Ugly looking start-up - What's the cure?
 

My O2s go from real lean for 13 seconds to very rich for 25 seconds. During this whole time, it is adding lots of STIT (over 2 add some points). Then the O2s start to cycle a bit and all of a sudden the STIT starts falling fast. By the 1 minute mark, the STIT is .5 negative. By 176* it is telling me that it only wants 6.7 g/sec airflow which seems low.
:bang:

mods: heads, 228/224 113 cam, 1 7/8" headers, FAST 90mm TB


I've reduced proportional fuel at idle and used the effective area to 48%. Car drives much better since those changes, but cold start up is much worse.

HPT log attached

TIA :)

Joel, you probably need to go into Open Loop Fueling table (ECT vs. MAP) and lean it out in the tables that are giving you trouble. I copied an Ausie Table from a Holden that was speed density tuned. My open loop startups are much less stinky and a lot more smooth.

I've done that in cold start-up area (MAP 45 - 60, 68* and below) where the multiplier gets real high, but haven't touched the warmer areas. This was a warm start-up since the ECT was about 100*. I also reduced the cranking VE by 8% since it was so much higher than my normal VE (which was reduced by double digits in that range). I also reduced the length of Afterstart Enrichment delay in the 68* - 133* range to lean out the start-up idle. Maybe the combination of the cranking adjustment & afterstart are too much and I've overly leaned it out?

Where are your idle airflow tables?

temp...RAF
32.....16.5
68.....13.5
104....11.7
140....10.8
176....8.5
212....7.5

I have raised them up a bit, maybe they should be lowered.

The car is an M6 with an Al. flywheel

The car is just really stumbling during start-up. Before the IAC effective area change, the car would fire up very nicely.

I think changing the IAC effective area to 48% was a mistake. The IAC needs to be a lot more aggressive than that. Basically, when running a 90mm TB, you still want your curve to be fairly steep at first (to handle cold starts and a/c), but then flattening out more once you get past 100 count. I built my own table and it works well with the Nick Williams 90mm TB. If you're running a FAST or TPIS TB, you may need a different curve, but trust me, it will be closer to the stock table than it will 48% of it.

Patrick :
I tried 60% and that seems to work, but after reading Phil's post about the FAST 90mm TB, I went to 48%. I can put it back to 60% as the car still drove much better than stock.


What do you do to build the IAC table?

Basically, I logged my IAC counts and compared them to the relationship between my desired IAC airflow and my dynamic (calculated) airflow. I made sure that desired airflow and dynamic airflow matched at all temps regardless of whether the a/c was on or not. Here's what my table looks like:

IAC Effective area (IAC Steps)
Square mm, Value
0.0 0
2.0 0
4.0 0
6.0 0
8.0 0.000000
10.0 0.000000
12.0 0.000000
14.0 0.000000
16.0 0.000000
18.0 0.000000
20.0 0.000000
22.0 0.000000
24.0 0.000000
26.0 0.000000
28.0 1.000000
30.0 15.000000
32.0 25.000000
34.0 50.000000
36.0 70.000000
38.0 90.000000
40.0 110.000000
42.0 125.000000
44.0 135.000000
46.0 140.000000
48.0 145.000000
50.0 150.000000
52.0 153.000000
54.0 156.000000
56.0 157.000000
58.0 158.000000
60.0 159.000000
62.0 161.000000
64.0 162.000000
66.0 163.000000
68.0 165.000000
70.0 167.000000
72.0 170.000000
74.0 173.000000
76.0 175.000000
78.0 178.000000
80.0 180.000000
82.0 181.000000
84.0 183.000000
86.0 183.000000
88.0 185.000000
90.0 187.000000
92.0 190.000000
94.0 194.000000
96.0 199.000000
98.0 205.000000
100.0 210.000000
102.0 215.000000
104.0 220.000000
106.0 227.000000
108.0 232.000000
110.0 238.000000
112.0 245.000000
114.0 252.000000
116.0 260.000000
118.0 264.000000
120.0 267.000000

Sorry for the vertical format. It's an EFI Live thing.;)

I'd reduce the Cranking VE by the same % diff between your stock and New VE table. Helped mine alot...especially hot starts. I'm Open Loop/SD. FWIW.

i had troubles starting, i changed a LOT!

start up enrichemnt
friction airflow
olfa
spark correction
cranking ve
effective area
idle airflow

those are the main thing i had to do to get it inline. you using hp tuners? if so send me your tune to budchevy358@yahoo.com and i can try to give you a hand. i fougth this for the longest time and this is the best solution i have. i dont know anyone else that had troulbes like i did but i went through a lot to set it up right so it woudl actually start lol. starts strong now and the high idle goes out a lot quicker. i like the way it fires up now