So the short of it all is i recently traded in my tired L03 for a pro built 5.7L 350 sb, edelbrock heads, headers, mainfold, water pump, comp 218/224deg 112lsa cam shaft, aluminum roller rockers, 3" cat, 3" cat back, flowmasters, . . . all the goodies, sittin on top the turbo city TBI unit.

After 2 custom burned proms (from datalogs), a prominator (in the end), a dozen VE fixes to lean the VE table out -- due to cams lsa pulling less vacuum, and endless reading of these posts. I am thankful to say i finally have it dialed in . . . mostly.

One consistent stall still mocks me . . .
Its predictable . . . engine starts nicely, rpms hit about 1400 then settle back down to 800, closed loop mode kicks in . . . the engine then starts to surge between 800-1100, as i watch the IAC count go from the 50's down through 40's -30's. . . all the numbers, till it hits eventually hits 0. Engine stalls. Takes about 3 minutes for this to happen while it surges itself to sleep.

a moment later, i start it back up . . .starts fine, RPM's hit 1200, settle back down to 850, closed loop kicks in 30 secs after ignition, surging starts again . . . iac counts drop from 60, but never hit 0 -- usually sit right around 8, idle stablizlies between 800-900 and will idle fine . . . no problems, steady as she goes, sounds great , no surging, purrrrrrrr. . . 128's across the board. . .
and i have no clue

 

Might need to work on the IAC park posistion, and/or the choke AF/ timer decay rates.

If the *choke* AFR/ timer rates don't match the warming-up commanded idle speeds, then the IAC kinda wanders around.

The IAC movements can be a royal pain.

Some codes allow for timing changes based on idle speed errors, they can be a blessing, and sometime haunt you. If you have them then you just have another element to balance out.

 

Quote: a dozen VE fixes to lean the VE table out -- due to cams lsa pulling less vacuum, and endless reading of these posts. I am thankful to say i finally have it dialed in . . . mostly.

please explain. how can adjusting the VE tables help with fact of less vacuum? would not the 02 just override the fuel tables and enrichen(BLM/INT correction) as it (02)sees a false(?) lean condition? if using a map sensor i can not see how fuel tables can override? assumes CL. what am i missing? i may be in error. i would think the fix on the less vac issue is run open loop at idle and off idle in those cells. i have cam going in next week(i have said that more than once) and will be watching my tune as it will as was first run on new cam. even with my old cam 206/216 @.05 it appears i am adjusting the fuel tables in those ide areas and the blms just stay rich (CL). i continue to take away fuel to little avail. seems anyway. lthe above pertains to TBI/speed density cars.

 

It could be a combination of all these closed loops acting together, but my guess is there is a steep point near idle in the VE table. The steep point will richen it when hit, the engine will rev out of that point from the small rich power surge, the closed loop will pull out fuel, and a viscous oscillation starts. IAC is doing its best, but the lag involved in that puts its movement in at just the wrong time. Spark is faster, but it can't do much about the mixture.
I'd attack it by first disconnecting the IAC. Then calibrate VE at idle in park, then put it in gear and calibrate. If closed loop is causing a problem, set the min and max integrator to 128 and get it calibrated in both areas before turning it back on. Then calibrate the free rev areas just above idle (where it's oscillating to and from). And then try adding in closed loop fuel, then get the IAC going again. Spark shouldn't cause the oscillation, so leave that functioning.

It could also just be oscillating about a Block Learn Boundary, causing one block to go up while the other goes down (it's a lag issue). If you see that, you could try moving the boundaries out of the way.

Good luck.

 

The ecm does an entire routine to figure out the PW. Until, closed loop, the O2 is ignored.

Once in closed loop, the ecm can slightly adjust the PW, based on feedback from the O2.

 

The idle speed varing, can cause a spark correction to be applied, and that can make matters more complicated when trying to iron a problem. So 0'ing out the idle speed timing corrections, can be handy. Obviously this just applies to code that supports an idle speed spark correction strategy.

 

Im quite new to all this . . . but this was my understanding of traxions tuning article

"Camshafts have the biggest affect on VE (as compared to other naturally aspirated modifications). The VE curves for this setup will change for several reasons. The obvious reason is that this cam’s higher duration numbers and lower LSA numbers will make this motor less efficient at the lower RPMs but more efficient at the higher RPMs (very general statement for the purposes of explanation). However, one of the biggest effects here is that bigger cams (especially those with tighter LSAs) will pull much less vacuum at idle (higher kPa). Less manifold vacuum means less vacuum to those devices that are connected to manifold vacuum. The fuel pressure regulator is controlled by manifold vacuum. More ‘pull’ (more vacuum, smaller kPa) on the regulator reduces the effective fuel pressure. Less ‘pull’ (less vacuum, higher kPa) at the regulator increases the effective fuel pressure. Thus, if we install a cam that pulls less vacuum at idle then the Fuel Pressure Regulator will see less vacuum and the overall fuel pressure will be greater. This results in a very rich condition at idle. The bigger the cam duration (with LSA and lift remaining the same), the less manifold vacuum at idle. The overall response here is to re-map the lower VE table to supply less fuel at those RPMs and kPa values where the car idles. We will have to decrease those VE values."

 

Nah, the fuel pressure doesn't actually change across the injector. That's what the vacuum reference line does. It keeps the pressure difference from the fuel line to the intake manifold constant. That's why when the vacuum is high, the pressure is low - there's still 44 psi across the injector, just 34 in the line, and essentially (gauge) -10 in the manifold. That differential is what determines the injector flow rate.

It's a common misconception, and is a little tricky to understand, so don't feel bad, especially since you've read it from a somewhat reputable source. The newest cars are doing away with it for several reasons, including lag response, fewer components = lower cost, more powerful control algorithms (controlling fuel pump voltage - keep recirculation down to keep gas tank cool (vapor canister emissions) from engine bay heat being added to the fuel (not from being compressed - its a liquid and doesn't heat from compression - it's incompressible!)). They are compensating for it with pulsewidth changes and such (sequential give way more dynamic range - just like single fire mode, but without the emissions penalty of spraying on an open valve).