I made a video of a cold start on 1/19. It was near 0*F over night and probably around 5 or 6* at the time of cranking. Here is the video:

http://kmoore.phzero.net:8081/my%20p...cold_start.avi

It's 800k so it should be managable for everyone.

Basically what it does is, after cranking for a while (which I have learned to accept with TBI), fires and revs to like 500rpm or 600rpm, then quickly falls a bit, then continues to startup flare (slowly). I am almost positive it's getting too much fuel at the time the engine bogs. I think this because I recently adjusted my throttle stop screw so that IAC counts are around 5 steps at hot idle (much more open than it was before). The opening of the TB has made startup better, since there's more air to go with the fuel. However, this behavior is still present.

What I want to know is, what tables in Tunercat do I mess with to fix it? In the past, I spent a lot of time trying to fix this problem, but recently reset everything back to stock. What you see in the video is bone stock startup tables and stock BPC. Consider the engine "stock" for startup purposes.

I have these tables to play with:

Startup AFR Decay Multiplier vs Coolant temp


Crank AFR Multiplier vs Vacuum


Air Fuel Ratio at Startup vs Coolant Temp (Choke)


Crank Air Fuel Ratio vs Coolant Temp


These are all stock. Any idea what I should tweak here? I think the initial cranking AFR is fine. It's just when the engine fires that it is shot with too much fuel (choke?). And when it settles into an idle, it's a bit rough. Exhaust confirms rich there, too. Perhaps both can be fixed with just one table?

Warm start is acceptable, so I don't want to change anything that isn't referenced to coolant temp.

This is for my Caprice, L05, $62 mask.

 

The choke table is subtracted from the open loop AFR table(s). So if your open loop AFR at that engine temp and MAP were 14 and the choke AFR was 2 the commanded AFR would be 12.
The startup decay is how fast the choke AFR gets decayed away. Higher the number the slower it takes to zero out resulting in just the open loop AFR.
That crank multiplier vs vac is an odd table but cool! If that's a true multiplier then there is some math being done that is unknown to me. Because if the crank AFR table was 9 and the multiplier were .3 that's an AFR of 3. Cranking with that much fuel would surely flood an engine. Then again that value might be subtracted from the open loop AFR, who knows. Just play with one table at a time. I know this is going to take a couple days to figure out but it shouldn't be too difficult.
I'd start with the last 2 tables in your post since your warm and hot starts are all okay.

 

I thought I had it figured out once! I would lean out the crank AFR then decrease the decay multiplier. According to what you wrote, I was way off. Tunercat also has some things to say in the $42 help file. Please allow me to paste, to further confuse the matter:

Air Fuel Ratio at Startup Vs. Coolant Temp. (Choke)

This cold engine AFR vs. coolant temperature table is used to control engine AFR after the ECM has gone into “closed loop” and prior to reaching normal (or near normal) operating temperatures.


Choke Air Fuel Ratio Multiplier Vs. Coolant Temp.

This table contains a multiplier to the crank air fuel ratio table that is applied as the crank engine speed increases up to the value of RPM assumed to be a running engine. The intent is to reduce the “choke” fuel when the engine is "marginally" running.


Crank Air Fuel Ratio Vs. Coolant Temp.

This table simulates a “choke” condition for cold engine start up. The air fuel ratios shown are used until the engine is running in reasonably stable condition.


As you can see, somebody is wrong here. TC hasn't written a $62 help file. Maybe I should bug hum for the nth time to offer some insight in what my tables do. You know, it's possible there are other tables that he hasn't dug out yet (I've e-mailed him for about 13 $62 updates over the years...). I think the original $62 was missing at least one of the 4 startup tables I posted.

 

That's all wrong, I'm right . I'm not just joking. His descriptions for one mask aren't (and usually aren't) universally true for another. There's a reason why GM used so many different masks.
If what you posted is in the help file then ignore that for the $42 mask because there are huge mistakes in his descriptions. I'd comment on them but just ignore that file and try what I told you. Then get back to me. Also, try going BOTH ways, not just leaning it out. You'd be suprised how often you think you're rich when you're lean and vice versa. Also, have you touched the timing tables? You could be running too much timing (base and computer added) although startup spark SHOULD be limited to the esc until the ecm detects enough RPM to accept control.

 

I think the startup flare bogs precisely when the ECM takes over control of the engine. Like I said before, I think it's rich because it flares better after I opened the TBs some.

Hopefully I'll have a chance to experiment some this weekend.

I just ordered a 24-pin ZIF from moates. Any tips for soldering it in my '6965? I have no calpak in this ECM, just the EPROM carrier. A friend suggested I wick the solder out, to get the factory holder socket out of there.

 

I halved my choke fueling in cold temps (which dropped the choke AFR subtracter from about 3.0 to 1.5), and this morning, it seemed to start the same from a 14°F coolant temp. I was expecting at least a difference.

It does start acceptably in 40°F coolant temps, which is good.

Next thing I will try is just zeroing out the choke. This may be the wrong table to use for the transient issue I'm chasing. I think the problem occurs when the ECM takes over the startup idle flare.

Also, on the startup AFR decay multiplier - that multiplies the choke AFR by that number every so often until choke is decayed to nothing? Is that correct? So lower numbers phase out the choke faster? What about "1?" Maybe TC won't accept a value of "1."

 

You don't necessarily want to run too lean on a cold start. If you do, remove some of the choke SA as well. The idea behind the running rich and lots of SA was to get everything up to temp faster (burn more fuel, more energy released as heat into the coolant and exhaust).
I think you're doing everthing correctly.

 

I think I made it too lean. It did make a change, but not in startup. After it starts and the idle settles, the engine feels different. It's no longer lightly misfiring, but it's running rougher all around. Actually, it feels a LOT like my 95 Z28 at idle. No misfiring, but just a general rough feeling. I think it's too lean now. Drivability is not crisp. It feels lean.

So I will add back in some choke fuel, and probably work on another table to combat the startup issue. I think I'll mess with crank AFR.

I scaled the cold crank AFR areas by 1.25, leaning them out. We'll see what happens.