MAF Timing LB7

[LB72004]

I myslef personally do not see any reason as to why you would need to change this. It is pretty easy to set up a timing table to allow for good milage(high timing in the cruise area), and then set it up for fast turbo spool(moderate timing in teh low RPM power areas). I just don't see any advantage to setting it up so as to change timing tables based on MAF flow. I know I have played quite a bit with timing, and found with the LB7's larger injectors they don't take as well to really high timing at lower RPM's like the LLY+ does(I saw a drop in milage at more than about 6.5 degrees of cruise timing whereas the LLY guys will go up to around 8-10 at cruise). And I have found that a little more timing over stock helped my spool up some. Also just because the option is there to change timing, it doesn't mean the rest of teh code in the ECM will fully support the changes. There is alot in the ECM we cannot see, so like you posted above there could very well be some other hidden tables that need to be opened up to get this to work. Then again, if they open the tables who is to say it will be beneficial. I know i for one like teh MAP based timing as I have been up in altitude ab it and found it to work quite nice with the changed timing at altitude.

thanks for the reply. that makes sense. that's pretty much how i have had my timing when on MAP. with no real data other then how it feels, it seems that when i lower the timing i get faster spooling. let say i am cruising down the highway at 2000 RPMs and 20 MM3. now if i wanted to pass someone driving slow then i press on the accelerator. in a second or two the turbo spools up and i get the power to pass. now if i lower the timing in the higher MM3 areas of the 2000+ RPM band it may spool in one second or less creating a more responsive truck (which is more fun to drive). now lets say i am towing and the RPMs are sitting in the 2000+ range and timing is set too low (for quick spool) then the MPGs go out the window and the EGT go through the roof.

now i know there is a line between the two where one can get both to work, i was just hoping that this would produce a better system.

it doesn't mean the rest of teh code in the ECM will fully support the changes.

i was kind if hoping this wasn't the case. if it is, wouldn't one think that this option would not be available? but what do i know? i not a programmer. i guess the EFI live programmers (Ross???) would be the only ones to be able to confirm this

and another question... when the timing is based on the MAP (baro) sensor is it only set on startup or is the ECM constantly monitoring the sensor and adjusting as necessary? example: driving from low altitude to a high altitude, the ECM would start out using timing table C but as one climbed up the mountain would the ECM switch over to the other tables B or A? or would this only happen if the engine was restarted. and what about the reverse? coming down from a high altitude, would the ECM still use table A/B until the engine was shut off?

i know that this may not help get the problem resolved but if(or when) i end up going back to MAP timing then it would be nice to know that the ECM is taking care of the baro timing selection properly

[THEFERMANATOR]

As I understand it, the ecm monitors altitude constantly. Also I believe it will sort of smooth the 3 tables together as it goes up in altitude. I know I started out at around 2K feet of elevation and went up just over 6K, and the transition was smooth and seemless as I went up and down in elevation.

[LB72004]

As I understand it, the ecm monitors altitude constantly. Also I believe it will sort of smooth the 3 tables together as it goes up in altitude. I know I started out at around 2K feet of elevation and went up just over 6K, and the transition was smooth and seemless as I went up and down in elevation.

thats good to know. i thought that i read somewhere that the ECM only checks it at startup, but maybe that was for trouble codes only

[LB72004]

here is a wiled thought. if the programming was never completed for the MAF timing, could one swap the baro and boost sensors and use that. B0905/6/7 go up to just past 148 PSI, just dont know if the sensor will go up high enough. dont think i would ever do it though

[LB72004]

i guess i am eating my own words, ok, so i ran some small vacuum line to a tee that i put on the boost sensor tubing and connected it to the baro sensor. adjusted the B0905/6/7 based on data from the previous logs. well it worked... sort of. the transition from one timing table to the next is so slow that it would be worthless to set up this way. makes sense as GM knows that one doesn't just drive from sea level to 8000 ft in one second. so there is probably a hidden table that determines how quickly it will switch from one table to the next.

at least i know know that the baro sensor will read up to 29.73 PSI, which is plenty for what i was trying to do. oh well, back to conventional timing.

i may still give the boost switch or DSP output wired to the DSP5 wires a try, will let you know if i do.

[LB72004]

i wired in my boost switch to my DSP switch (it is a 6 position so i wired it to #6) when i have it set to position #6 the ECM sees it as DSP#3, when the boost goes up it automatically goes to DSP#4. right now the boost switch is set a bit to high and would like it to come on sooner, but it works. have to play around some with the debounce and PSI setting. i think i want to wire it up to the DSP output so i can change the boost level to which it will change tunes. need to do some logging and tweaking so see how it runs, MPG, Etc.

[LB72004]

i wired in my boost switch to my DSP switch (it is a 6 position so i wired it to #6) when i have it set to position #6 the ECM sees it as DSP#3, when the boost goes up it automatically goes to DSP#4. right now the boost switch is set a bit to high and would like it to come on sooner, but it works. have to play around some with the debounce and PSI setting. i think i want to wire it up to the DSP output so i can change the boost level to which it will change tunes. need to do some logging and tweaking so see how it runs, MPG, Etc.

well it seems that from a stand still and then flooring it my old timing (dsp#0, 1 or 2) was just as fast and responsive. but when it comes to the "passing gear" or driving 30+ MPH and pressing the accelerator hard, the boost-switch-wired-to-my-DSP 3 & 4 was more responsive and picked up more quickly (better).

i think i am going to wire my setup into my DSP output so i can program the boost level that it will switch timing tables. this should be more stable and make it easier to make changes the level at which it changes the tuns.

[LB72004]

update.

i managed to find a good high quality boost switch to use as the DSP output was not working properly. i have it wired so when it is in DSP #3 and the boost increases to about 22 PSI it automatically switches to DSP #4.

from a stand still and pressing the accelerator down pretty hard it would puff a small cloud and then would be spooled and would take off quite quickly. it also seems to work well while cruising and then going WOT. this is better results then what i posted earlier.

the tuning that i have been running would hardly ever smoke but produced good power. now it will puff a little bit when you get on it, but it spools up fast and clears right up.

i have done some logging and when cruising at 50 mph and then suddenly pressing the accelerator to 90% the boost would go from 15lbs (no boost) to 36 lbs (full boost) in 1.8 - 2 sec. this is about 0.2 seconds faster then my previous times.

i dont have any logs yet of of boost times from a dead stop but will test it soon.

so far it feels good. i think i will run this for awhile and see how it performs

Jason