Why my car commanding too rich fuel in the startup

[wesam]

I noticed when the weather is cold and the car is parked for the night when i start it its command too rich in the first 10 seconds and it seems that it will die
i know there is table A0008 for Open loop ECT commanded fuel multiplier but i don't want to change it because its perfect now i just want to know which table in COS3 responsible for commanded fuel at start-up
also it start climbing from this rich area to my commanded 14.7 area and take a long time nearly 7 minutes so how could i make it reach the 14.7 faster than that
attached log for the problem

[swingtan]

Tune file would help, however....



{B3604}
{B3632}
{B3662}
{B3627}
{B3628}
{B3650}
{B3663}
{B3664}
{B3665}


That should keep you busy for a bit....

Simon.

[wesam]

Thanks Simon i took a glance on those table before i post the thread but i don't know where to start
i think i should start at B3604 but I'm afraid to damage some thing
here is my tune file

[swingtan]

There should be no danger of damage, just an engine that wont want to run....

Try this as an example.

[eficalibrator]

On a completely stock engine, extra fuel is added in cold environments on purpose to make up for the reduced amount of evaporation. At a glance, this looks like you're asking the engine to run as rich as 11.0:1 or worse but that's not what the cylinders see. If only some percentage of the fuel being injected is evaporating, then combustion is only happening at the ratio that correlates with the evaporated fraction of fuel delivered. The rest just passes through in liquid form as "lost fuel".

So how does this affect modified cars? Well, if you correctly recalibrate all the air and fuel flow models (complete injector data, VE surface, VVE coefficients, MAF transfer) at normal warmed up temperatures, then there shouldn't be too much work left to do here. The cold start tables are all adders or multipliers to the warmed up fuel delivery. If you get the actual airmass estimates right on the money for normal operation, chances are that the warmup fueling needs the same RELATIVE adjustment. A lot of people run into problems when they shortcut the base mapping process and bake in errors to the air model. These baked in errors get multiplied during transients and cold start, giving some of the symptoms described above. Before you spend too much time reinventing the wheel with cold start adders, I'd double-check the accuracy of your MAF and VE based fueling in open loop.

[swingtan]

Correct, but the initial evaporation issues are only present for the first few seconds of the cold engine start. A large fraction of the injected fuel will reside in the intake in the form of wall wetting, eventually all that fuel must find its way into the cylinders and provide a richer mixture. You can see this in the log file provided in post #1 where after about 23 seconds, the WB reading matches the commanded fueling. When the engine is first fired, the "very" rich mixtures for cranking are the ones that suffer from the fuel not vaporising. So you can command something like 3:1 AFR when cranking and still have the engine fire. As soon as it does though, the mixtures need to lean out a lot to provide a "rich cold idle", somewhere around normal PE values usually works OK. This is because once running, the MAP, air flow and valve temps all produce much better conditions for fuel vaporisation.

So getting back to the original post....

The first 10 seconds is most influenced with both commanded cranking fuel and post start enrichment.

Following the first 10 seconds, fueling is most influenced by post start enrichment only.

Your engine dying just after a cold start is possible due to idle flare control as well. Take a look at {B5943} and Minimum final timing (B5915}. these may help as well.


Simon

[wesam]

Simon
i noticed the same issue in cold weather also when the ECT is in normal operating temperature
i mean when i drive the car fro 30 min and park it for 15 min then start it again the ECT will be some thing like 80*c but the commanded fuel will start from a rich point like 11:1 and start climbing but faster than a cold start
i hope this will help

[redhardsupra]

A lot of people run into problems when they shortcut the base mapping process and bake in errors to the air model.

This should be framed on every wall of every gear-head's garage, as it is the leading cause behind just about every half-baked tuning procedure.

[swingtan]

Yes, that is true, but when the WB AFR is tracking very close to the commanded AFR, we know that the base mapping must be pretty good. This is what we see in the OP's original post. Personally I've always felt that the stock GM tunes are a bit generous with the after start enrichment. Most street cars should idle fine on an AFR in the 12's just after start and be fine with the mixtures leaning out quite quickly. Personally my 6lt motor will command stoich within a minute of starting if it's 20'C outside. Te basics still must be right though, if the car doesn't idle well normally, it's going to struggle when cold.

Simon.

[wesam]

Simon i got the problem it was A0008
Its strange because i thought its affect the VE table because its a multiplier but when i tried to make it 1
its now commanding 14.7 from the beginning
so actually A0008 is affecting the commanded fuel not the VE table
Case is closed
thanks every body

[swingtan]

That's interesting....

A0008 is pretty much the same as B3632.

I can only assume that in some OS's, B3632 does not exist, requiring a separate table, the only difference being that B3632 is an "adder" table and A0008 is a multiplier. As both of these tables are populated in your tune, it would add lots of fuel.

Simon.

[joecar]

A0008 is a multiplier to B3647, see description:


When using {B3647} "Commanded Fuel vs RPM (Normal)" to define the commanded fuel, this table is used as multiplier based on engine coolant temperature.
A number of 1.00 will add no more fuel based on the engine coolant temp, any number higher than that will add fuel.


B3647 is the OL commanded fuel table in the COS's.

[swingtan]

Yes, I wasn't very clear was I.....

I should have said that those tables can achieve similar if not the same result, adding additional fuel after the initial start. Both appear to act on B3647, A0008 as a multiplier and B3632 as an adder.

simon

[Sid447]

Wesam,

Your log doesn't show any air pids; If it did I'd guess at saying your engine isn't getting enough air.
Your tune looks like it needs some work on the air side.

You also still have some A4 parameters in the tune (desired airflow and TF tables to name just two, there are quite a few others).

It might be better to sort this out before any adjustments to initial start fueling.