V, referencing Openloop DC Multi. (FSCM 6998), this would be a multiplier of 0.682 (as far as I'm aware, the system can't see this). If your system volts is 14.8V, a multiplier of 0.8086 is being applied to the openloop DC table. Easiest way to bring the DC values down to where they will line up with system volts multiplier plus BAP multiplier, is multiply the table by the full amount (e.g. 0.682 for 17.5V), remember a number from the table, then restore to stock and multiply the table by the system volts multiplier (e.g. 0.8086 for 14.8V), then multiply the table down again (one try at a time, if the multiplier didn't hit the remembered number, restore back and try a new multiplier). Once you hit the remembered number, copy the multiplier used, restore table to stock, and multiply table by the copied multiplier. For myself, that was a multiplier of 0.84345.

- Now the openloop DC table values have been brought down to where, when they are multiplied by the system volts, the number will represent as if multiplied down by the BAP voltage the system can't see.

- Note: Bringing the pump DC down will cause pump trims to rise, in my case ST trim went from 0.97 to 1.12, LT trim has remained at 1.02 for now. Unsure if the LT will slowly increment, or if the ST is actually trimming DC or it's just a reference of how far it thinks DC is off.

- The DC reduction has smoothed out the fuel pressure oscillations, commanded DC oscillations, and pressure spikes transitioning from low flow > normal flow > high flow.

- I also lowered the Normal Flow pressure (ECM 7033) to 380kPa / 55PSI, just to keep the pressure rises consistent (10PSI jump at a time).

- If you wanted to keep the Fuel System Voltage Minimum stock (i.e. 12.5V > 14.5V based on fuel flow), the above could be applied based on when your BAP kicks-in and when the system volts changes. More multiplication of the table in the right spots, but for my testing I kept 15V across the board. My BAP kicks-in at only 3PSI for now (that can be as low as 6g/s fuel flow).

- To get a bit more Inj. PW through the 1400-2800rpm range, can also command/tune a richer AFR.

Anyway, the above has brought my IDC up closer to 30% on low flow. The higher the IDC has gone, the lower the lean spike. No extra PE fuel, and two small humps in VVE from 1600 & 2600rpm. Forgot to mention, I'm also SD/VVE only, MAF de-pinned.

This obviously doesn't help the 1600rpm lean spike as much, due to lower IDC there. Also, this won't do anything to help the low load leanness through these area's, as Inj. PW is so low.

A lot of other settings changed, e.g. fuel-to-wall to 2.0 = quicker transient (in my observation), lower injector off-time (as injector off-time seems closely tied to Inj. Min. PW in GM tunes), and more. Getting the Inj. PW up has had a much bigger effect than anything else. Another note, one log the car was running about 10:1 AFR for some reason, and there were no lean spikes. I didn't check Inj. DC, but I'm assuming it was way up to be running that rich down low.

All this, leads me to believe it may be a problem with the LSA running in this power range (more boost with oversized injectors). Makes sense why not everyone has this problem, you make more power and push your injectors, it seems to go away.

I didn't have this problem running headers, catless, intake, stock injectors, and tune. Only after 2.35" pulley and ID1050X.

Also, i really hope this is all useless, and its just a disable switch for a test we can't see

Disclaimer: Injector delta pressure will obviously be lower with the low flow pressure setting. Watch for any wild oscillations of the Inj. PW, or fuel pressure dropping below 310kPa / 45PSI. I had some of this, but once the openloop DC table was revised, everything smoothed out and behaved. Test with care

I can see definitive merit with this. I would recommend playing with injection timing to further help things possibly. Maybe Steve could give you his injection table for further testing?

I have used this same method on big cam builds to increase pw's and smooth out drivability so I know this could help. Sometimes night and day better just from lowering rail pressure.

You might need to post your tune or email it to one of the guys to show the details of what was done. Good work!

[L1FTD]

How the hell do you get the fuel pressure to reduce to 45 psi?? I lowered the "low flow" pressure to 45 psi along with the "min pressure" in the fuel control module. Still is stuck at 50psi. Also, when i did a short wot pull the fuel state stays in "low flow" even though the pressure increases to 60psi. It switch to the 60 psi seems to be correct at 25 g/s though. Is it the "regulation pressure" in the fscm that needs to be adjusted? Also, do i just log "control module voltage" under the fscm tab for the voltage that is shown in the columns of the "regulation pressure" table? I'm lost..5:53 is when i did the short pull in 3rd gear.

FP 45 psi and fuel flow changes.hpl

Ok, had a quick look at log. Definitely the same spike as me.

In the log, your hitting 28g/s fuel flow around 2850rpm. You're switching to normal flow around the 25-26g/s I suggested, but that's still too soon in this log.

Try setting low flow upper to 29g/s in 2800rpm and all the cells below make say 34g/s, above 2800rpm can stay stock. Change the low flow lower to match the 5g/s drop as mentioned before. Takes a bit of fine tuning to pick your spot when you want it to switch. If you make the cells below 2800rpm a high number, in winter/summer/all conditions the change to normal flow won't happen until 2800rpm or more. Same goes for cells above 2800rpm, if they're a lower number (like stock values), then as you pass 2800rpm the fuel requirement for the switch becomes less. Helpful in summer, and keeps everything centered around the 2800-2900rpm.

If want to switch even later, just look at your logs and work out how high you need the values before the switch, and how low you need the values after the rpm you want to switch. Basically choose an rpm, check multiple logs for fuel flow at that rpm, make numbers high before the rpm you want, and numbers low after rpm you want.

Also, majority of my tests are done in 4th gear, and WOT anywhere from 1200-2000rpm. Feel sorry for the clutch and engine, but really helps to see the lean spots and switching when they're unaffected by transient.

Unsure if 3rd gear WOT would have vastly different fuel flow, but just check your logs and choose a fuel flow and rpm above 2800.

Forgot to mention as well, I changed my Hot Fuel Soak and Hot Fuel Pressure to match the lower pressure.

Screenshots of all that's needed for the fuel switching and pressure, and also my openloop DC.
Screenshot (4).png

[L1FTD]

Screenshot (2).pngScreenshot (3).pngScreenshot (1).png

[L1FTD]

I can see definitive merit with this. I would recommend playing with injection timing to further help things possibly. Maybe Steve could give you his injection table for further testing?

I have used this same method on big cam builds to increase pw's and smooth out drivability so I know this could help. Sometimes night and day better just from lowering rail pressure.

You might need to post your tune or email it to one of the guys to show the details of what was done. Good work!

Interesting how, for me at least, just a few extra % IDC can shrink the lean spot down.

On a few logs, I?ve seen the surrounding areas go a tad rich. I think I pulled a bit out of the VVE peaks and smoothed the transition into and after the peaks.

Did another log tonight at 45psi, and 2000-3000rpm WOT nice and smooth, maintaining commanded PE.

No help for the part-throttle 2000-3000, still lean as before. I think I?d have to be running pretty low fuel pressure to clean up the part-throttle PE EQ error, and no chance in closed loop (although I don?t notice this much).

GHuggins, I?m sure you?d be knowledgeable on this. 45psi with 10-15psi boost leaves a pretty poor 35-30psi delta pressure. Have you run them this low, or gone lower?