396V8

hi all

i did an cam swap from a 226/228 to a 236/240 on this engine
415ci, 195 AFR comp port heads, single plane efi

i inserted the distributor in the way it was before (dead straight) and tried to fire the engine with open headers......

when i turned the key....it cranked...and bam...started...like there is no inertia in the engine...
it felt like the engine turned up from cranking to idle in 2 strokes...

i mounted the exhaust, and controlled timing....around 40°....way too much..

setted the distributor to 27°, thats what is in my closed TPS SA table...

when i start the engine now, its like cranking, then a few cylinder ignite, the next comes in, finally i have idle...no more "bam" starts...

the engine have good power, although i feel theres more in it, its running on the old tune now
also feel, that the exhaust is holding me back

of course, i have to play with idle mixture, aso, but is there a way to tune for such "bam" start ups?

thank you

884+3

You have to remove the ECM from the loop when you're setting the base timing. Look for a brown wire with a black stripe and seperate the connector provided and set the timing to the value shown in your bin. Ignore the SA values, look for the base timing value witch is 6* factory setting. There is a possibility the outer hub of the balancer rotated skewing your base timing setting.

JP86SS

iTrader: (1)

The IAC PARK position can help the start.
Opening farther (more steps) can ease the cranking effort on the starter.
There are "warm" park positions also so restarting can be adjusted.
By adding the exhaust the pressure differential went down and you probably are moving less air. Opening the TB to your best idle operating position (with minimal steps on IAC when running) and then going back to the park position setting should yield better results.

396V8

Hi

The balancer is a brand new ATI sumper damper...

i know that you must set timing with the EST disconnected to 6° mechanical, thats what is set in the ECM, so mech timing and ECM timing are consistent

but theres another method, too, especially for engines with bigger cams that dont like idling at 6°

you set all values in the "Closed throttle Spark Adv" table to the value you like...im my case 27°

then you adjust the distributor so, that it shows 27°...so mech and ECM timing are consistent

hope i dont make a mistake here, but i dont see one...

sailtexas186548

iTrader: (2)

if all you did was retard the timing mechanically, and you like how it started and idled before, just advance your start/idle timing electronically and it should start like it used to

396V8

hi

i´m with you, but i had around 40° at idle...thats a bit much, i think...

another thing...when does the ECM take control of Timing? different stories are heard here....

i read somewhere, that until 300rpm or so, only the Distributor controls Timing and ist started with 6°, then they ECM takes over--

but that would explain, why it started that way, when it was mech adv so much...

so, when i advance the Distributor, lets say 12°, and set the constant in the ECM also to 12°, then everything should be in line for the ECM, but from a mechanical adv standpoint i should have 12 instead of 6°

i will try this next Weekend....

RBob

iTrader: (1)

You are correct, the ECM doesn't take over the spark advance until the RPM is over 300. This is true for AXCN, other calibrations can have it set differently.

With the engine cranking at the base setting, make it higher (as you suggested). I was going to say 10* BTDC, but trying 12* BTDC won't hurt. Don't forget to change the calibration to match.

RBob.

396V8

Hi RBob

thank you for the confirmation

i checked my .bin (ARFP) and its also 300rpm

i will try and set it to 12°, match this in the .bin and repost the result here

thank you

gta324

Similar to my setup....

Will follow this one But I cant remember how mine starts up except that I tried to raise my timing but for some reason I put it back to 6-8deg.

I know I had a problem with it cranking to slow/heavy...

anyway I played alot with my crank PW, and BPW vs ref.pulses. and then I was satisfied (for the moment)

ps would be nice to see your SA table when you have tuned it, I think I have little to high EGT's on mine and will try to tune some more this summer.

/N.

396V8

ok gentlemen, weather was fine enough to test the new .bin in the car...


i set the initial spark adv to 12° and also adjusted the distributor to match it,
started the car (1990 corvette, manual six) cold, engine cought, tried to run and died.

started again, runs, goes down to stall saver, then idles fine

Made did a short test drive, and although the engine runs very rich, BLM 108 most of the time-tune is off, of course, driveability was relatively good.
i also adjusted the prop step size gain vs airflow and the prop step size vs error and also the closed loop fuel integrator delay vs airflow for my LT headers
in terms of cam surge, these adjustments seems to help greatly, but of course more needs to be done here

after hot sitting for a while, i tried to start, engine doenst want to fire up...but with a very slight step on the gas....i got the "flare up" start the i wanted...so a bit more air helps
is there a possibility to check, if the engine is diing from too much or too less fuel, other than reworking the .bin?
if so, i have an ostrich, so its rather easy

so, is it possible, that my IAC, better, the IAC housing is maxed out...?

also set the IAC park position to 220 counts, but it stays at 180..i assume, this are the max throttle follower steps..dont know, why this is used here

if so, i can open all the way that i want, when the area of the air is limited by other factors, i can do what i want, i just wont flow more...i will check this, and let you know-if so i will machine it, that it works ok....

i will check for this, but i think its a possibility..had it idling a good time
the iac counts went down from about 112 to 40 with little to no change in rpm and map, all with engine hot

next thing, i get some (false)knock counts, maybe the shaft rocker system is triggering it, although its very quiet, or its coming from being overly rich...i can hear the crackling noises in the exhaust, maybe from the still burning mixture in the tubes


i have so many questions right now, that i dont know where to start...

so let me make an conclusion what my problems are now

*engine dies at first start
*idle takes long to settle after coming to a full stop
*possible false knock counts

one more thing, is there such a table in TC, that can define fuel delivery while cranking?
i found crank fuel delivery delay vs mat...i assume, the fuel delivery starts, after a number of ref pulses happened...so the engine can speed up, than fuel is injected, maybe this helps a defined start, when the engine pumps fresh air first before fuel is added...especially after sitting...
there are some crank fueling tables in the .bin, maybe a good starting point also, but first thing is, to get the IAC in line

i learned a lot here, and i hope i will learn a lot more, would be nice to get interesting answers...

if anybody wants to take a look at my. bin and logfile, i would be more then happy

thank you

RBob

iTrader: (1)

See if this parameter allows for more IAC steps:

L866A: FCB 160 ; MAX STEP MOTOR POSITION

For more IAC steps while cranking see if this table works:

For cranking fuel there are several tables that can be changed. Can work with either/both the cranking PW versus CTS and the cranking PW versus DRP.

RBob.

396V8

Hi RBob, and thank you first...

may i ask you one principal thing...

the IAC opening is measured in steps...max steps in the ECM are 255

just for interest, i tried to run the IAC on a stepper motor controller, where you can adjust all the parameters you want...

guess what, at 255 steps, the IAC pintle is just maxed out...the motor continues to run, but there some kind of torque limiting clutch built in in the IAC (or my IAC is going south, will get a new soon anyway)

in fact, the IAC cannot take more than 160 or sth steps (from the stepper motor driver) in total from fully open to fully closed position

ECM logic says, to run the pintle to the seat when starting, for a zero baseline.

thats defined as zero steps

when the valve then opens too much, lets say, 180 steps, but the pintle moves only 160, 20 steps are lost in the "torque limiter"

if you close the valve now lets assume 50 steps, the ECM counts from the 180, but in fact, max open is 160...so you yield 110 steps instead of 130

if this is true, its extremely important to limit the counts to max. possible pintle movement for an accurate function

this all leads to the final question:

are 255 steps from the ECM the same as 255 steps from the stepper motor driver?

or are this half steps?

would be interesting to know, maybe this shed even more light on IAC function

greeetings

Update:

one full pintle movement fully closed to fully open are 130 full steps! (one step equals 15° motor movement, threading is about 1mm/revolution)

so, maybe in the ECM are half steps, that would come in line with the way the pintle can travel...

RBob

iTrader: (1)

Is this with a stock GM TB & IAC, or an aftermarket piece? That can make a difference in the total travel of the IAC.

When the IAC is at the end of travel the motor sorta' stalls. It will click, but that is it moving a little then stalling.

Depending upon the code the ECM resets the IAC in different ways. In the '7730, $8D (and many of the C3 TBI ECMs), at key off the ECM tells the IAC logic that it is at a high number of steps (say 200, which will bottom the (pintle into the orifice).

The IAC is then commanded to 0 steps, and when reached is then commanded to the park position. At key-on the ECM knows that the IAC is at the park position.

Yes, that would occur.

A step in the ECM is a step at the IAC.

RBob.

396V8

Hi RBob

thank you!

this was all done with a stock GM TB & IAC, i cnc´ed a housing myself with larger air passages, but still the exact dimension of the orifice and the air guiding housing
thats what i also noticed, clicking, when the pintle is at the end of its travel.

i will hook it up to the car tomorrow, and will try some various step numbers, then we can make sure what a step is in mm of pintle movement...

greetings

396V8

hi all

IAC step update:

i set the IAC steps to 180, that yields a pintle movement of around 8mm
thats about the maximum the IAC can travel, more steps wouldnt move further, the orifice is fully open

i opened the throttle blades a bit, just so that the IAC can still take control, and the startup is a lot better now...no more stalling when starting cold, also warm startup is better, but heres more room for improvement...


can someone shed light on this table?

"crank fuel delivery delay vs MAT"

i thought, that the fuel delivery starts, after a number of DRP happened..
in reality, the engine starts immediately with the turn of the key...no delay at all...this seems to occur, when the engine is warmed up.

i set all values to 6 in the .bin, because i thought to get the engine rotating, then switch on fuel for a more defined start up

thank you

396V8

Hi all

i want to give you an update on the start up behavior

finally, i have the things straighted out

Here is what i did

1) and most important..i made an IAC housing myself with really big air passages, so that thy have the same area like the air holes in TB

2) set the initial timing timing to 12°, of course matched this in the .bin
3) closed TPS SA 25°
4) increased crank fuel PW vs coolant temp
5) increased start up enrichment vs coolant temp
here was a WbO2 very helpful...i fed it from an external 12v source and found this
when starting, im around 14:1, then it leaned out quickly 20:1 and fighted with stalling, which it also did most of the time...point 5 solved that

this all give me a nice solid start up, no more flare and die...

thank you

RBob

iTrader: (1)

Interesting about the IAC, it seems as thought he engine doesn't pull a lot of vacuum. So requires a larger opening.

Thanks for the update, I'm sure it will help others.

RBob.

396V8

Hi RBob

i think, a Forum should be like this...get help from other, and help others..

i forgot to mention, i also upped IAC Counts to 180...more dont make sense, as the IAC is just maxed out

in fact, the engine does pull good vacuum, not like a stocker, but still good..

also fact, i have an 58mm TB, and the bores for the IAC are sth like 1/2 to 5/8"..

the stock IAC housing have very small passages, metric i would say like 5 x 10 mm for the air pathes....so, the IAC can open what it wont, the restriction is the housing....

just some more Food for thoughts :-)