I have been running what i thought was stock GM SA table. obtained on CF forum. it probably is. anyway like some others i am getting that surge when under low load(all gears) at low rpms. typically when creaping through a parking lot in first of 5(manual trans) it is worse. my BLM's were running 128-136 in those cells in that bin. the SA cells show 15 degress advance in all cells this occurrs. i had changed it from stock values to 15. i think i had 400-1800 rpms and 20 map to 50 map accross the board at 15A. using PE adder and i wanna say total adv for PE is about 35A. so had the surge but not terribly bad. so i enrichened the cells that were lean and burned a new chip with 21 deg in those cells to see the effect 15 vs 21A. and result was noticable more surge. pretty bad. i am confused as to why 21 deg would cause the worsening? the surge i believe was spark related. also maybe i should not have done this but i also ran OL disabiing CL( for first time) when i ran 21 A. now a mechanical adv never runs that much timing(15-21) to best of my knowledge in that area 20-50 MAP. it was said we do that cause we can in CC cars. i could be wrong on that. i have seen so many SA tables that have 21 or greater in those cells. would you suggest i burn another say 10 deg(20-50) and try that? anyone wanna post a table that may work better?

 

Might want to hook a wideband up and see what the AFR is doing. Fluctuating AFR will cause a surge. Lots of causes for that. Also may want to make sure the timing isnt chaning abruptly in the areas that your cruising in.

 

wide band was hooked up until 3 weeks ago the 02 sensor took a dump? new one going in tomorrow. thank you UPS. i dont think i saw fluctuating A/F since steady throttle and those cells for BLM are pretty close or were until the temps fell from 90F to 65-70F then they all skewed lean BUT that was corrected in the 21A burn.

my pulse at idle may have another reason. going asynch due to injector size too large is my best guess. that and IAC too happy so burned a OL chip and that did not help all that much. i am inclined to disable IAC just for a test to see what is up.

but back to Q why does one run in excess to 20 A at rpm/mph where there is no load on engine?

gas mileage possibly? but the 1900 rpm 66 mph range runs great as engine has somewhat of a load. if i run 5th gear at 50-55 i get surge and especially with cruise.

any reason i should NOT run 10 deg A in that above mentioned area?

 

Theres not much cylinder pressure and the leaner mixture will take longer to burn. Those two things mean youll need more timing for the motor to run properly. What exactly is the sync BPW at idle/low load?

 

BPW ? i cant get tunerpro rt 4.0 to datalog. see my other post on no go.

winaldl does show asynch occasionally however?.

that brings up a posible related issue. as you may be aware i have been trying to remove a lean spike in AE as seen in seat of pants and on WB datalog. i improved it my adding much larger # in AE TPS at % 0-3-6-9-12. in fact i have same usec for 0-3-6. like 305-305-305-366-427 and so on. that helped. seems when TB cracks open it can flow air yet PS is slow in coming but arrives. if i open throttle ever so slowly i can make the lean spike longer in duration. if i accellerate briskly no prolems with drivability. it just goes. also over 2000 rpms and AE it just goes. i am thinking it may be due to throttle blades blocking off the fuel temporarily. once they open 20% or so the fuel is sheared off. and velocity is minimal. my buddy that drag races his BB buick notes that when we blip the throttle it is like engine is slow to respond to PS. like it coughs yet no lean pop. if i bring to 1500 and give it AE it seems more normal comparing to a carb. is the all of above plausible?

 

That to me says VE is low for that kpa region.
Give it a little more throttle and either AE is covering it or
the higher kpa VE region is closer.
If it was a AE problem, then the lean spike would be lower/shorter with less delta TPS.

 

my wide band was functioning today. i need to calibrate it but it appears i am in fact lean on those main fuel tables. per the 20 minute run today. i was trying not to invoke AE and it does show A/F 15-17/1 maybe 18/1 occasionally. also the A/F is very unstable. i will assume i am moving accross cells and some are leaner than others. now this is running OL. so if my tune is lean CL cannot enrichen to magic 14.7. looks like i will log some and fatten up those tables 20-55 MAP and 400-2400 rpms. i was thinking the SA was affecting it. will returnn to the stock GM SA as well. yup i bet lean.... thanks.

 

The calibration in the ecm for the closed loop PID could also be off. Are the AFRs fluctuating up and down?

 

explain PID? i missed that somewhere.

on the WB i had stable A/F more or less until i upped the FP from 13 to 17 and then some issues arose with more rpm pulsation at idle and low speed drivabiltiy under no load. i have not tuned for three weeks as car in body shop(shiny red) and then my mechanic had for a week fixing oil leaks. plus WB sensor was killed by paint fumes so did not do any logging till today. i ran a few AE experiments and found it needed a large dose of AE just at tip in but today burned a chip with more fuel VE(5%) tables as was lean 400-2400 rpms and 20-50 map. seems i can get enough gas in engine. my NB may be off on calibration as i will assume 14.7 on NB is showing 15-16/1 on WB. i am OL now so will tune VE with WB.