Tips for better E85 cold start on 4G63T

[JB9]

Hi! I'm in Sweden and need cold start to work somewhat OK down to at least 0degC.

I'm running my Evo IV on pump E85, so probably around 75% EC. Bosch 870cc injectors.

Fully warmed up it idles somewhat stable now, around Lambda 1.0, 6deg BTDC, and 850rpm.

Today I tried a cold start at 14degC ambient temp. Took a few seconds of cranking, but it started up quite ok. But to get it to this point, I have had to set crank enrichment to the maximum of 600%, so at a colder ambient temp it will still struggle a lot, since I can't increase it more. Pre-crank prime at this ambient temp is set to ~28-29.

Could someone point me in the right direction here? Surely I shouldn't have to max out crank enrichment for it to start decent? Am I going about this all wrong?

[koracing]

^{can you post a copy of your tune and a datalog?}

why is the font so small in the first part of this post?

[Adamw]

To give a bit of theory; for combustion you need fuel vapor, the burning rate of liquid fuel is too slow to create combustion on its own.  Fuels like petrol/gasoline have a high vapor pressure which means they readily create lots of vapor even at low temps with very little encouragement.  You can have big ass injectors with poor atomisation and a poor tune and it will still light up easy.  Ethanol on the other hand has a very low vapor pressure and at low temps it barely generates any vapor at all.  When only a very small percentage of that liquid fuel is vaporising then to get enough vapor for combustion the common strategy is just dump lots of fuel in.  However just "dumping lots of fuel in" only goes so far - you get to a point where to get enough vapour you will end up with too much liquid fuel in the port and chamber and igniting that becomes very difficult and you go backwards.  

OEM cars designed to run on flex fuel will use strategies to encourage more vapor such as a small injector with a fine atomisation often coupled with high fuel pressure and strategies such as timing the injection event while port velocity is highest or timing the injection event when maximum port vacuum occurs.  Even with those tricks however high ethanol content cold start is still very troublesome - this is why in most countries with even moderate climates the fuel suppliers drop ethanol content in winter.  The extra little bit of petrol is needed to create enough vapor.   In countries like Brazil where they run on E100 they use special heated injectors with fine atomisation to generate vapor to aid cold start. 

So, in a performance situation where you often have large injectors with poor atomisation (or even just less than perfect) then the odds are against you.  If you are already at 600% enrichment then I dont think just dumping in more fuel will help.  You need to look at other ways to increase fuel vapor in the combustion chamber.

 

 

[koracing]

Keep in mind the cranking enrichment is a percentage based on the base fuel table values, and you also have start prime, and first crank enrichment options to inject additional fuel.  I don't see any reason 870cc injectors should require 600% enrichment to fire up decently cold.  I've had 2200cc injectors fire up on 75-80% ethanol at 40°F ~ 4°C just last week without issue.  Cranking enrichment was about 250% at that temp just FYI.  Dialing in warm running and starting first may be a better way to get where you need to be as you can spend a lot more time warm to perfect starting.

[JB9]

Thanks guys! I'm quite familiar with the theory behind it all, its just that on my Saabs (the non-biopower ones) I run the worthless Siemens Deka IV injectors (they have even worse atomisation than these Bosch ones AFAIK) and they start up quite fine in cold without crazy amounts of fuel on startup, so I'm a bit baffled how this 4G63 can be so angry about this. Granted, those Saab engines (and the OEM ECUs) may of course have other characteristics making it easier for them.

Anyhow, I'm thinking maybe I should just zero out both the prime and crank enrich tables and start over? I took over after previous owner of the car had a "protuner" tune the car so I just continued where they left off.

Warm start and warm idle works fine. Maybe I should look into the idle steps on cold start as well? See if it maybe simply isnt getting enough air?

[KennyJ]

as a little question here : would it be better in this kind of situation do have a big or small opening of the idle valve ? 

[koracing]

To figure out if you need more air or fuel when cold starting: crack throttle slightly (Maybe 2-10%) while cranking cold and see if it improves, or makes it worse, or no change.  Setting up a full throttle flood clear can be useful here to clear the cylinders if you think it's over-fueling.  If none of that makes any difference, try spraying a spritz or two of starter fluid or carb cleaner into the throttle body and see if it wants to light off (artificially adding more fuel vapor).  Something here should lead you in the proper direction of if the motor is wanting more fuel or more air.